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  • Disentangling abiotic and biotic controls of aerobic methane oxidation during re-colonization
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-23
    Thomas Kaupper; Janita Luehrs; Hyo Jung Lee; Yongliang Mo; Zhongjun Jia; Marcus A. Horn; Adrian Ho

    Aerobic methane oxidation is driven by both abiotic and biotic factors which are often confounded in the soil environment. Using a laboratory-scale reciprocal inoculation experiment with two native soils (paddy and upland agricultural soils) and the gamma-irradiated fraction of these soils, we aim to disentangle and determine the relative contribution of abiotic (i.e., soil edaphic properties) and biotic (i.e., initial methanotrophic community composition) controls of methane oxidation during re-colonization. Methane uptake was appreciably higher in incubations containing gamma-irradiated paddy than upland soil after inoculation with both native soils despite of different initial methanotrophic community composition, suggesting an overriding effect of the soil edaphic properties in positively regulating methane oxidation. Community composition was similar in incubations with the same starting inoculum as determined by quantitative and qualitative pmoA gene analyses. Thus, results suggested that the initial community composition affects the trajectory of community succession to an extent, but not at the expense of the methanotrophic activity under high methane availability; edaphic properties override initial community composition in regulating methane oxidation.

    更新日期:2020-01-23
  • Response of bacterial communities and plant-mediated soil processes to nitrogen deposition and precipitation in a desert steppe
    Plant Soil (IF 3.259) Pub Date : 2020-01-22
    Zhen Wang, Risu Na, Liz Koziol, Michael P. Schellenberg, Xiliang Li, Na Ta, Ke Jin, Hai Wang

    Abstract Background and aims Changes in nitrogen (N) and precipitation levels can substantially alter soil properties and plant growth, thereby altering soil microbial diversity and functionality. Method We used manipulated precipitation treatments (50% reduction, control, and plus 50%) and tested two N fertilization levels (control and plus 35 kg N ha−1 yr−1) from a 4-year field experiment to evaluate the effects on soil bacterial diversity, community composition, and N-cycle gene abundance. Results N additions significantly increased ammonia-oxidizing bacterial abundance (via AOB-amoA) but decreased denitrification genes (i.e., nirS and nosZ). Decreased precipitation significantly decreased the abundance of N-cycle genes (AOB-amoA, nirS, and nosZ), while increased precipitation conversely increased the abundance of these same genes. Decreased precipitation led to differences in the microbial community composition that favored drought resistance, indicating that plant-associated microbiomes may be able to modulate plant growth fitness in the context of extreme environmental conditions. N additions substantially altered soil bacterial communities, increasing the relative abundance of certain bacteria and of nitrification-related genes in a manner that depended on precipitation fluctuations. Conclusions Differences in the bacterial community composition and N-cycle genes determined the functional response of a grassland ecosystem to decreased precipitation conditions, and therefore could affect the influence of N deposition on plant growth as well as the physical and chemical properties of the soil.

    更新日期:2020-01-23
  • Micro-food web interactions involving bacteria, nematodes, and mycorrhiza enhance tree P nutrition in a high P-sorbing soil amended with phytate
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-22
    Mahafaka Patricia Ranoarisoa; Jean Trap; Anne-Laure Pablo; Damien Dezette; Claude Plassard

    Phytate is considered a poorly available plant P source but proved to be useful for particular soil bacteria strains. In soil-free conditions, it has been shown that bacteria locked up the mineralized phosphorus from phytate whereas bacterial grazers like nematodes were able to deliver P to plants. Here, we aimed to determine if the interactions between phytate-mineralizing bacteria, bacterial grazer nematodes, and mycorrhizal fungi could increase plant P acquisition from phytate in high P-adsorbing soils. Pinus pinaster was grown in a Cambisol supplemented with phytate. Plants, whether associated or not associated with the ectomycorrhizal fungus Hebeloma cylindrosporum, were either inoculated or not inoculated with the phytase-releasing bacteria Bacillus subtilis and the bacterial-feeding nematode Rhabditis sp. After 100 days, the dual inoculation of bacteria and nematodes significantly increased net plant P accumulation. We observed that, on average, mycorrhizal plants accumulated more P in their shoots than non-mycorrhizal plants. However, the highest plant P acquisition efficiency was found when the three soil organisms were present in the P. pinaster rhizosphere. We conclude that, in a highly inorganic P-fixing soil, plant P acquisition from phytate strongly depends on the grazing of phytate-mineralizing bacteria. Our results confirm the importance of the soil microbial loop to improve plant P nutrition from phytate, which should be considered a route to improve the utilization of this source of poorly available P by plants.

    更新日期:2020-01-23
  • Nitrite accumulation and nitrogen gas production increase with decreasing temperature in urea-amended soils: Experiments and modeling
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-22
    Rodney T. Venterea; Jeffrey A. Coulter; Timothy J. Clough

    Nitrite (NO2−) accumulation and associated production of nitric oxide (NO) and nitrous oxide (N2O) gases in soils amended with nitrogen (N) fertilizers are well documented, but there remains a poor understanding of their regulation and variation among soil types. We examined responses to urea inputs in two soils at five temperatures from 5 to 30 °C and developed a process-driven model to describe the dynamics. A microcosm system was used to measure ammonia gas (NH3), ammonium (NH4+), NO2−, nitrate (NO3−), NO, N2O and pH over 12 weeks. Unexpectedly, NO2−, NO and N2O production tended to increase as soil temperature declined in both soils. The maximum NO2− concentration, or compensation point (CP), differed by soil type but the time required to reach CP decreased exponentially with increasing temperature in both soils. A two-step nitrification model (’2SN’) accounted for interactions of ammonia-oxidation (AmO), nitrite oxidation (NiO), urea hydrolysis, NH4+ sorption, N gas production and pH dynamics. Both steps of nitrification (AmO and NiO) were modeled using NH3 inhibition kinetics. The model adequately simulated the observed dynamics and temperature responses and showed that increased uncoupling of AmO and NiO at colder temperatures resulted from their differential temperature responses. The dynamics observed here may be important following high-rate and banded N fertilizer applications and in ruminant urine patches. The results may help explain elevated N2O emissions observed under cold temperatures. The 2SN model can account for interactions among multiple processes and may be useful for studying the effects of management practices and climate factors, including climate change scenarios, on soil N cycling.

    更新日期:2020-01-22
  • Addition of fructose to the maize hyphosphere increases phosphatase activity by changing bacterial community structure
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-22
    Lin Zhang; Yi Peng; Jiachao Zhou; Timothy S. George; Gu Feng

    Organic forms of phosphorus (P) tend to accumulate in soils with long-term fertilization, however they are generally not easily available to crops. Many crop plants are obligately arbuscular mycorrhizal (AM) and AM fungi are known for not being able to produce phosphatases, the enzyme involved in the mineralization of organic P. AM fungi are able to recruit bacteria in the hyphosphere which can produce phosphatases and access organic P. It is thought that fructose produced by AM fungi acts as a signal to select these bacteria. We designed a system to test whether fructose could stimulate phosphatase activity in the maize hyphosphere. The concentration of fructose produced by AM fungi and the large concentration of fructose equivalent to the entire concentration of hyphal exudate carbon, were added. Small concentrations of fructose did not stimulate phosphatase activity in soil, cause shifts in bacterial community structure or select phosphatase producing species. However, at large concentrations of fructose, phosphatase activity was increased and this was associated with a larger bacterial population and a shift in bacterial community structure towards species which specialized in using fructose and glucose for energy metabolism, such as Saccharibacteria. Nevertheless, there was no specific shift towards species which harbored alkaline phosphatase genes and it is suggested that the change in phosphatase activity was due to subtle shifts in the properties of the phosphatases being produced. These results suggest that fructose was unable to act as a signal to select phosphatase producing bacteria in soil, but could act as an energy source to stimulate phosphatase activity by shifting soil bacterial community structure.

    更新日期:2020-01-22
  • Both vacant niches and competition-trait hierarchy are useful for explaining the invasion of Caragana microphylla into the semi-arid grassland
    Plant Soil (IF 3.259) Pub Date : 2020-01-21
    Ke Dong, Yujuan Xu, Guang Hao, Nan Yang, Nianxi Zhao, Yubao Gao

    Abstract Aims Trait-based coexistence theories are useful to explain community processes. The aim was to distinguish which theory played a more important role in explaining the invasion mechanism of Caragana microphylla into communities in the Eurasian semi-arid grassland region. Method We conducted a water condition (WC) × neighbouring plant diversity (NSD) experiment, measured functional dispersion (FDis) and biomass of neighbours, absolute and hierarchical distances between neighbours and C. microphylla for plant height, specific leaf area and leaf dry matter content (LDMC), and explored the relative effect of each predictor on neighbour-effect intensity index (NIntA) on C. microphylla. Results Significant effect of NSD was direct or mediated by cascading effects between FDis and biomass of neighbours, significant effect of WC was direct or mediated by LDMC hierarchical distance, shoot biomass of neighbours mediated indirect effects of both NSD and WC on the NIntA on C. microphylla. None of the trait absolute distances was employed to explain the variability of the NIntA on C. microphylla. Conclusions The reduction of NSD or water could decrease the inhibitory effects of neighbours on C. microphylla by increasing vacant niches or increasing the LDMC hierarchical distance between neighbours and C. microphylla, respectively, suggesting that vacant niches and competition-trait hierarchy played more important roles than competition-trait similarity in explaining shrub invasion processes in the Eurasian semi-arid grassland region.

    更新日期:2020-01-22
  • Do diversity of plants, soil fungi and bacteria influence aggregate stability on ultramafic Ferralsols? A metagenomic approach in a tropical hotspot of biodiversity
    Plant Soil (IF 3.259) Pub Date : 2020-01-21
    Julien Demenois, Luis Merino-Martín, Nicolas Fernandez Nuñez, Alexia Stokes, Fabian Carriconde

    Abstract Aims Understanding how soil aggregate stability (MWD) is influenced by microbial diversity and abundance can be crucial for ecological restoration in severely disturbed areas. We investigated the relationships between plant and soil microbial diversity and MWD of an ultramafic Ferralsol along a vegetational succession gradient in New Caledonia, where wildfires and extensive nickel mining have degraded the landscape. Methods Five plant communities were studied. For each one, MWD, soil physicochemical parameters (e.g. soil organic carbon (SOC)), plant root traits and fungal abundance were measured. The diversity and structure of plant and microbial communities were respectively assessed via botanical inventories and a metagenomic approach. A generalized linear model (GLM) was used to assess the influence of diversity indexes on MWD. Constrained ordinations (CCA) were performed to assess the influence of communities’ structures on MWD. Results GLM highlighted the linkage between SOC and MWD but did not identify any significant influence of diversity indexes on MWD. CCA revealed a significant influence of communities’ structures, especially the abundance of saprotrophic fungi, on MWD. Conclusions We showed that the structure, but not species richness and diversity of plants, soil fungi and bacteria influence aggregate stability on Ferralsols.

    更新日期:2020-01-22
  • Metamodelling a 3D architectural root-system model to provide a simple model based on key processes and species functional groups
    Plant Soil (IF 3.259) Pub Date : 2020-01-21
    Loïc Pagès, Olivia Pointurier, Delphine Moreau, Anne-Sophie Voisin, Nathalie Colbach

    Abstract Aims The architecture of root systems determines where and how much resources plants can extract from the soil, how they compete for soil resources, and how they interact with soil organisms. We aimed to develop a 3D root-system model called RSCone for future inclusion into multispecies individual-based canopy models suitable to design integrated weed management or intercropping strategies. Methods We (1) proposed a conceptual root-system model consisting of empirical equations predicting root-system envelope, root length and biomass distribution from environmental conditions, species and plant stage, (2) calibrated the model from simulations with an existing architectural root-system model (ArchiSimple) to benefit from its knowledge on root functioning and the many parameterized crop and weed species, (3) identified the root-system architectural processes driving the key root state variables and (4) established species functional groups with Principal Component Analyses and clustering. Results RSCone consists of 17 equations and 14 parameters; it was calibrated for 22 weeds and 22 crop species and varieties. Six species functional groups were established, depending on their family (Poaceae, Fabaceae, other), root-extension rates, specific root length (SRL) and the time to reach maximum SRL. Conclusion RSCone is ready to be included into multispecies (crop and/or weed) dynamics models.

    更新日期:2020-01-22
  • High ecosystem multifunctionality under moderate grazing is associated with high plant but low bacterial diversity in a semi-arid steppe grassland
    Plant Soil (IF 3.259) Pub Date : 2020-01-21
    Xinyu Wang, Frank Yonghong Li, Yanan Wang, Xinmin Liu, Jianwei Cheng, Junzhen Zhang, Taogetao Baoyin, Richard D. Bardgett

    Abstract Aims Current studies on the relationship between biodiversity and ecosystem functioning have mostly focused on plant communities. Less is known about the individual and combined effects of biodiversity components above-and-below-ground on ecosystem multifunctionality. The aim of this study was to explore how different management regimes influence multifunctionality via modification of both plant and soil microbial (bacterial and fungal) diversity. Methods We used a 6-year experiment in Inner Mongolian grassland to compare multifunctionality and separate functions related to the C, N, P cycles and plant productivity under four management regimes and examine relationships between these functions and different components of biodiversity, both above- and belowground. Results Ecosystem multifunctionality and the rates of nutrient cycling and plant productivity, were greatest under moderate grazing intensity, and lowest under no grazing. Further, across all management regimes, multifunctionality was positively related to plant diversity, and plant and soil microbial diversity combined explained a much greater (62.5%) proportion of variance in multifunctionality than that did either component alone. Different components of biodiversity showed contrasting relationships with individual functions: plant diversity was positively related to C and N cycling, whereas bacterial diversity was negatively related to P cycling and plant productivity. Conclusions Moderate grazing has better outcomes for biodiversity conservation and ecosystem multifunctionality than mowing and cessation of grazing. Sustainable grazing management is a viable strategy to conserve both above- and belowground biodiversity and enhance the delivery of multiple ecosystem functions.

    更新日期:2020-01-22
  • Contribution of plant litter and soil variables to organic carbon pools following tropical forest development after slash‐and‐burn agriculture
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-21
    Shaojun Wang; Minkun Chen; Run Cao; Qianbin Cao; Qianqian Zuo; Ping Wang; Bo Yang; Shuang Zhao

    Tropical forest development after slash‐and‐burn agriculture crucially affects soil carbon accumulation. However, it remains unclear how the dynamics of soil organic carbon (SOC) pools are regulated following tropical forest restoration. Our study aims to quantify the contribution of litter and soil variables to alterations in carbon pools during tropical forest restoration on slash‐and‐burn agricultural land in Xishuangbanna, Yunnan, China. This study observed a significant increase in soil carbon pools along forest restoration. The extent of the increase in labile fractions (1.9–2.5‐times) was higher than that of SOC (1.5‐times) during the restoration from early to later stages. The proportion of microbial carbon to total carbon increased from 3.0 to 7.7% during forest restoration, while those of dissolved (5.3–3.1%) and readily oxidizable (42.9–29.6%) fractions decreased. Clay content determined the accumulation dynamics of SOC (10.5%) and labile fractions (6.0–13.5%) in the later stage, while free Fe oxides (10.4–15.4%) contributed to these pools mainly in the early stage. Microbial carbon explained 22.4–26.7% and 20.6–28.3% of the variation in SOC stocks and labile fractions, respectively, whereas litter carbon accounted for 9.5–15.3% of the change in microbial carbon stock. The contribution (8.2–17.1%) of litter‐soil nutrient interactions to carbon pools increased during forest restoration. Our data suggest that carbon dynamics are mainly determined by variations in the clay content, free Fe oxides, and litter and microbial carbon, possibly through nutrient‐level interactions between the litter and soil during tropical forest restoration.

    更新日期:2020-01-22
  • Five‐year soil moisture response of typical cultivated grasslands in a semiarid area: Implications for vegetation restoration
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-21
    Zhi‐Qiang Dang; Ze Huang; Fu‐Ping Tian; Yu Liu; Manuel López‐Vicente; Gao‐Lin Wu

    Soil water deficit is one of the important abiotic stresses affecting vegetation restoration. The magnitude and spatiotemporal dynamics of soil water content (SWC) provide basic guidance for optimal vegetation restoration. In a semiarid Chinese area, the changes in the soil water storage (SWS) of five cultivated grasslands and one wasteland were observed, to evaluate the water consumption at different soil depths (0–100 cm), from 2008 to 2012. The plants of the three leguminous species consumed more water in deep soil layers (80–100 cm) and produced more aboveground biomass than the plants of the two gramineous species. The gramineous plants mainly consumed shallow soil water (0 ≤ 30 cm). The soil water deficit in the whole soil profile of Medicago sativa grassland (43–48%) was significantly higher than the deficit of the gramineous grasslands (p < .05). After 5 years of planting, the SWC of Agropyron cristatum grassland (21%) was the highest in the 20‐ to 80‐cm soil layer. The variation of SWS in M. sativa grassland did not significantly differ during this period, although its mean value was 28% lower than the value in A. cristatum grassland (181 mm). At the end of the experiment, leguminous grasslands caused a serious soil water shortage deficit in the 80‐ to 100‐cm soil layers. These results underscore that vegetation type determines the vertical distribution of soil water deficit, particularly in deep layers. To promote long‐term sustainability of water resources, planting A. cristatum may be a good choice for early grassland restoration in arid areas.

    更新日期:2020-01-22
  • Environmentally Sensitive Areas to Land Degradation and Desertification (LDD) at the Global Level: Updating the MEDALUS‐ESA Framework for Worldwide LDD Assessment
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-20
    Agostino Ferrara; Constantinos Kosmas; Luca Salvati; Antonietta Padula; Giuseppe Mancino; Angelo Nolè

    The Environmentally Sensitive Area (ESA) methodology (originally proposed in the framework of MEDALUS ‐ Mediterranean Desertification and Land Use ‐ a series of international cooperation research projects funded by the EU) is used worldwide to identify ‘sensitive areas' that are potentially threatened by land degradation and desertification. The distinctive outcome of this approach is a multidimensional index (the ESA index) composed of partial indicators of climate, soil, vegetation, and management quality that are derived from the elaboration of 15 elementary variables. In this study, we propose (i) a major update of the ESA methodology, as presented in the MEDALUS project, for global land degradation/desertification (LDD) assessment, (ii) a global map of ESAs to LDD and (iii) a global environmentally critical factors (ECF) map. The results of the updated ESA framework confirm the efficiency and applicability of the ESA methodology in different worldwide areas, allowing for the harmonization of regional/country level studies and applications, and the more efficient use of global level datasets. In this study, we provide examples for analysis of LDD patterns and processes at a global level, as well as for identification of the main risk factors over time and space. Global‐ESA and Global‐ECF maps also support regional‐scale knowledge on LDD processes and sustainable land management practices for LDD mitigation. High‐resolution illustrative maps and other information are available on a dedicated website (http://web.unibas.it/global‐esa/).

    更新日期:2020-01-22
  • Land cover mapping based on time‐series MODIS‐NDVI using a dynamic time warping approach: A casestudy of the agricultural pastoral ecotone of northern China
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-20
    Baocheng Wei; Yaowen Xie; Xiaoyun Wang; Jizong Jiao; Sijia He; Qiang Bie; Xu Jia; Xiaoyu Xue; Hanming Duan

    To curb land degradation, a series of ecological restoration projects have been carried out since 1999, leading to dramatic land cover change (LCC) in the agricultural pastoral ecotone of northern China (APENC). To date, there is still lack of timely and accurate land cover (LC) information for management and assessment actions. This paper presents a LC mapping scheme to map annual LC information based on dynamic time warping (DTW) approach and time‐series MODIS‐NDVI product for the APENC. The DTW approach was optimized firstly based on the change of vegetation phenology phase. Next, typical reference time‐series curves set of different LC types were established and pixel‐wise similarity was examined to identify the LC type. Before that, the reconstruction of time‐series MODIS‐NDVI was performed using harmonic analysis of time‐series and reconstruction accuracy was evaluated quantitatively at a regional scale. Results showed that the gap error was relatively large for the high vegetation cover areas while it might be ignored for the moderate and low vegetation cover areas. The overall accuracy of LC mapping in year 2010 (LC‐2010) was 77.89% and kappa coefficient reached 0.71, which suggested that LC mapping scheme could extract LC information with high accuracy. The producer's accuracy ranged between 69.83% (grasslands) and 100% (water body), while the user's accuracy changed from 58% (built‐up) to 86% (forest). The overall spatial agreement between LC‐2010 and GlobaLand30‐2010 was about 64.44%. The total area of forests, croplands, water body and built‐up exhibited an increasing trend while the contrary trend were found for the grasslands and bare land during the 2001–2017. These LC maps are valuable for research the land degradation investigation and monitoring, benefit evaluation of ecological restoration projects and effect of LCC on surface hydrothermal process in APENC.

    更新日期:2020-01-21
  • Live barriers and associated organic amendments mitigate land degradation and improve crop productivity in hillside agricultural systems of the Ecuadorian Andes
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-18
    Mark Caulfield; Jeroen C. J. Groot; Steven J. Fonte; Stephen Sherwood; Pedro Oyarzun; Ross Mary Borja; Sam Dumble; Pablo Tittonell

    Land degradation caused by erosion and nutrient depletion in the Andes poses serious existential threats to small‐scale farming. While the potential of hedgerows to decrease water erosion is well recognised, their potential dual‐use as a source of organic amendments to supplement farmer inputs is much less studied. The objective of this investigation was therefore to explore locally‐developed options for hedgerows that address these twin challenges. Experimental plots were installed to assess water erosion control by hedgerows and the effect of organic amendments harvested from the hedgerows on soil productivity, soil moisture and soil fertility over the course of two years and three crop cycles (two of barley, one of rye). The experiment was conducted in two sites within the community at distinct elevations and associated biophysical contexts. At each site four treatments were established, comparing a control treatment vs. three types of hedgerows: 1) Andean alder, 2) canary grass strips, and 3) mixed canary grass and Andean alder. Results demonstrated that hedgerows and associated organic inputs comprised of canary grass, and mixed canary grass and Andean alder reduced water erosion by 50‐60% and increased biomass production by up to 1.1 Mg ha‐1 and grain yield by up to 0.5 Mg ha‐1. We conclude that while hedgerows are unlikely to produce sufficient quantities of organic resources to satisfy all nutrient input requirements, their potential to decrease erosion and supplement existing organic matter inputs indicates that they should be strongly considered as an option for improved agricultural management within this and similar resource constrained contexts.

    更新日期:2020-01-21
  • The forb, Ajania tenuifolia, uses soil nitrogen efficiently, allowing it to be dominant over sedges and Graminae in extremely degraded grasslands: implications for grassland restoration and development on the Tibetan plateau
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-17
    Rui Zhang; A. Allan Degen; Yanfu Bai; Tao Zhang; Ximing Wang; Xueyong Zhao; Zhanhuan Shang

    Plant growth is mainly N‐limited in the alpine grasslands because of slow mineralization of soil organic matter due to low air temperature. Different plant species dominate in soils of different N concentrations. For example, more forbs occur in severely degraded alpine meadows than do sedges and Gramineae. We hypothesized that a more efficient uptake of low soil N by forbs than by sedges and Gramineae was the mechanism that allowed forbs to dominate. The amount and rate of soil N uptake and N allocation were determined in seven dominant alpine plant species using 15N isotope tracer. The plants, which included 1 forb, Ajania tenuifolia, 3 sedges, Kobresia humilis, Carex scabrirostris and Carex enervis and 3 Gramineae, Elymus nutans, Festuca sinensis and Stipa purpurea, were maintained in pots with 4 different N concentrations (0, 50, 100, 150 kg ha−1). The forb had the highest efficiency of N utilization (N uptake rate, 60.4%) in low N soil concentration, the Gramineae had intermediate efficiencies (27.9%–47.9%) and the sedges had the lowest efficiencies (5.2%–34.9%) and, consequently, our hypothesis was supported. N utilization of the seven species decreased with an increase in soil N concentration, from 32.1% at N50 to 18.0% at N150, which indicated that soil N uptake by plants was affected by soil N concentration. The mechanism used by forbs to be the dominant species in severely degraded alpine meadows was a more efficient utilization of soil N than Gramineae and sedges in conditions of low soil N. We concluded that plant species have different efficiencies in soil N uptake and utilization which allow them to adapt and survive in habitats of different soil nutrition levels. These results implied that forbs should be reduced, and that Gramineae and sedges should be planted and N be added during the restoration and development of severely degraded grasslands on the Tibetan plateau when the soil N content is low.

    更新日期:2020-01-21
  • Global desertification vulnerability to climate change and human activities
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-17
    Jianping Huang; Guolong Zhang; Yanting Zhang; Xiaodan Guan; Yun Wei; Ruixia Guo

    Desertification is the impoverishment of arid, semi‐arid, and some sub‐humid ecosystems. The assessment of global scale desertification vulnerability to climate change and human activity is important to help decision‐makers formulate the best strategies for land rehabilitation and combat global desertification in sensitive areas. There is no a global desertification vulnerability map that considers both climate change and human activities. The main aim of this study was to construct a new index, the global desertification vulnerability index (GDVI), by combining climate change and human activity and climate change, provide another perspective on desertification vulnerability on a global scale and project its future evolution. Using the probability density function of the GDVI, we classified desertification vulnerability into four classes: very high, high, medium, and low. The results of the analysis indicated that areas around deserts and barren land have a higher risk of desertification. Areas with a moderate, high, and very high desertification risk accounted for 13%, 7%, and 9% of the global area, respectively. Among the representative concentration pathways (RCPs), RCP8.5 projected that the area of moderate to very high desertification risk will increase by 23% by the end of this century. The areas where desertification risks are predicted to increase over time are mainly in Africa, North America, and the northern areas of China and India.

    更新日期:2020-01-21
  • The effect of carbon availability on N2O emissions is moderated by soil phosphorus
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-20
    R.M. O’Neill; N.T. Girkin; D.J. Krol; D. Wall; F.P. Brennan; G.J. Lanigan; F. Renou-Wilson; C. Müller; K.G. Richards

    This research investigated the effect of long-term phosphorus (P) addition relative to carbon (C) availability on nitrous oxide (N2O) emissions from an ungrazed grassland soil via two incubation experiments. No significant effect of soil P on N2O was found under C-limited conditions, while under added-C, cumulative N2O was significantly higher from low-P (p<0.05) rather than high-P soils. CO2 was not significantly different between P-levels. This highlights the influence of soil P on N2O emissions under non C-limiting conditions. This is one of the first studies demonstrating available-C moderating the effect of P on N2O emissions from temperate grassland soils.

    更新日期:2020-01-21
  • Mineralization and nitrification: Archaea dominate ammonia-oxidising communities in grassland soils
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-20
    Dave R. Clark; Boyd A. McKew; Liang F. Dong; Garwai Leung; Alex J. Dumbrell; Andrew Stott; Helen Grant; David B. Nedwell; Mark Trimmer; Corinne Whitby

    In grasslands, N mineralization and nitrification are important processes and are controlled by several factors, including the in situ microbial community composition. Nitrification involves ammonia oxidising archaea (AOA) and bacteria (AOB) and although AOA and AOB co-exist in soils, they respond differently to environmental characteristics and there is evidence of AOA/AOB niche differentiation. Here, we investigated temporal variation in N mineralization and nitrification rates, together with bacterial, archaeal and ammonia-oxidiser communities in grassland soils, on different geologies: clay, Greensand and Chalk. Across geologies, N mineralization and nitrification rates were slower in the autumn than the rest of the year. Turnover times for soil ammonium pools were <24 h, whilst several days for nitrate. In clay soils, bacterial, archaeal, AOA, and AOB communities were clearly distinct from those in Chalk and Greensand soils. Spatially and temporally, AOA were more abundant than AOB. Notably, Nitrososphaera were predominant, comprising 37.4% of archaeal communities, with the vast majority of AOA found in Chalk and Greensand soils. AOA abundance positively correlated with nitrate concentration, whereas AOB abundance correlated with ammonium and nitrite concentrations, suggesting that these N compounds may be potential drivers for AOA/AOB niche differentiation in these grassland soils.

    更新日期:2020-01-21
  • The effect of organic acids on the behaviour and biodegradation of 14C-phenanthrene in contaminated soil
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-20
    Gabriela M. Vázquez-Cuevas; Alfonso J. Lag-Brotons; Jose J. Ortega-Calvo; Carly J. Stevens; Kirk T. Semple

    The interaction between root exudates and soil microbes has been hypothesised as the primary mechanism for the biodegradation of organic pollutants in the rhizosphere. However, the mechanisms governing this loss process are not completely understood. This study aimed to investigate the effect of two important compounds within root exudates (citric and malic acid) on 14C-phenanthrene desorption and bioaccessibility in soil. Overall results showed that the presence of both citric and malic acid (>100 mmol l−1) enhanced the desorption of 14C-phenanthrene; this appeared to be concentration dependant. Increases in extractability were not reflected in a higher bioaccessibility. Despite enhancing the desorption of 14C-phenanthrene in soil, there is no direct evidence indicating that citric or malic acid have the ability to promote the biodegradation of 14C-phenanthrene from soil. Results from this study provide a novel understanding of the role that substrates, typically found within the rhizosphere due to root exudation, play in the bioaccessibility and biodegradation of hydrocarbons in contaminated soil.

    更新日期:2020-01-21
  • The influence of biocrusts on the spatial pattern of soil bacterial communities: A case study at landscape and slope scales
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-20
    Yan-gui Su; Ying-Wu Chen; Francisco M. Padilla; Yuan-ming Zhang; Gang Huang

    Biocrusts are a functional unit in arid and semiarid areas, their development has significant recruitment and screening effects on soil microbial communities. Microbial composition of biocrusts exhibits significant geographical patterns, but the regulation of biocrust development on the geographical patterns in unclear. In this study, we examined bacterial communities from cyanobacterial-lichen and moss crust soils in five desert habitats in northern China, and evaluated the relative importance of environmental factors and biocrust development versus geographic distance to the distance–decay relationship. To explore the effects of the sampling scale on geographical patterns, we also examined soil bacterial communities along the slope of sand dunes. Across the five desert habitats, bacterial α-diversity, phylogenetic diversity, and the dominant bacterial phyla in cyanobacterial-lichen crusts did not increase consistently with precipitation increase, instead bacterial community composition was mainly impacted by soil nutrients (SOC, TP) and biocrust development (thickness, cover and Chl a). Bacterial β-diversity in both cyanobacterial-lichen and moss crusts showed strong distance-decay relationships across the landscape scale; bacterial community composition in cyanobacterial-lichen crusts differed significantly among five desert habitats. Environmental and biocrust development variables explained bacterial community variation better than geographic distance, suggesting a weaker influence of dispersal limitation on the bacterial communities in biocrusts. In addition, the distance-decay rate was higher at the slope than that at the landscape scale, suggesting a fast turnover rate of bacterial community communities induced by topography. Our study implies that soil attributes and biocrust development have more profound impacts on soil bacterial communities than precipitation, which provides novel insights into the geographical distribution and assemblage of soil bacterial communities in deserts. Moreover, our study is significant with respect to understanding the potential responses of soil microbial communities to climate change in desert areas under the scenario of increasing precipitation variation.

    更新日期:2020-01-21
  • Distinct regulation of microbial processes in the immobilization of labile carbon in different soils
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-18
    Xinxin Wang; Wei Zhang; Feng Zhou; Yan Liu; Hongbo He; Xudong Zhang

    A process-based understanding of soil carbon (C) sequestration and stabilization has not been precisely characterized due to the lacking of linkage between microbial proliferation and mortality. In this study, stable isotope probing of phospholipid fatty acids and amino sugars were used to determine the microbial responses and microbial residue retention in two soils (Mollisol and Ultisol) with 13C-labeled glucose addition. The microbial responses stimulated by glucose were greater in C-poor Ultisol than in C-rich Mollisol. However, the transformation of labile C to microbial residues in Mollisol was more rapid. Therefore, the starvation effect may control microbial growth and microbial residue production, and thus resulting in distinct sequestration and stabilization process of labile C in different soils.

    更新日期:2020-01-21
  • Carbon and nitrogen recycling from microbial necromass to cope with C:N stoichiometric imbalance by priming
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-17
    Jun Cui; Zhenke Zhu; Xingliang Xu; Shoulong Liu; Davey L. Jones; Yakov Kuzyakov; Olga Shibistova; Jinshui Wu; Tida Ge

    The impact of increasing amounts of labile C input on priming effects (PE) on soil organic matter (SOM) mineralization remains unclear, particularly under anoxic conditions and under high C input common in microbial hotspots. PE and their mechanisms were investigated by a 60-day incubation of three flooded paddy soils amended with13C-labeled glucose equivalent to 50–500% of microbial biomass C (MBC). PE (14–55% of unamended soil) peaked at moderate glucose addition rates (i.e., 50–300% of MBC). Glucose addition above 300% of MBC suppressed SOM mineralization but intensified microbial N acquisition, which contradicted the common PE mechanism of accelerating SOM decomposition for N-supply (frequently termed as “N mining”). Particularly at glucose input rate higher than 3 g kg−1 (i.e., 300–500% of MBC), mineral N content dropped on day 2 close to zero (1.1–2.5 mg N kg−1) because of microbial N immobilization. To cope with the N limitation, microorganisms greatly increased N-acetyl glucosaminidase and leucine aminopeptidase activities, while SOM decomposition decreased. Several discrete peaks of glucose-derived CO2 (contributing >80% to total CO2) were observed between days 13–30 under high glucose input (300–500% of MBC), concurrently with CH4 peaks. Such CO2 dynamics was distinct from the common exponential decay pattern, implicating the recycling and mineralization of 13C-enriched microbial necromass driven by glucose addition. Therefore, N recycling from necromass was hypothesized as a major mechanism to alleviate microbial N deficiency without SOM priming under excess labile C input. Compound-specific 13C-PLFA confirmed the redistribution of glucose-derived C among microbial groups, i.e., necromass recycling. Following glucose input, more than 4/5 of total 13C-PLFA was in the gram-negative and some non-specific bacteria, suggesting these microorganisms as r-strategists capable of rapidly utilizing the most labile C. However, their 13C-PLFA content decreased by 70% after 60 days, probably as a result of death of these r-strategists. On the contrary, the 13C-PLFA in gram-positive bacteria, actinomycetes and fungi (K-strategists) was initially minimal but increased by 0.5–5 folds between days 2 and 60. Consequently, the necromass of dead r-strategists provided a high-quality C–N source to the K-strategists. We conclude that under severe C excess, N recycling from necromass is a much more efficient microbial strategy to cover the acute N demand than N acquisition from the recalcitrant SOM.

    更新日期:2020-01-21
  • The fertile island effect collapses under extreme overgrazing: evidence from a shrub-encroached grassland
    Plant Soil (IF 3.259) Pub Date : 2020-01-15
    Yurong Cai, Yuchun Yan, Dawei Xu, Xingliang Xu, Chu Wang, Xu Wang, Jinqiang Chen, Xiaoping Xin, David J Eldridge

    Woody plant encroachment is a phenomenon of global concern in drylands due to demonstrated reductions in livestock carrying capacity. However, shrubs are known to contribute to the development of patches of enhanced fertility that might offset any negative effects of increasing grazing. We measured soil physical and chemical characteristics within shrub and open patches across a gradient in livestock grazing to explore how the relative effect of shrubs might change with increasing grazing-induced disturbance.

    更新日期:2020-01-15
  • Development Of A Soil Quality Index For Characterizing Effects Of Land Use Changes On Degradation And Ecological Restoration Of Rangeland Soils In A Semi‐Arid Ecosystem
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-14
    Fayez Raiesi; Soroosh Salek‐Gilani

    The aim of this research was to study the influence of land use‐changes on degradation and ecological restoration of rangeland soils by quantifying fifteen soil attributes and the subsequent development of a soil quality index (SQI). Soil properties were determined to establish a minimum data set (MDS) for the development of an overall weighted additive SQI. The soil attributes were measured on samples (0–15 and 15–30 cm depths) collected in undisturbed rangelands, cultivated rangelands and restored rangelands following cultivation abandonment for 12 or 45 years in a semi‐arid ecosystem, Central Iran. The selected MDS indicators consisted of the mean‐weight diameter (MWD), total nitrogen (TN), microbial respiration (MR), and alkaline phosphomonoesterase activity (ALP). Overall, soil aggregation, N content, microbial activity, and ALP activity were found to be the key indicators contributing considerably to the SQI of rangeland ecosystems. Soil MWD had the highest contribution (31%) to the estimated SQI values, followed by TN (27%), MR (22%) and ALP (21%). Results indicated a clear difference in soil quality among the common land uses with a significant decline of SQI after conversion of native rangelands (0.80) to croplands (0.53). Restored rangeland soils were characterized by a higher value of SQI (0.63–0.73) as compared with cultivated rangelands (0.53). This suggests a good recovery of soil capacity and functions after the abandonment of cropping activity in previously cultivated rangelands. Vegetation restoration and plant productivity appeared to be the major driver of improved soil quality of the abandoned croplands in these rangelands. A soil quality assessment tool would be useful to determine the success of agricultural abandonment and ecological restoration of rangeland soils in the studied semi‐arid environment.

    更新日期:2020-01-14
  • Soil bacteria and fungi respond differently to plant diversity and plant family composition during the secondary succession of abandoned farmland on the Loess Plateau, China
    Plant Soil (IF 3.259) Pub Date : 2020-01-14
    Zekun Zhong, Xinyi Zhang, Xing Wang, Shuyue Fu, Shaojun Wu, Xuqiao Lu, Chengjie Ren, Xinhui Han, Gaihe Yang

    Abstract Aims This study aimed to determine the responses of soil bacteria and fungi to plant species diversity and plant family composition (PFC) following secondary succession on former farmland (FL). Methods Illumina sequencing of 16S rRNA and ITS genes was used to determine soil microbial communities along a chronosequence of FL left abandoned for 0, 10, 20, 30, 40, and 50 years on the Loess Plateau. Soil properties, plant diversity, and PFC were also investigated. Results Fungal communities were dominated by Ascomycota and Basidiomycota. Fungal diversity and Ascomycota abundance increased with time, while Basidiomycota abundance decreased. The fungal diversity and dominant phyla were related to the increasing levels of plant species diversity and evenness with succession. Bacterial diversity first increased and then decreased as succession proceeded, peaking at 30 years. Bacterial communities transitioned from Actinobacteria to Proteobacteria dominance during the first 30 years, after which Actinobacteria was dominant. Plant family composition exerted indirect effects on the diversity and dominant phyla of bacterial communities, mainly through direct effects on soil organic carbon and total nitrogen content. Bacterial diversity and Proteobacteria abundance were higher at Leguminosae- and Gramineae-dominant succession stages, but lower in Compositae-dominant plots; Actinobacteria showed the opposite result. Conclusions Plant species diversity and evenness might be the key drivers for shaping fungal communities, but bacteria are influenced more by changes in PFC and abiotic soil nutrient levels during succession.

    更新日期:2020-01-14
  • NAC transcription factors from Aegilops markgrafii reduce cadmium concentration in transgenic wheat
    Plant Soil (IF 3.259) Pub Date : 2020-01-14
    Xuye Du, Fang He, Bin Zhu, Mingjian Ren, Heng Tang

    Abstract Background and aims Cadmium (Cd) is one of the heavy metal elements that are most harmful to human health, and the transmission of Cd through the food chain is a global issue. Aegilops markgrafii is a wild relative of the cultivated wheat that is tolerant of high levels of Cd. The objective of this study is to investigate the NAC transcription factors (TFs) involved in Cd tolerance in Ae. markgrafii and to verify their function in transgenic wheat. Methods We cloned NAC TFs from Ae. markgrafii plants exposed to excessive Cd treatment. The expression profiles of NAC TFs in root and shoot tissues were examined using qRT-PCR. Transgenic wheat was obtained via Agrobacterium-mediated transformation. Finally, we examined Cd concentrations in transgenic wheat under excess Cd treatment. Results We identified three NAC TFs and classified them into four subfamilies. Sequence alignments showed that the NAC TFs had conserved N-terminal domains but varied C-terminal domains. Expression profiles of NAC TFs showed about 150-fold up-regulation in the transcription of AemNAC2 and AemNAC3 under excess Cd treatment. Overexpression of AemNAC2 in the wheat cultivar ‘Bobwhite’ led to reduce Cd concentration in the root, shoot and grains. Conclusions AemNAC2 is an important TF that contributes to Cd tolerance in wheat.

    更新日期:2020-01-14
  • Translocating subtropical forest soils to a warmer region alters microbial communities and increases the decomposition of mineral-associated organic carbon
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-14
    Xiong Fang; Guoyi Zhou; Chao Qu; Wenjuan Huang; Deqiang Zhang; Yuelin Li; Zhigang Yi; Juxiu Liu

    It is not clear how soil organic carbon (SOC) and its related microbial processes respond to climate warming in subtropical forest, which limits our ability to predict the response and feedback of such forests to future warming. Here, we translocated a forest microcosm from a high-elevation site to a low-elevation site (600 m–30 m a.s.l.) in a subtropical forest, to study the responses of SOC fractions, microbial communities and enzyme activities to increases in soil temperature (ca. 1.69 °C). Results showed that translocation to a warmer region significantly decreased the total SOC content by an average of 21.1% after three years of soil warming. Warming non-significantly decreased the particulate organic C (POC) and microbial C (MBC) content by 15.7% and 15.2%, respectively, and increased the light fraction organic C (LFOC) and dissolved organic C (DOC) content by 15.5% and 2.3%, respectively. By contrast, warming significantly decreased the <53 μm fraction organic C (N-POC, −15.3%) and heavy fraction organic C (HFOC, −14.8%) content. Warming significantly decreased the relative abundance of total bacteria (−2.7%), G+ bacteria (−6.1%), G− bacteria (−6.6%) and actinomycetes (−10.8%), but increased the relative abundance of fungi (+22%). The oxidase and mass-specific oxidase activities were significantly increased by 32–70% in the warming soils. The decline in the N-POC was highly correlated to the increases in the relative abundance of fungi, the ratio of fungal to bacterial biomass (F:B), oxidase and mass-specific oxidase activities. Our results suggest that climate warming may increase the potential for fungal decomposition of mineral-associated organic C by increasing oxidase activities, leading to greater C losses in the subtropical forest than previously estimated.

    更新日期:2020-01-14
  • Nitrogen addition has contrasting effects on particulate and mineral-associated soil organic carbon in a subtropical forest
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-14
    Jungang Chen; Wen Xiao; Chengyang Zheng; Biao Zhu

    Increasing atmospheric nitrogen (N) deposition has substantially affected carbon (C) and nutrient cycling in forest ecosystems. However, the responses of different soil organic carbon (SOC) fractions with different turnover rates to N addition are highly divergent, and the underlying mechanisms remain elusive. In this study, we explored the responses of surface soil (0–10 cm) characteristics and microbial communities to six years of experimental N addition (0, 50, 100 and 150 kg N ha−1 yr−1) in a subtropical evergreen broadleaf forest in southern China. Our results showed that N addition led to significant soil acidification (pH from 5.3 to 4.9). Microbial biomass carbon and total microbial, bacterial and fungal abundance (phospholipid fatty acid, PLFA) were reduced by N addition, but extracellular enzymes involved in C, N and phosphorus (P) cycling were not responsive to N addition. Soil extractable Ca2+ concentration was depleted by N addition, while other extractable cations (Fe3+, Al3+, Mg2+, K+, Na+) were not affected. Moreover, N addition did not significantly change the C and N concentration of bulk soil. We further separated the bulk soil into particulate organic matter (>53 μm, POM) and mineral-associated organic matter (<53 μm, MAOM) fractions by wet sieving. Interestingly, C in the POM fraction was significantly increased by N addition, while C in the MAOM fraction was depleted by N addition. Correlation analysis and structural equation modeling results suggested that N addition may suppress microbial decomposition of plant inputs and thus lead to accumulation of C in the POM fraction, while it may reduce the mineral sorption of microbial necromass and products and thus cause depletion of C in the MAOM fraction. Taken together, our results highlighted the vulnerability of soil C in the stable MAOM fraction to N addition, and emphasized the role of soil metals (particularly extractable Ca2+) and pH in controlling soil C storage under N addition.

    更新日期:2020-01-14
  • Spatio‐temporal changes in the understory heterogeneity, diversity, and composition after fires of different severities in a semiarid oak (Quercus brantii Lindl.) forest
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-13
    Mehdi Heydari; Hadieh Moradizadeh; Reza Omidipour; Arash Mezbani; David Pothier

    In arid and semiarid forests and rangelands, native ranchers and farmers frequently use fire as a tool to improve soil fertility and vegetation composition, and to facilitate soil tilling. Investigating changes in ecosystem characteristics after these measures is of great importance for establishing management and recovery strategies. This study aimed to investigate spatial–temporal changes in the understory heterogeneity, diversity and composition after fires of different severities in a Brant's oak (Quercus brantii Lindl.) forest. Vegetation sampling was monitored in 14 patches including unburned sites (UBN), burned sites with low fire severity after 1, 5, and 10 years (LFSO, LFSF, and LFST, respectively), and burned sites with high fire severity after 1, 5, and 10 years (HFSO, HFSF, and HFST, respectively). Fire severity and time since fire significantly affected diversity indices with the lowest values of richness, evenness and diversity in high‐severity fires, while the highest values were observed in low‐severity fires. Time since fire did not significantly affect the understory evenness in both fire severities. However, species diversity and richness in low‐severity fires decreased with time since fire while the reverse was observed in high‐severity fires. The results of a detrended correspondence analysis indicated that the severity and time since fire significantly changed vegetation composition. The largest changes in vegetation composition compared to control sites were observed in HFSO, and then in HFSF and HFST. Both fire severity and time since fire caused changes in the heterogeneity of plant communities. We concluded that the use of low‐severity fires can be suitable for maintaining and increasing the heterogeneity of understory vegetation in semiarid forest ecosystems. However, low‐severity fires have also slightly, while not significantly, increased evenness and can therefore potentially reduce the ecosystem functions of dominant species in such semiarid regions. This could mitigate the positive effect of fire on vegetation heterogeneity and necessitate further investigations.

    更新日期:2020-01-13
  • Monitoring soil organic carbon in alpine soils using in situ vis‐NIR spectroscopy and a multilayer perceptron
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-13
    Songchao Chen; Dongyun Xu; Shuo Li; Wenjun Ji; Meihua Yang; Yin Zhou; Bifeng Hu; Hanyi Xu; Zhou Shi

    Soil quality in alpine ecosystems requires regular monitoring to assess its dynamics under changes in climate and land use. Visible near‐infrared (vis‐NIR) spectroscopy could offer an option, as sampling and transporting large numbers of soil samples in the Qinghai‐Tibet Plateau is extremely difficult. However, the potential for in situ vis‐NIR spectra and the optimal algorithms need to be defined in this region. We have therefore evaluated the performance of a deep learning method, multilayer perceptron (MLP), for in situ spectral measurement of soil organic carbon (SOC) with in situ vis‐NIR spectroscopy in southeastern Tibet, China. A total of 39 soil cores (maximum depth 1 m), including 547 soil samples taken from each 5‐cm depth interval, were collected. The spectra were also measured at each 5‐cm depth interval accordingly. After spectral preprocessing, 4,096 MLP models were generated by taking all the combinations from six parameters defined in the MLP. The 10‐fold‐core cross‐validation showed that MLP had a good performance for in situ SOC prediction, and the best MLP model had an R2 of .92, which were much better than those of the partial least squares regression model (R2 = .80). The results also suggested that the number of epochs, number of neurons, and dropout rate were the most important parameters in the MLP model. We concluded that in situ vis‐NIR spectroscopy coupled with an MLP model has high potential for large‐scale SOC monitoring in the Qinghai‐Tibet Plateau. Our results also provide a reference for rapid hyperparameter optimization using MLP for future soil spectroscopic modeling.

    更新日期:2020-01-13
  • Soil organic carbon sequestration and its stability after vegetation restoration in the Loess Hilly Region, China
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-12
    Hongwei Xu; Qing Qu; Minggang Wang; Peng Li; Yuanze Li; Sha Xue; Guobin Liu

    Vegetation restoration is widely recognized as a way to improve soil organic carbon (SOC) stock. However, whether these recovered carbons are stable is yet largely uncertain. Thus, we determined the sequestration and stability of SOC in soils with three different types (Caragana korshinskii (CA) aged for 10, 20, 36, and 47 years, Hippophae rhamnoides (HR) aged for 5, 10, 20, and 30 years, and Robinia pseudoacacia (RP) aged for 5, 10, 20, 37, and 56 years) to compare their SOC sequestration and stability in different depths in this study. The SOC content, SOC stock, very labile fraction of oxidizable carbon (C1), labile fraction of oxidizable carbon (C2), and carbon management index (CMI) in 0–30 cm depths of the three types increased over the chronosequence. The SOC stocks increased by 1.40–3.19 Mg ha−1 in CA during the 47‐year restoration, by 5.76–10.01 Mg ha−1 in HR during the 30‐year restoration and by 1.88–8.93 Mg ha−1 in RP during the 56‐year restoration, respectively, in 0–30 cm depths. The carbon stability index (SI) in 0–10 cm depth of CA, 0–30 cm depths of HR, and 0–50 cm depths of RP decreased with recovery time. Over the recovery time, SOC content, SOC stock, CMI, and SI were lower than those of nature forest (NF aged more than 100 years) in all restored sites at the later stage of recovery. SOC sequestration decreased, but its stability increased, with the soil depths. Overall, HR had a higher SOC sequestration rate and lower SI (0–30 cm) than CA and RP. Our results revealed that although the SOC sequestration appears enhanced over the restoration, but the SOC stability becomes lower, so that the recovery of these site to the level of NF may meet difficulties in this semiarid Loess Hilly Region.

    更新日期:2020-01-13
  • Cropland abandonment altered grassland ecosystem carbon storage and allocation and soil carbon stability in the Loess Hilly Region, China
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-10
    Hongwei Xu; Xiukang Wang; Qing Qu; Jiaying Zhai; Yahui Song; LeiLei Qiao; Guobin Liu; Sha Xue

    Determining changes in grassland ecosystem carbon (C) storage and soil C stability after cropland abandonment is important for estimating the regional C budget and global C cycle. However, the understanding of ecosystem C storage and allocation and soil C stability along the grassland restoration chronosequence is insufficient. Thus, grasslands with different recovery years (0, 2, 5, 8, 11, 15, 18, 26, and 30 years) were chosen to monitor the dynamics of grassland ecosystem C storage, vegetation biomass C storage, soil C storage, and soil C stability in different soil depths, as well as a natural grassland (NG) reference. The results showed that aboveground biomass (AGB), belowground biomass (BGB), soil C storage, ecosystem C storage, the very labile fraction of oxidizable C (C1) (0–0.3 m layers), the labile fraction of oxidizable C (C2) (0–0.3 m layers), and the C management index increased with the recovery years. The vegetation species richness (R), vegetation species evenness (E), and vegetation species diversity (H′) initially increased, peaking at 18a and then decreasing with recovery years, but the soil C stability index (SI) at 0–0.3 m decreased over time. Additionally, the AGB, BGB, litter biomass (LB), R, H′, ecosystem C storage, and SI (0–0.3 m and 0.5–1.0 m layers) of 30‐year grassland (GL30) showed no significant differences relative to those found in the NG. Furthermore, the soil C sequestration rate decreased with decreasing soil depth, while the soil C stability increased. These results suggest an optimistic outlook for the recovery of ecosystem C, but the soil C under these conditions is unstable, posing a risk to soil C sequestration in abandoned cropland on the Loess Plateau without appropriate management.

    更新日期:2020-01-13
  • Soil microbiotic homogenization occurred after long‐term agricultural development in desert areas across northern China
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-10
    Jie Liu; Aiai Xu; Changkun Wang; Zhiying Guo; Shiwen Wu; Kai Pan; Fangfang Zhang; Xianzhang Pan

    Soil microbial communities respond significantly to long‐term agricultural development in desert areas. Because soil microbial communities are distinct in various deserts at different eco‐climate regions, their response patterns to agricultural development are diverse at a local scale. However, whether the different response patterns had some commonalities across various types of deserts at a larger spatial scale remained unclear. To address this question, historical soil samples, collected in different years from pairwise long‐term experimental plots (desert and farmland) at five field stations of the Chinese Ecosystem Research Network across northern China, were analyzed through high‐throughput sequencing approach. Here, we found that soil bacterial communities were sharply different between deserts and agricultural lands. Contrasting to desert soils with higher relative abundances of Actinobacteria and Firmicutes, agricultural soils harbored higher relative abundances of Proteobacteria, Acidobacteria, and Planctomycetes and exhibited higher bacterial α‐diversity with less variation. More importantly, higher community similarities were found in agricultural lands for each station and all stations, suggesting that soil microbiotic homogenization occurred at both local and regional scales after long‐term agricultural development in desert areas. Further analyses revealed that the homogenization was due to the loss of desert‐endemic species and the range expansion of generalist species, which might result from the introduction of crops combined with agricultural practices. The soil microbiotic homogenization associated with the loss of endemic species should be paid special attention to because this might imply the decrease in ecological resilience to perturbations and might lead to rapid desertification in desert margin areas.

    更新日期:2020-01-13
  • Impacts of future climate and land use change on water yield in a semi‐arid basin in Iran
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-13
    Bagher Shirmohammadi; Arash Malekian; Ali Salajegheh; Bahram Taheri; Hosein Azarnivand; Ziga Malek; Peter H Verburg

    Studying the interaction between hydrology, land use and climate change is necessary to support sustainable water resources management. It is unknown how land management interventions in dry climate conditions can benefit water yield in the context of climate and land use change interactions. In this study, we assessed the effects of both land use and climate change on the Mordagh Chay basin water yield using the Integrated Valuation Ecosystem Service and Tradeoffs model (InVEST). First, we modelled the current water yield, followed by developing six combined climate‐land use scenarios until 2030 based on the CCSM4 climate model for the RCP4.5 and RCP8.5 scenarios. We used three future land use scenarios simulated by the Dyna‐CLUE model. The trend scenario of land use change, which does not include any improvements in irrigation efficiency, significantly affected basin water yield under both climate scenarios. Water yield decreases by 19.8% and 31.8% for the RCP4.5 and RCP8.5, respectively. Under all land use scenarios that included improvements in irrigation efficiency the water yield responded positively. For the RCP4.5 scenario, the water yield was projected to increase between 16.6 and 18% depending on the land use scenario. The increase in water yield under the RCP8.5 climate scenario was much lower than for the RCP4.5 scenario (about one third). Overall, the results showed that by adopting appropriate irrigation efficiency, it is possible to achieve a better balance between environmental needs, regional economic and agricultural development. The results provide insight into possible sustainable development options and also provide guidance for managing the other Urmia Lake sub‐basins while the approach of integrated assessment of climate, land use change and land management options is also applicable in other conditions to help inform sustainable management.

    更新日期:2020-01-13
  • Cytokinin dynamics in xylem sap and leaves of fruiting and de-fruited sunflower hybrids of contrasting post-anthesis canopy senescence patterns during flowering and grain-filling
    Plant Soil (IF 3.259) Pub Date : 2020-01-13
    Mariano A. Mangieri, Antonio J. Hall, Claudio A. Chimenti

    To determine whether xylem sap and leaf cytokinin levels were associated with live root length density (LRLD) and leaf senescence, these variables were measured in intact (control) plants and those from which florets were removed, in hybrids of contrasting post-anthesis senescence patterns.

    更新日期:2020-01-13
  • Intercropping with wheat suppressed Fusarium wilt in faba bean and modulated the composition of root exudates
    Plant Soil (IF 3.259) Pub Date : 2020-01-11
    Jiaxing Lv, Yan Dong, Kun Dong, Qian Zhao, Zhixian Yang, Ling Chen

    The causal agent of Fusarium wilt in faba bean is Fusarium oxysporum f. sp. fabae (FOF), which significantly reduces the yield in continuous cropping systems. We aimed to evaluate the role of wheat in alleviating Fusarium wilt in faba bean.

    更新日期:2020-01-13
  • Induced systemic resistance - like responses elicited by rhizobia
    Plant Soil (IF 3.259) Pub Date : 2020-01-11
    María Laura Tonelli, María Soledad Figueredo, Johan Rodríguez, Adriana Fabra, Fernando Ibañez

    Rhizobia are soil bacteria that engage into a mutualistic symbiosis with plants and benefit the host by fixing atmospheric N. In addition, rhizobia can be considered as biocontrol agents, contributing to plant health through direct inhibition of a wide range of pathogens. More recently, it became evident that rhizobial invasion of plant roots can also trigger an increased systemic resistance state in the host, a process resembling the Induced Systemic Resistance (ISR) mechanism. However, this indirect biocontrol property of rhizobia was relatively less explored.

    更新日期:2020-01-13
  • No-till increases soil denitrification via its positive effects on the activity and abundance of the denitrifying community
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-11
    Jinyang Wang; Jianwen Zou

    Shifting from conventional tillage to a no-till system can contribute to improving soil carbon sequestration and sustaining crop productivity. However, our understanding of the soil nitrogen (N) process through insights into the no-till effect on soil denitrification remains elusive. Here, we compiled data from 323 observations in 57 studies and quantified the responses of soil denitrification and the size and activity of the denitrifying community to no-till vs. conventional tillage. Across all studies, no-till significantly increased soil denitrification (85%) compared to conventional tillage. The no-till effect on soil denitrification was significantly dependent upon N fertilizer management, with a greater increase with N fertilization than without (101 vs. 46%). The increased soil denitrification under no-till was attributed to increases in the size and activity of the denitrifying community. On average, the potential denitrification activity, the total number of denitrifiers, and the abundance of denitrifying genes were increased by 66, 116, and 14–70%, respectively, in response to no-till. Our results demonstrate that soil denitrification under no-till leads to increased soil nitrous oxide (N2O) emission. This is supported by a larger response of soil N2O emission compared to the total denitrification, together with a significant increase (33%) in the (nirK + nirS)/nosZ ratio under no-till conditions. Therefore, the increased soil denitrification under no-till conditions may have negative impacts on soil N cycling and mitigation of N2O emission.

    更新日期:2020-01-13
  • Ecological clusters based on responses of soil microbial phylotypes to precipitation explain ecosystem functions
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-11
    Ying Wu; Jianping Wu; Muhammad Saleem; Bing Wang; Shuijin Hu; Yongfei Bai; Qingmin Pan; Dima Chen
    更新日期:2020-01-13
  • Accumulation and partitioning of rare earth elements in olive trees and extra virgin olive oil from Adriatic coastal region
    Plant Soil (IF 3.259) Pub Date : 2020-01-10
    Filip Pošćić, Mirella Žanetić, Željka Fiket, Martina Furdek Turk, Nevenka Mikac, Niko Bačić, Mavro Lučić, Marija Romić, Helena Bakić, Maja Jukić Špika, Branimir Urlić, Marko Runjić, Gabriela Vuletin Selak, Elda Vitanović, Tatjana Klepo, Jakša Rošin, Zed Rengel, Slavko Perica

    A potential of rare earth elements (including yttrium) (REY) accumulation in olives is increasing due to enhanced use of REY in human activities. REY transfer to extra virgin olive oil (EVOO) is little studied, and characterising the relationships between soil properties and REY concentrations in olive leaves, pomace and EVOO can enhance our understanding of soil-plant interactions.

    更新日期:2020-01-11
  • Plant uptake of nitrogen and phosphorus among grassland species affected by drought along a soil available phosphorus gradient
    Plant Soil (IF 3.259) Pub Date : 2020-01-10
    Pierre Mariotte, Tom Cresswell, Mathew P. Johansen, Jennifer J. Harrison, Claudia Keitel, Feike A. Dijkstra

    Here we assessed N and P uptake of four grassland species grown together in response to a short-term drought event along a soil P gradient.

    更新日期:2020-01-11
  • Solidago canadensis invasion in abandoned arable fields induces minor changes in soil properties and does not affect the performance of subsequent crops
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-09
    Szymon Zubek; Marta L. Majewska; Paweł Kapusta; Anna M. Stefanowicz; Janusz Błaszkowski; Katarzyna Rożek; Małgorzata Stanek; Filip Karpowicz; Joanna Zalewska‐Gałosz

    The global fast‐growing presence of invasive species requires urgent action to assess their ecological and economic impact. Although a number of recent works have shown that alien plant invasions can affect native plant communities, soil microbial communities, and soil physicochemical properties, rarely the effects of invaders on all these parameters have been examined at once. Moreover, no studies have focused on the effects of invasive plants on the ecosystem services after the removal of invaders. For this study, Solidago canadensis, one of the most successful global invasive species, was chosen. In the first stage, invasion‐induced changes in plant community and soil properties in abandoned arable fields were assessed. In the second stage, the effects of these changes on crops, Helianthus annuus and Zea mays, were assessed in a laboratory soil‐feedback experiment. The invader reduced substantially the richness and cover of native plant species. It had little impact on soil physicochemical and microbiological properties: Soil moisture was lower, whereas mycorrhizal parameters and urease activity were higher in invaded plots. The experiment revealed minor and inconsistent effects of the invader: It affected the mycorrhizal colonization and shoot mass of crop plants, but the direction of changes depended on the origin of the soil used. In conclusion, although S. canadensis invasion clearly displaces native vegetation, it has few and rather weak effects on soil properties that did not affect the performance of subsequent crops. The results are promising from the viewpoint of restoring the agricultural function to abandoned fields invaded by S. canadensis.

    更新日期:2020-01-11
  • Effect of cushion plants on the soil seed bank in overgrazed semiarid regions
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-09
    Reza Erfanzadeh; Shadi Hazhir; Mohammad Jafari

    Evaluation of soil seed bank (SSB) in relation to biotic environmental factors could be important in degraded areas, since SSB is one of the major sources that facilitates the recovery of degraded plant communities after disturbances such as grazing, flooding and drought. The aim of this study was to investigate the role of Astragalus myriacanthus and Acantholimon spinosum on SSB characteristics. Soil sampling was carried out in four different positions (upslope edge, downslope edge, center and outside) of each cushion in semiarid mountainous regions in Iran. Then, SSB composition and density, species diversity and richness of SSB in each position were estimated using the germination method. The results of the nonmetric multidimensional scaling showed that the separation of species composition of SSB in four different positions was not possible in any of the cushion species. Nevertheless, the results indicated that the lowest of SSB density, species diversity and richness were observed in the outside of the two cushions. In both cushions, A. myriacanthus and A. spinosum, the mean SSB density (1,606.4 and 646.5 seeds/m2, respectively) was significantly higher in the upslope edge. Totally, the mean density of SSBs in A. myriacanthus (903.6 seeds/m2) was significantly higher than that of A. spinosum (360.6 seeds/m2). We concluded that the cushion plants can act as seed traps and therefore could facilitate recovery of degraded sites in the steep‐hilly areas, while, the possibility of seed penetration into the soil of different directions of cushion might be significant.

    更新日期:2020-01-11
  • The impact of coastal flooding on agriculture: a case study of Lincolnshire, United Kingdom
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-10
    Iain J Gould; Isobel Wright; Martin Collison; Eric Ruto; Gary Bosworth; Simon Pearson

    Under future climate predictions the incidence of coastal flooding is set to rise. Many coastal regions at risk, such as those surrounding the North Sea, comprise large areas of low‐lying and productive agricultural land. Flood risk assessments typically emphasise the economic consequences of coastal flooding on urban areas and national infrastructure. Impacts on agricultural land have seen less attention, and considerations tend to omit the long term effects of soil salinity. The aim of this study is to develop a universal framework to evaluate the economic impact of coastal flooding to agriculture. We incorporated existing flood models, satellite acquired crop data, soil salinity and crop sensitivity to give a novel and detailed assessment of salt damage to agricultural productivity over time. We focussed our case study on low‐lying, highly productive agricultural land with a history of flooding in Lincolnshire, UK. The potential impact of agricultural flood damage varied across our study region. Assuming typical cropping does not change post‐flood, financial losses range from £1,366/ha to £5,526/ha per inundation; these losses would be reduced by between 35% up to 85% in the likely event that an alternative, more salt‐tolerant, cropping, regime is implemented post‐flood. These losses are substantially higher than loses calculated on the same areas using established flood risk assessment framework conventionally used for freshwater flood assessments, with differences attributed to our longer term salt damage projections impacting over several years. This suggests flood protection policy needs to consider local and long terms impacts of flooding on agricultural land.

    更新日期:2020-01-11
  • Flood frequency analysis of the forward restoration of the impact of land‐use change based on the HEC‐HMS model
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-10
    Xin Yan; Musheng Lin; Xingwei Chen; Huaxia Yao; Chuanming Liu; Bingqing Lin

    To reveal the impacts of land‐use change on flood frequency distribution, a method to forward restore the largest‐gauged annual flood series to current land‐use conditions was proposed, based on the Hydrologic Engineering Center‐Hydrologic Modelling System (HEC‐HMS), with a newly developed iterative asymptotic method to calibrate the model parameters. Using the Xixi basin on the southeastern coast of China as a case study, the HEC‐HMS model was applied to forward restore the largest annual floods between 1956 and 2011 by using the land‐use conditions of 2010. The flood peak flow series derived from forward restoration were used for flood frequency analysis. The results showed that (1) the iterative asymptotic method could calibrate the initial loss ratio and wave velocity relatively well. The physical meaning of the parameter values obtained was clear. The overall model simulation result was satisfactory, with Nash–Sutcliffe efficiency coefficients of 0.827 and 0.843 in the calibration and verification periods, respectively. (2) The calibration method effectively addressed the difficulty in determining the model parameters needed for resolving the restoration of the impacts of land‐use changes on the largest‐gauged annual flood peak flows and provided a newer HEC‐HMS‐based restoration approach for non‐stationary flood frequency analysis. (3) Urbanization in the Xixi basin caused a degradation in forested and arable lands, as well as in grasslands. Its main impact on the flood frequency distribution was that the average flood peak flow increased from 2633.32m3/s to 2889.48m3/s, and the changes in the coefficient of variation and coefficient of skewness were very small.

    更新日期:2020-01-11
  • The mobility of arsenic from highly polluted farmlands to wheat: soil‐plant transfer model and health risk assessment
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-10
    Kamaladdin Karimyan; Mahmood Alimohammadi; Afshin Maleki; Masud Yunesian; Ramin Nabizadeh Nodehi; Abbas Rahimi Foroushani

    Arsenic (As) can be transferred from soil and accumulated in food plants. So far, we have a knowledge gap about transference of As from agricultural soils to wheat plant in the natural polluted environment. The aim of present study was to investigate As transfer from soil to different tissues of wheat at a highly As polluted area. In this regard, the mobility indices were used to explain As transfer and accumulation from soil to wheat plant. Moreover, the relationships between soil properties including soil As content, pH, cation‐exchange capacity (CEC), electrical conductivity (EC), organic matter (OM), Fe and Al percentage with As concentrations in wheat root, straw and grain were investigated. Finally, the potential health risks of As exposure to humans through consumption of the local wheat crops were assessed. According to the results, harmful degree of As were accumulated in different parts of wheat plant. The impact of different soil properties on As accumulation in wheat were found to be as follows: soil As content > Al % > Fe % > OM > pH > CEC > EC. High carcinogenic and non‐carcinogenic risks in all age groups of consumers were found. The minimum and maximum values for target hazard quotient (THQ) and excess lifetime cancer risk (ELCR) were found to be 1.22, 102.97 and 0.000061, 0.33, respectively. These findings strongly support the notion that As can be entered to food chain through agricultural products cultivated in polluted soils.

    更新日期:2020-01-11
  • Engineering rhizobacterial community resilience with mannose nanofibril hydrogels towards maintaining grain production under drying climate stress
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-10
    Falko Mathes; Pandiyan Murugaraj; Jeremy Bougoure; Vy T.H. Pham; Vi K. Truong; Michael Seufert; Alexander H. Wissemeier; David E. Mainwaring; Daniel V. Murphy
    更新日期:2020-01-11
  • New problems of food security in Northwest China: A sustainability perspective
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-08
    Xian Liu; Lijie Shi; Haiyang Qian; Shikun Sun; Pute Wu; Xining Zhao; Bernie A. Engel; Yubao Wang

    China's food security has met standards set by the United Nations Food and Agriculture Organization. However, this development is based on excessive resource input and sacrificing the environment. There are few studies on how to evaluate food production systems with a sustainability framework. In order to guarantee the food security in Northwest China, and realize the sustainable development of agricultural production, this study was carried out. On the basis of comprehensive analysis of new problems faced, including water resources, cultivated land resources and ecological security, several indicators such as water resources development and utilization rate, cultivated land pressure index, cultivated land quality index, N and P emissions and emission intensity are proposed to comprehensively evaluate the sustainability of grain production in Northwest China and put forward countermeasures to realize regional sustainable development. The results show that the water resources are already at a high‐stress level as the development and utilization rate of water resources is 42.7% in 2015. Industrial and domestic water continues to squeeze agricultural water use (annual average reduction of 0.1%). The amount of per capita cultivated land in 2015 has decreased by 9.7% compared to 2000. The quality index of cultivated land is as low as 0.22. A series of ecological problems caused by agricultural production have intensified the ecological crisis in the Northwest, which in turn will further affect food security. Suggestions to address these issues include improving agricultural water use efficiency, strengthening the measures of arable land conservation, improving fertilizer utilization efficiency and reducing plastic‐film mulch residues.

    更新日期:2020-01-09
  • A new grading system for evaluating China's cultivated land quality
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-09
    Liming Liu; De Zhou; Xiao Chang; Zhulu Lin

    Cultivated land is crucial to food security, social and economic stability, environmental quality, and sustainable urban–rural development in China and around the world. However, most of the current grading systems for evaluating cultivated land quality in China tend to generate homogeneous results and inadequate spatial descriptions mainly due to the use of a composite index method that often fails to recognize the matching relationship between land use needs and the quality of cultivated land. The purpose of this study is to propose a new grading system for evaluating China's cultivated land quality that involves two index systems and a scoring and grading scheme. In the proposed system, cultivated land quality is redefined in terms of production capacity quality and environmental quality, and the minimum limiting factor method and the weighted linear model are coupled for factor scoring and grading. The new system is demonstrated by a case study in Yimen Town, a loess plateau region in Western China's Shaanxi Province. The results of this study clearly indicate that the new grading system is superior to the current system when compared using two methods: the spatial pattern comparison method and the crop performance validation method. The results are also favorable in terms of matching relationships between the subclasses of cultivated land quality versus soil types and landforms. The new grading system not only helps to better understand the cultivated land quality but also provides a clear direction for science‐based remediation and amelioration of cultivated land.

    更新日期:2020-01-09
  • Quantifying regional effects of plastic mulch on soil nitrogen pools, cycles, and fluxes in rain‐fed agro‐ecosystems of the Loess Plateau
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-09
    Fei Mo; Juan Han; Xiao‐Xia Wen; Xiu‐Kang Wang; Pu‐Fang Li; Nangia Vinay; Zhi‐Kuan Jia; You‐Cai Xiong; Yun‐Cheng Liao

    Plastic mulch is extensively used to enhance agricultural productivity in the Loess Plateau (LP). However, the effect of mulching on the key processes that dominate soil nitrogen dynamics is rarely assessed quantitatively. We quantified the responses of agro–ecosystem nitrogen–cycling to plastic mulching using a comprehensive database drawn from mulching experiments in the LP. Our results indicated that through increasing the soil mineral and dissolved organic nitrogen concentrations, plastic mulching significantly enhanced the soil nitrogen availability by 36.6% at the regional scale, compared to traditional non‐mulching. Mulching pattern, nitrogen application and soil type were found to be the most significant drivers in determining nitrogen availability. Furthermore, nitrogen gaseous releases and hydrological leaching were significantly reduced by 7.0% and 9.4% respectively, under plastic mulching, which led to an insignificant change in the soil total nitrogen pool. Nitrogen input level and soil organic carbon appeared to be the most important factors influencing soil nitrogen losses. Critically, along with increased root residue inputs to soil and improved water‐thermal under mulching, soil microbial activity was increased significantly. This was indicated by enhanced microbial biomass nitrogen and soil nitrogen–related extracellular–enzyme activity, and was driven by nitrogen input, mulching duration and soil carbon status. We generalize that in the rain‐fed agro–ecosystems of the LP, plastic mulch will have little impact on nitrogen pool size, largely due to reduced gaseous and hydrological nitrogen losses, and increased crop‐sourced nitrogen inputs, but will strongly stimulate microbial growth, metabolism and activities, which consequently will speed up biogeochemical cycles of soil nutrients.

    更新日期:2020-01-09
  • Tourism impact assessment modeling in vegetation density of protected areas using data mining techniques
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-09
    Ali Jahani; Hamid Goshtasb; Maryam Saffariha

    In protected areas (PAs), the lack of tourism impact prediction models on vegetation has not been accurately predicted that is a shortcoming in PA management. Now the main question is how recovery can be accelerated; or which ecological factors are associated with the rehabilitation of vegetation density? We aimed to compare the Multi‐Layer Perceptron (MLP), Radial Basis Function Neural Network (RBFNN) and Support Vector Machine (SVM) models to predict tourism impact on land vegetation density changes. Three old national parks of Iran with diversity in tourist pressure and ecological condition of the site were selected for analyzing. We recorded 12 ecological and tourist variables in 400 sample plots which are classified in topography, plot soil, and tourist pressure factors. We developed the tourism impact assessment model (TIAM) by MLP, RBFNN, and SVM techniques. Comparing to RBFNN and SVM, the MLP model (TIAMMLP) is introduced as the most accurate model in vegetation density changes for tourism impact assessment in PAs. The MLP model represents the highest value of R2 in training (0.969), test (0.806) and all datasets (0.876). Sensitivity analysis proved that the values of the tourist pressure, soil organic matters, soil moisture, soil porosity, and soil EC are respectively as the most significant inputs which influence TIAMMLP in PAs. We concluded that habitats with higher organic matter and moisture in the soil would likely tolerate more tourists’ pressure. The MLP model, as a tool for, PAs managers, is able to predict vegetation density changes under tourism pressure precisely.

    更新日期:2020-01-09
  • Mycorrhizal impacts on root trait plasticity of six maize varieties along a phosphorus supply gradient
    Plant Soil (IF 3.259) Pub Date : 2020-01-09
    Xin-Xin Wang, Hongbo Li, Qun Chu, Gu Feng, Thomas W. Kuyper, Zed Rengel

    Plasticity of plants refers to their ability to produce different phenotypes in different environments. Plants show plasticity aboveground as well as belowground. The influence of the arbuscular mycorrhizal fungal (AMF) symbiosis on root plasticity is poorly known. This study aimed to quantify plasticity of root-system related, morphological, physiological or mycorrhizal traits along a soil phosphorus (P) supply gradient.

    更新日期:2020-01-09
  • Contrasting effects of light, soil chemistry and phylogeny on leaf nutrient concentrations in cave-dwelling plants
    Plant Soil (IF 3.259) Pub Date : 2020-01-09
    Kundong Bai, Yigang Wei, Denan Zhang, Longfei Fu, Shihong Lv, Lili Deng

    Abstract Background and aims The drivers of variations in leaf nutrient concentrations in cave-dwelling plants remain poorly understood. We aimed to explore the effects of light, soil chemistry and phylogeny on leaf nutrient concentrations in cave-dwelling plants. Methods We quantified light availability and sampled top-soils and leaves of the co-existing herbs and ferns in three caves. We used the traditional and phylogenetic comparative methods to determine the effects of light, soil chemistry and phylogeny on leaf nutrient concentrations and the cross-species correlations between leaf nutrients. Results Leaf nutrient concentrations differed little among caves due to the non-significant relationships of leaf nutrient concentrations with light availability and soil nutrient concentrations across caves. The phylogenetic signals in leaf nutrient concentrations were significant for Ca, Mg and N but non-significant for the remaining nutrients. The evolutionary rates of leaf nutrient concentrations tended to increase with decreasing phylogenetic signals and were faster in herbs than ferns. These contrasting degrees of phylogenetic conservatism in leaf nutrient concentrations were best generated by Ornstein-Uhlenbeck models, i.e., stabilizing selection towards an optimum across species for P, K, S, Fe, Mn and Zn or higher optimal concentrations in herbs than ferns for Ca, Mg and N. Strong cross-species correlations between leaf nutrient concentrations such as Ca vs Mg and N vs P were found. Conclusions Leaf nutrient concentrations in cave-dwelling plants showed convergent adaptations to cave environments and presented contrasting degrees of phylogenetic conservatism to produce leaf nutritional diversity for the co-existing herbs and ferns in caves.

    更新日期:2020-01-09
  • Streptomyces sp. LH 4 promotes plant growth and resistance against Sclerotinia sclerotiorum in cucumber via modulation of enzymatic and defense pathways
    Plant Soil (IF 3.259) Pub Date : 2020-01-09
    Bong-Gyu Mun, Won-Hee Lee, Sang-Mo Kang, Sang-Uk Lee, Seok-Min Lee, Dong Yeol Lee, Muhammad Shahid, Byung-Wook Yun, In-Jung Lee

    Abstract Background In the soil ecosystem, microbial diversity exists and these diverse organisms interact with plant roots and influence the physicochemical properties of plants. Some of these diverse microorganisms can cause diseases or can provide beneficial interactions with plants. Rhizobacteria are well-known beneficial microorganism that colonize the plant root zone (rhizosphere) and are referred to as plant growth-promoting rhizobacteria (PGPR) that contribute to the promotion of plant growth either directly or indirectly. PGPRs are also known for their biocontrol abilities. Sclerotinia sclerotiorum, an Ascomycetous soil inhabiting fungus, causes white rot disease in cucumbers. This disease results in the loss of millions of dollars annually. The current study was conducted to isolate naturally occurring soil inhabiting bacteria that may promote plant growth under diseased conditions and also antagonize the pathogen. Scope The isolated LH4 strain was identified as Streptomyces sp. by 16S rRNA sequencing and phylogenetic analysis. The plant growth promoting effects and the antifungal antagonistic activities against Sclerotinia sclerotiorum were confirmed by measuring enzymatic activity of LH4 and demonstration in planta. In addition, Streptomyces sp. LH4 pure culture application exhibited significant growth inhibition of S. sclerotiorum in cucumber. Analysis of the major hormones related to pathogen defense; the jasmonic acid, and salicylic acid, showed that the modulation of these two hormones increased disease resistance in cucumber. Conclusion The present study suggests a possible dual role of Streptomyces sp. LH4 as functional material for bio-fertilizer and biocontrol against pathogens.

    更新日期:2020-01-09
  • Soil nitrification increases with elevated phosphorus or soil pH in an acidic mixed mesophytic deciduous forest
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-08
    Jared L. DeForest; Rael K. Otuya

    The role of phosphorus (P) mediating nitrogen (N) transformation processes is poorly understood which raises an important question: Does P, like soil pH, have a strong control in altering the cycling of soil N? From 2010 to 2018, pH and/or P availability was elevated with lime and P fertilizer in three mixed mesophytic deciduous forests on the unglaciated portion of the Allegheny Plateau, southeast Ohio, USA. We hypothesized that in addition to soil pH, P addition can influence the cycling of soil N because both can change N dynamics, which can alter nitrification rates. Increasing soil pH increased nitrification and nitrate pools by 30 and 4 times, respectively during the growing season. Furthermore, elevating P also stimulated nitrification and increased soil nitrate pools by 10 and 2 times, respectively. However, the influence of raising soil pH on nitrification was diminished when combined with P addition. Results suggest that N biogeochemical processes are sensitive to P availability, but the mechanistic nature of this relationship appears complex with unclear feedback systems regulating nitrification rates from these deciduous forests.

    更新日期:2020-01-09
  • Suppression of amino acid and oligopeptide mineralization by organic manure addition in a semiarid environment
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-08
    Shahid Iqbal; Davey L. Jones; Muhammad Saleem Arif; Tahira Yasmeen; Jianchu Xu; Sehroon Khan; Sadia Nadir

    The rapid mineralization of organic nitrogen (ON) in semiarid soils frequently results in large N losses, reduced crop yields, and environmental pollution. The addition of manures to soil has the potential to promote microbial growth, increase N immobilization, reverse the decline in soil organic matter (SOM), and enhance soil quality. In this study, three contrasting organic manures were used to determine their influences on amino acid and oligopeptide dynamics in soil (as key component of the soil ON‐cycle) as well their effects on the size of the microbial biomass and N immobilization. Laboratory incubation experiments were set up with soil obtained from experimental field trial sites for growing maize. Treatments included soil amended with either: poultry‐manure (PM), farmyard‐manure (FYM), pressmud (PrM), or unamended (control). Radio‐ and stable‐isotope (14C‐15N) techniques were used to assess ON mineralization, immobilization, and leaching using the amino acids alanine (Ala) and valine (Val) as well as the oligopeptides trialanine (Ala‐Ala‐Ala) and valine‐proline‐proline (Val‐Pro‐Pro) as model substrates. qPCR was used to determine soil bacterial biomass. The results showed that all manures increased microbial growth and total soil amino acids as well as protein content. Greater immobilization and subsequently lower mineralization and leaching were also observed in the manure‐amended soils, with this being most pronounced in the PM treatment. The application of PM also enhanced the half‐lives of the ON compounds in soil and increased the size of the bacterial biomass. Overall, our findings indicate that manure amendments, particularly PM, can help promote more efficient ON cycling in semi‐arid ecosystem by controlling N mineralization, reducing amino acid leaching, and elevating oligopeptide immobilization.

    更新日期:2020-01-08
  • Soil Bacterial Community Succession During Desertification in a Desert Steppe Ecosystem
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-08
    Miaochun Fan; Jiajia Li; Zhuangsheng Tang; Zhouping Shangguan

    Desertification often occurs in fragile steppe ecosystems, which may lead to severe soil degradation. Understanding how soil microbial communities respond to desertification is critical for ecological restoration of degraded desert steppes. We used an Ion S5™ XL sequencing platform to explore the soil bacterial community succession across four desertification stages in a desert steppe in Ningxia, China. The results showed that soils from potential to light desertification stage had similar physicochemical properties, whereas significantly lower macronutrients, silt, and clay contents and higher pH, moisture, and sand contents were observed in the severe and very severe stages (p < 0.05). Due to change in soil conditions, bacterial communities shifted drastically across the four stages (p < 0.05). Variation in bacterial community composition was driven mainly by the deterministic processes (i.e., habitat filtering based on resource availability and space limitations), but their effects decreased toward the very severe desertification stage. More potential indicator species including members of the genera Nitrosomonas, Pirellula, and Methylobacterium were selected to predict very severe desertification relative to the other three stages. These potential indicators could survive in a wide range of habitats with low availability of carbon and nitrogen sources. Co‐occurrence network analysis revealed that most of soil microorganisms might form symbiotic relationships in response to the habitat heterogeneity caused by desertification. In conclusion, as desertification intensified, distinct shifts in soil bacterial communities were driven primarily by the deterministic processes, which provide new insights for the restoration of degraded habitats and sustainable development of land resources.

    更新日期:2020-01-08
  • Spatial patterns of large‐scale land transactions and their potential socio‐environmental outcomes in Cambodia, Ethiopia, Liberia and Peru
    Land Degrad. Dev. (IF 4.275) Pub Date : 2020-01-08
    Chuan Liao; Suhyun Jung; Daniel G. Brown; Arun Agrawal

    Recent large‐scale land transactions, often framed as “land grabbing,” are historically unprecedented. Millions of hectares of land have changed hands for agriculture‐driven development over the past decade, and their implementation generates substantial risk of land degradation. This paper aims to investigate land transaction patterns and evaluate their potential socio‐environmental impacts in Cambodia, Ethiopia, Liberia, and Peru. We undertake a novel spatially explicit approach to quantify land transactions, and conduct scenario‐based analyses to explore their implementation consequences on people, land, and carbon emission. Our results demonstrate that existing global datasets on land transactions substantially underestimate their incidence, but can either exaggerate or underreport transacted areas. While confirming that land transactions are more likely to occur in sparsely populated, poorer, and more forested areas, our scenario‐based analyses reveal that if fully implemented for agricultural development, land transactions in the four countries will affect more than one million people, yield over 2 Gt of carbon emissions, and disrupt vast swathes of forests. Our findings refute the “empty land” discourse in government policy, and highlight the consequences of land degradation that can occur at an unexpected scale in the “global land rush.” Future policy‐making needs to anticipate the risk of land degradation in terms of deforestation and carbon emission while pursuing agriculture‐driven development through land transactions.

    更新日期:2020-01-08
  • Distinct factors drive the assembly of quinoa-associated microbiomes along elevation
    Plant Soil (IF 3.259) Pub Date : 2020-01-08
    Zhiquan Cai, Xiaobo Wang, Sreetama Bhadra, Qi Gao

    Unravelling the factors shaping microbial community structure across plant holobiont is required to promote plant health and crop productivity.

    更新日期:2020-01-08
  • Rhizodeposition mediates the effect of nitrogen and phosphorous availability on microbial carbon use efficiency and turnover rate
    Soil Biol. Biochem. (IF 5.29) Pub Date : 2020-01-08
    Bahareh Bicharanloo; Milad Bagheri Shirvan; Claudia Keitel; Feike A. Dijkstra
    更新日期:2020-01-08
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