Macropores created by invertebrates improve ecosystem functions such as soil properties and hydrological processes. In semi-arid savannas, where water is the main limiting resource and precipitation is scarce macropores might increase infiltration, and thereby improve water availability for plants. Macropores may therefore represent a buffering mechanism counteracting degradation in the form of shrub-encroachment. We investigated the interacting effects of vegetation structures at small scales and vegetation cover at landscape scales, and seasonality on invertebrate macropores. First, macropore density and size distribution was measured at open soil, in direct proximity to perennial grass tussocks and shrubs, at grass dominated, intermediate and shrub dominated sites. Secondly, we recorded macropores on randomly chosen plots along a shrub cover gradient at three points in time within the rainy season. Individual shrubs and the amount of large scale grass cover increased macropore densities. Interestingly, macropore numbers were highest at the beginning of the rainy season. We argue that macropore densities reflect the activity and influence of soil macrofauna on ecosystem functioning, which is greatest at highly heterogeneous vegetation. Rangeland management should aim for high grass cover with scattered shrubs for sustainable soil health, by applying appropriate stocking rates, selectively removing shrubs or reseeding perennial grasses.

Biocrusts presented their highest expression in the inter-patches. However, an increase in the level of aridity along the landscape could lead to vascular plants to make a notable influence on the spatial distribution of biocrusts. Our objective was to determine the spatial variation of the vascular plant interactions with biocrusts, and the individual variations of biocrusts and each of its components along a gradient of aridity in Argentina. We worked on three sites following a semiarid-arid-hyperarid environmental aridity gradient. We established 15 plots along the stress gradient. In each plot, we evaluated the spatial distribution of cyanobacteria, mosses, and lichens and the interaction with the dominant shrubs using a distance index analysis. The hyperarid site showed an aggregate distribution pattern for each biological group (biocrusts, mosses, lichens, and cyanobacteria). The semiarid site showed an aggregate distribution for mosses and cyanobacteria. Respect to the interaction with the shrubs, only the hyperarid site showed a positive interaction between shrubs and the components of biocrusts. We found positive interactions of lichens on the semiarid site, but the arid studied site did not show interactions. Reductions in vegetation cover could directly influence in the biocrust coverage, generating impacts on ecosystems.

Soil microbial communities, which play important roles in biogeochemical cycling, are affected by plants in many ways. To understand how plants affect soil microbes, we compared soils under halophytic shrubs and herbs, whose effects on soil salinity (one of the strongest determining factors for soil microbes in saline grasslands) were different. We measured soil physicochemical properties, as well as prokaryotic abundance, community structure, diversity, and the quantified and predicted abundances of functional genes for nitrogen (N) cycling. As we intended, we found the soil salinity to be the highest in barren areas (BA), intermediate under a tamarisk crown (UC), and the lowest in herbaceous patches (HP), whereas other plant-related properties, e.g. soil organic matter content, differed between vegetated areas (UC and HP) and BA. Prokaryotic community structure and diversity changed along the soil salinity gradient, but not as a function of plant presence or absence. However, N transformation rate and N availability were not affected by the salinity gradient alone. The dominant prokaryotic groups that contributed the most to changes in prokaryotic community structure and diversity were likely not those primarily responsible for N mineralization.

In arid and semi-arid regions, unregulated land use changes as a result of poor planning, and the expansion of agricultural and livestock activities increase the risk of desertification and other potentially severe environmental impacts. Several consequences of improper land management practices are soil deterioration and erosion, which may be intensified by meteorological events. This paper presents a historical evaluation of the temporal and spatial evolution of soil deterioration in the southern Chihuahuan Desert in Mexico. A multi-temporal analysis of the study area during the 1995–2016 period was carried out using satellite data (Landsat series). Two seasons were analyzed to determine the influence of external events such as rainfall and wind: dry and rainy. The identification of soil conditions was based on the Brightness Index (BI) considering the complete satellite data set. The soil conditions were classified into five categories according to their reflectance values: highly deteriorated, deteriorated, in the process of being deteriorated, in good condition and other (clouds, water, non-soil). The change detection maps clearly show a growing trend wherein areas of deteriorated and eroded soil increase over time. Agriculture and strong winds are the two main factors involved in the soil deterioration process of the study region.

The term South American Arid Diagonal (SAAD) has been, and still is, widely used by the scientific community working in South America's drylands. The present research relies on the assumption that such usage is made in a superficial manner, the SAAD being solely a locational reference which is systematically used by specialists in diverse disciplines to spatially circumscribe their work, but without enriching it with new contents or pondering all of its scopes. Bearing this in mind, we sought to dig deeper into the analysis of the origin and evolution of the SAAD's concept in relation to scientific knowledge, and also give an account of its current use. To this end, we conducted a thorough review and systematic analysis of literature sources mentioning the SAAD, both those available in Internet search engines and in non-indexed documents. This was used as a basis to conduct a bibliometric and network analysis of 88 indexed publications. From the main results, it can be seen that most authors use the concept only as a spatial reference for their study sites, on many occasions using wrong quotes, frequently referring to “quotes of quotes”, ignoring the geographic extent of the concept and evidencing that, except for those of the founding authors, later contributions were not significant for gaining knowledge of the SAAD. The qualitative approach to non-indexed sources also allowed clearly identifying the authors who defined the concept, whose close connection with geographic science stands out noticeably. A correlation between the stages of evolution of geographic thought and the times at which contributions are made to the SAAD is evidence of the fundamental imprint of French Regional Geography. Despite its successive crises, booms and busts, the influence of this current on the definition of SAAD remains in force, and has remained so for over seventy years.

Drought-induced mortality has been reported in many forest biomes around the world. In recent years, large-scale forest mortality has been observed across northern China, with forests exhibiting widespread crown dieback symptoms. Previous reports have attributed dieback and mortality to drought stress. In this study, a field survey was undertaken along two transects in northern China. Our aims were to clarify the underlying mechanisms of the widespread dieback and mortality of poplar (Populus spp.) plantations under various environmental stresses. Under these conditions, we observed narrower tree-ring width, and decreased soil water content, indicating that forest growth increased drought stress, and drought stress played a prominent role in triggering dieback and mortality. Bacterial canker disease and low soil nutrient were also linked to dieback and mortality. We observed xylem damage, showing that latent bacterial canker disease was present in many poplar tree stands across northern China, which may increase their susceptibility to drought stress. The results showed that widespread dieback and mortality of poplar forests were related to the interaction of drought stress, bacterial canker and low soil nutrient. The results contributed to understanding the causes for poplar plantation deaths, and could help in the prevention of large-scale death of poplar plantations.

Plant checklists constitute the fundamental knowledge on which further hypotheses of ecology, evolution, and biodiversity conservation are built. Here, we compiled a comprehensive and taxonomically verified checklist of the flowering plant species occurring in the Caatinga. We circumscribe Caatinga to include only the dry deciduous vegetation in Northeast Brazil, corresponding to the largest continuous nucleus of the seasonally dry tropical forest and woodland biome (SDTFW) in South America. We recorded 3347 species, 962 genera, and 153 families, of which 526 species and 29 genera are endemic, and the large contribution of its non-woody component to overall diversity. These numbers reveal a remarkably high floristic diversity in the Caatinga, representing almost two fold higher species/area ratio (4.0 × 10−3 species/km2) as compared to the Amazon rainforests (2.5 × 10−3 species/km2). Most Caatinga-inhabiting species are shared with other non-SDTFW tropical biomes, probably reflecting transition zones with surrounding savannas and rain forests. This newly assembled taxonomic checklist is expected to serve not only as an updated look at the identity and counting of the Caatinga plant diversity, but will also provide aids for better understanding the origin, evolution, and ecological function of this species-rich, but highly threatened South American vegetation.

Species richness has become the common currency of studies of biodiversity. Here we consider measures of species richness for the birds of the arid Karoo region of South Africa. We measured species richness at two scales: at the broad-scale using pentads (5 × 5′); and at the fine scale, using point counts to determine important landscape features. Point counts within randomly selected pentads were conducted throughout the two biomes that comprise the Karoo (Succulent and Nama). Features at points were used to model covariates of species richness at the fine scale, while the total number of unique species from counts was used as the dependent variable at the broad scale. We considered determinants of total species richness; and the subset of ten bird species endemic to the Karoo. Finally, we modelled covariates of presence for 100 of the most common bird species. We found increasing vegetation height and decreasing sand-cover best explain total species richness, while lower Prosopis sp cover and increasing altitude explained endemic species richness at the broad scale. At the finer scale, presence of water and farmsteads were associated with highest general species richness, but with lower numbers of endemics. The presence of water, a ‘green’ score, sand cover and topography were identified as the most important variables explaining presence of individual species, but often with contrasting effects between species. We conclude that patterns of endemic bird species richness were explained by different variables compared to total species richness. We expect this information will inform landholders, wildlife managers and conservation practitioners in this unique arid zone environment.

Management of environmental resources presents challenges across agricultural production. In the case of the semi-arid region of Arava Valley in Israel irrigation with groundwater brackish water is a widespread practice that has severe limitations. In this research studies are taking place for brackish groundwater upgrading for unrestricted use for irrigation and sustainable agricultural production. The treatment system applies two main treatment stages: nanofiltration and reverse osmosis membrane process and, the pilot system with the capacity of around 1 m3/h. Different mixtures of nanofiltration and reverse osmosis, Brackish and potable permeates are then applied for irrigation of pepper crops. The field results together with the graphical visualization approach using Hasse diagram technique show that the conventional brackish feed water produces good revenue about fruit weight, fruit diameter, and fruit length. A membrane treatment using nanofiltration and reverse osmosis yields an increase in production (more fruit number). Extension of the research at the field level may aid to optimize irrigation use strategy to increase the food production.

The pollination systems of columnar cacti in the dry tropics are often thought to be highly specialized to bats. This specialization is generally inferred when flowers that are only exposed to the activity of nocturnal visitors set fruit and seed. Although moths are also common visitors to the flowers of columnar cacti at night, it is generally thought that their contribution to the reproductive success of this cactus is negligible. Using selective exclusions, we assessed the contribution of bats and moths to the reproductive success in a population of Pilosocereus leucocephalus in central Mexico. Fruit set was 100% for bat-pollinated flowers and 34% in moth-pollinated flowers. Seed number per fruit was 1473 in bat-pollinated and 836 in moth pollinated flowers. Our results clearly show that in addition to bats, moths are effective pollinators of Pilosocereus leucocephalus in the study area. Therefore, bats are the main pollinators of P. leucocephalus, and moths are the secondary pollinators.

We recorded video providing the first conclusive evidence that the black-tailed jackrabbit (Lepus californicus) consumes Mojave milkweed (Asclepias nyctaginifolia) containing phytochemicals in the Ivanpah Valley, Mojave Desert, California, USA. We discuss possible chemical and biological interactions between the black-tailed jackrabbit and Mojave milkweed. We explore potential ecological effects of black-tailed jackrabbit herbivory on Mojave milkweed, including competition with the monarch butterfly (Danaus plexippus) and its close relative the queen butterfly (Danaus gilippus), and how these ecological interactions may be affected by anthropogenic land-use and land-cover change in arid environments of the western United States.

Vivipary implies that seeds germinate inside the fruit still attached to the mother plant. Vivipary may constitute an adaptive trait, which may allow the quick establishment of seedlings in harsh environments. The Bromeliaceae includes ca. 3,140 species in many ecosystems, but vivipary appears to be infrequent in bromeliad epiphytes. In this research, we studied the vivipary incidence in Tillandsia recurvata from the Southern Chihuahuan Desert, during two years. We collected one fruit from each of five T. recurvata individuals, in ten Prosopis laevigata trees (50 fruits in total) inside 1 ha. These trees were at least 10 m apart. Fruit collection was conducted on September 7, 2016, and August 20, 2017, after fruit ripening and during the rainy season. Collected fruits were cleaned and opened to quantify the number of viviparous seedlings within each of them during 2016 and 2017. Vivipary incidence (%) in the collected fruits was not statistically analyzed because we found 100% of viviparous seedlings in both collection years. There were on average 69.59 and 71.44 seedlings per fruit per individual in 2016 and 2017, respectively. We attached groups of seedlings (all seedlings from each fruit) together, to mesquite branches and monitored seedling survival every two weeks for one year. At least one seedling lived from 66% of the fruits after 1 yr. Complete vivipary incidence in T. recurvata is probably adaptive because roots of seedlings may attach to hosts more readily than seeds without roots.

Desertification is a dynamic and complex system of land degradation. To understand it, physical and anthropogenic processes and their interrelations need to be identified. This study aimed to provide early warning information on desertification risk in the form of warning maps, using effective key indicators of land degradation in a 15-year period in the arid regions of northeastern Iran. E-SMART key Indicators should be E: Economic, S: Specific, M: Measurable, A: Achievable, R: Relevant, and T: Time-bound. Multiple regression analysis showed that the majority of indicators could accurately assess desertification risk at a 99% confidence level with R2 = 0.81. Furthermore, compared to the beginning of the study period, areas under desertification warning due to natural and anthropogenic factors had increased by about 78 percent in 2015. This observation is aligned with the impacts of drought, which has resulted from the continued reduction in rainfall. The expansion of at-risk areas has in turn exacerbated the adverse environmental conditions and amplified the effects of drought in the area. Spatio-temporal changes in soil salinity, groundwater quality, groundwater level, vegetation, agricultural development, and socioeconomic issues showed that the study area has suffered from land degradation and desertification between 2000 and 2015.

Decentralised energy from feedstock cultivated on marginal land can address various problems of many developing countries. Plants like Opuntia ficus-indica (L) Mill. (Cactaceae) and Euphorbia tirucalli L. (Euphorbiaceae) are adapted to thrive on marginal land and hence ideal for feedstock production without competing for arable land. This study explored the potential of intensive cultivation of these plants under various planting densities on marginal land blocks, each having an area of 900 m2, and compared the specific methane production potential of their biomass. Biomass samples from the wild mother plants and those from the cultivated blocks were analysed for their elemental and plant composition. The Hohenheim Biogas Test (HBT) was employed to test their biogas/methane yield potential of the biomass samples. The study showed that high density planting did not negatively affect the plant growth and biomass production. During four month growth time, the plantations at highest density (Euphorbia tirucalli at 266667 plants/ha and Opuntia ficus-indica (L) Mill. at 20.000 plants/ha) were able to generate a methane yield of approximately 1791 m³ in the case of Euphorbia tirucalli L. and 1860 m³ in the case of Opuntia ficus-indica (L) Mill. from 1 ha of marginal land.

Water supply and distribution are the main limiting factors to wheat (Triticum aestivum) yield in a semi-arid region of the U.S. southern Great Plains. To manage crop water demand, limited irrigation (also called deficit irrigation) is commonly practiced in the region. A 4-yr study was conducted to evaluate yield in winter wheat cultivars as influenced by the depth and amount of net soil water extraction (SWE) under limited irrigation. For timing the irrigation application, we considered critical growth stages (jointing, tillering, and anthesis) as well as soil water depletion at the crop root zone below 50%. Volumetric soil water content was measured in 0.2 m increments to the depth of 2.4 m at planting, jointing, anthesis, and physiological maturity. Since the irrigation capacity was limited, seasonal precipitation was still an important factor for determining SWE. The 2011 season was one of the historic drought seasons with only 60 mm of seasonal precipitation and the net SWE in that season was limited to the upper 1.2 m profile. In contrast, the 2016 season was more favorable for crop growth with 315 mm of seasonal precipitation and the net SWE in that season reached to 2.0 m deep. Grain yield was largely influenced by the amount of net SWE during the growing season. For the wheat with grain yield of 4807 kg ha−1, net SWE was 165 mm (2016). However, wheat with grain yield of 2933 kg ha−1 only extracted 70 mm stored soil water (2011). The 2012 and 2017 seasons remained intermediate in terms of seasonal precipitation, SWE, and yield. Although the 2011 and 2016 seasons had similar stored soil moisture at planting, more early-season as well as total precipitation in 2016 appears to have enabled plant growth to access the deeper water. In contrast, a greater amount of stored soil water was left unused at the end of the 2011 season due to drought and poor plant growth. Hence, in addition to adding water at critical growth stages, ensuring early plant growth to promote root development for extracting soil water from the deeper profile later in the season should be a key strategy to take full advantage of limited irrigation.

According to the social changes in the 1990s, livestock population in Mongolia is rapidly increasing, resulting in overgrazing and subsequent degradation of the grasslands. However, little is known about the quantitative food habits of Mongolian livestock. We evaluated the food habits of horses, cattle, and sheep and goats in the forest–steppe zone of northern Mongolia by fecal analysis. We compared fecal compositions at a valley (Place 1) and a riverside (Place 2). Place 1 consisted mainly of Stipa-dominated slopes (93%) while Place 2 comprised Stipa-dominated slopes (77%) and Carex-dominated alluvial flats (23%). Horse feces were dominated by graminoids (60%–70% graminoids), with a high percentage of Carex (30%–40%). Stipa accounted for about 20%–40% in the cattle feces. Sheep and goat feces contained about 30% Stipa and about 40% culms. These results suggest that the food habits of the livestock were affected more by animal characteristics than habitats. The high Carex content in the horse feces occurred because horses roamed freely and could visit Carex swards. Cattle moved near the gers (tent houses) and returned every evening, and it was difficult for them to visit far away Carex swards. Sheep-goats were herded and often grazed on steeper slopes than cattle and horses, explaining the large proportion of culms and small proportion of Carex in the feces. Quantitative food habit studies of livestock is useful for the grassland management of arid regions.

This study explored the process of pastoral livelihood transition and driving factors from 1987 to 2017 in northern Xinjiang and analyzed the internal determinants of grazing and nonfarm participation in 2017. Based on the classification tree method, livelihood strategies were classified into six types. The livelihood change rate accelerated over time, and livelihoods displayed different characteristics over the three decades: pastoralist livelihood with high mobility, mixed agro-pastoral livelihood with reduced mobility, and diversified livelihood around settlements. The transition occurred principally because of the increased support of the pastoralist sedentarization policy and the development of irrigation agriculture and secondary and tertiary industries. Contemporarily, households with rich natural capital and livestock tended to adopt grazing; a lack of these assets and higher level of Mandarin proficiency enhance the propensity for nonfarm participation. Future pastoral policy should emphasize the synergistic development of agriculture and non-agriculture to facilitate livelihood diversification.

Climatic change will seriously impact Mediterranean areas. Palestine, which has given forth annual grain based agriculture, is particularly vulnerable given its political and economic situation. Research is needed to build climate adaptation and resilience into agroecosystems within the same landscape that gave forth agriculture. A primary step in achieving that adaptation is to develop polycultures composed of perennial crops to protect and rebuild the soil. Our preliminary research shows that agrobiodiversity and genetic material for this deep adaptation is already present within the landscape, and if developed could produce the new crops used to build perennial polycultures.

Woody vegetation provides multiple services to the pastoralists in the Sahel and since the drought of 1972–1984, concerns have been raised about its persistence. Some studies have observed a decline in tree density and specific richness while others have reported a greening at a larger scale. In this study, an extensive field inventory was carried out around two deep wells in the Ferlo (Senegal). The influence of topography and proximity of deep wells on woody vegetation density, diversity and regeneration was studied. An analysis of the size class distribution was carried out to gain insight into the population dynamics of some species. This study highlights the key role of low topographic positions in favouring woody vegetation establishment with a higher species richness and a greater density. The remoteness of deep wells seems to have no effect on these variables. The instability of several tree species populations was evident from the size class analysis. As large trees play an important role in hosting regeneration, the persistence of the current woody vegetation is threatened. Given the positive impact of depressions on woody vegetation, further research should focus on these topographic features and their role as central pieces in a potential management plan.

Debris piles and dry pools are common landscape elements along ephemeral river channels. However, their effects on resource availability and arthropod species diversity have been neglected so far. We investigated whether debris piles and pools along dry riverbeds generate nodes of environmental resources, influence microbial activity, and provide key habitats for ground-dwelling arthropods. We studied three different habitats (channel, debris pile and dry pool) to analyze organic matter, nutrients and microbial activity in dry sediments, and included two further habitats (riparian and upland areas) for ground-dwelling arthropod assemblages along a major ephemeral river (Ugab River, NW Namibia). We observed higher concentrations of organic matter and macro- and micro-nutrients in debris piles than in pools, and higher concentrations in both landscape elements than in the sandy channel matrix. Microbial activity showed a positive relationship with organic matter and nutrient availability in sediments. Debris piles, dry pools and channels harbored diverse and abundant ground-dwelling arthropod assemblages similar to adjacent terrestrial areas. Debris piles and pools differed in assemblage composition not only from riparian and upland areas but also from the sandy channel matrix. Overall, debris piles and dry pools acted as nodes of soil fertility, enhanced microbial activity, and shaped ground-dwelling arthropod assemblages.

Climate change will likely impact rainfall characteristics in particular locations; the amount, seasonality, variability and spatial patterns. In developing countries, this presents challenges for rural smallholder farmers as their livelihoods are largely based on rain-fed practices. Changes in climate patterns could increase farmers' vulnerability and the need for intervention. In this paper, we develop new metrics of analysis motivated by qualitative research with smallholder farmers. Previous research found that farmers' understanding of historical rainfall change is accurate, yet diverge from some research studies. We analyze meteorological station rainfall data using metrics that are familiar to smallholders. Farmers' perceptions of rainfall in southern Ethiopia were explored through interviews conducted in three communities. Our findings identified some forms of convergence, as well as divergence, in farmers' perception of rainfall trends and meteorological station data results. In asking the question ‘Why do data based on farmer experiences of rainfall variability differ from meteorological station data?’, we show that using existing data and applying farmer-influenced metrics can improve the information shared with farmers. We argue that, under further climate change, it will be increasingly important to convey meteorological information to farmers in ways that are relevant to them and their agricultural livelihoods.

Facilitation may contribute to conserving natural systems disturbed by humans. We hypothesized that the unpalatable native weed, Baccharis ulicina (Baccharis) protects palatable plants from cattle grazing in central Argentina grasslands. We tested this hypothesis through observational and experimental studies. In the observational study, we compared consumption and performance of plants growing in Baccharis and Baccharis-free (open) microsites. We also recorded photosynthetically active radiation, soil moisture, and total soil nitrogen (N) in both microsites. In the experiment, we removed Baccharis aboveground biomass and compared herbivory and plant performance in Baccharis, Baccharis-removed, and open microsites. Palatable plants were less consumed when growing with than without Baccharis, and palatable grasses with the highest forage values were more abundant, taller, and fecund in Baccharis than open microsites in our observational study. Additionally, except for increased radiation in the open, there were no differences in abiotic variables between microsites. Results from the plant removal experiment were consistent with those from the observational study and did not offer evidence for direct facilitation. We conclude that protection from cattle is an important mechanism through which Baccharis benefits neighboring plants. Our work emphasizes the need to recognize the facilitative role of weeds in the management of semi-arid grasslands.

Monitoring ecosystem functioning is a significant step towards detecting changes in ecosystem attributes that could be linked to land degradation and desertification in drylands worldwide. Remote sensing-based vegetation indices (VIs) and land surface albedo are two favorite indicators to monitor desertification process due to their close relationship with ecosystem status and to their increasing applicability over multiple spatiotemporal scales. While VIs are routinely used to monitor ecosystem attributes and functions such as vegetation cover and productivity, no previous study has evaluated whether remote sensing-measured albedo is related to the simultaneous provision of multiple ecosystem functions (multifunctionality) in global drylands. In this study, we evaluated the correlation of six albedo metrics (shortwave black-sky albedo, shortwave white-sky albedo, visible black-sky albedo, visible white-sky albedo, near-infrared black-sky albedo and near-infrared white-sky albedo) and two VIs (Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI)) with multifunctionality indices related to carbon, nitrogen and phosphorus cycling measured in 61 dryland ecosystems from all continents except Antarctica. We found a negative relationship between land surface albedo and multifunctionality. Black-sky albedo had a stronger correlation with multifunctionality than white-sky albedo. Visible black-sky albedo showed the strongest correlation with multifunctionality (MUL, -0.314), as well as with functions related to carbon (CCY, -0.216) and nitrogen cycling (NCY, -0.410), while near-infrared (-0.339) and shortwave black-sky albedo (-0.325) showed stronger correlations with functions related to phosphorus cycling (PCY) than visible black-sky albedo (-0.233) did. VIs showed significant positive correlations with MUL, CCY, and NCY, and the magnitudes were higher than those observed between albedo metrics and the multifunctionality indices. However, VIs were not correlated with PCY, which had significant correlations with both shortwave and near-infrared albedo. Though the magnitudes of the correlations observed were not high, which may result from the wide variability in soil and vegetation types in our dataset, our findings indicate that remotely sensed albedo correlates to multifunctionality, which has been linked to alternative states in global drylands. As such, albedo has the potential to monitor changes in dryland ecosystem functioning, which can inform us about the onset of desertification in these areas.

We evaluated the net outcome of the interaction between the shrub Retama sphaerocarpa, our target plant, and different herbaceous neighbours in response to changes in the magnitude and frequency of rainfall events during three years. The experiment was conducted in natural and anthropogenic grasslands dominated by a perennial stress-tolerator and ruderal annual species, respectively. In spite of the neutral or positive effects of neighbours on water availability, neighbouring plants reduced the performance of Retama juveniles, suggesting competition for resources other than water. The negative effects of grasses on the photochemical efficiency of Retama juveniles decreased with higher water availabilities or heavier irrigation pulses, depending on the grassland studied; however, these effects did not extent to the survival and growth of Retama juveniles. Our findings show the prevalence of competitive interactions among the studied plants, regardless of the water availability and its temporal pattern. These results suggest that positive interactions may not prevail under harsher conditions when shade-intolerant species are involved. This study could be used to further refine our predictions of how plant-plant interactions will respond to changes in rainfall, either natural or increased by the ongoing climatic change, in ecosystems where grass-shrubs interactions are prevalent.

High levels of atmospheric nitrogen (N) deposition to southern California chaparral shrublands may interact with fire to affect biomass production and plant species composition during secondary succession. To determine the potential interactions between post fire recovery and N deposition we compared rates of aboveground net primary production (ANPP), shrub growth, and the relative abundance of Adenostoma fasciculatum, other sub-dominant shrubs, and herbaceous species of three chaparral stands exposed to different levels of atmospheric N deposition over the first 3 years of post-fire succession. Our data suggest that rates of ANPP (gdw m(-2) month(-1)) and aboveground N storage (gN m(-2) month(-1)) for these chaparral stands were not related to N deposition even though sites exposed to high levels of N deposition had significantly higher rates of shrub growth (gdw plant(-1) month(-1)) and N uptake (gN plant(-1) month(-1)). However, high-N stands were composed of larger shrubs with a lower density, and this trade-off between shrub size and density may explain the low correlation between N deposition and post-fire ANPP. Differences in relative plant species abundance between sites were significantly correlated with N deposition exposure, where stands exposed to high N deposition had a lower relative abundance of A. fasciculatum and a higher relative abundance of other shrub and herbaceous species. While many factors can affect rates and patterns of post-fire recovery, these results suggest that chronic exposure to N deposition may significantly alter plant growth and species composition in successional chaparral stands.

The effects of elevated atmospheric carbon dioxide [CO(2)] on microbial communities in arid rhizosphere soils beneath Larrea tridentata were examined. Roots of Larrea were harvested from plots fumigated with elevated or ambient levels of [CO(2)] using Free-Air CO(2) Enrichment (FACE) technology. Twelve bacterial and fungal rRNA gene libraries were constructed, sequenced and categorized into operational taxonomical units (OTUs). There was a significant decrease in OTUs within the Firmicutes (bacteria) in elevated [CO(2)], and increase in Basiomycota (fungi) in rhizosphere soils of plots exposed to ambient [CO(2)]. Phylogenetic analyses indicated that OTUs belonged to a wide range of bacterial and fungal taxa. To further study changes in bacterial communities, Quantitative Polymerase Chain Reaction (QPCR) was used to quantify populations of bacteria in rhizosphere soil. The concentration of total bacteria 16S rDNA was similar in conditions of enriched and ambient [CO(2)]. However, QPCR of Gram-positive microorganisms showed a 43% decrease in the population in elevated [CO(2)]. The decrease in representation of Gram positives and the similar values for total bacterial DNA suggest that the representation of other bacterial taxa was promoted by elevated [CO(2)]. These results indicate that elevated [CO(2)] changes structure and representation of microorganisms associated with roots of desert plants.

Semi-arid shrublands of southern California, including chaparral and coastal sage, are found in widely varying elevation and microclimatic regimes and are subjected to disturbance such as fire and atmospheric N deposition that have the capacity to alter soil and litter C and N storage. Here we present a case study where soil and litter C and N were measured over 19 months in post-fire chaparral and mature coastal sage stands to assess whether differences in soil and litter C and N between these diverse shrublands could be attributed to differences in elevation, stand age, rainfall, and/or estimated N deposition exposure. Our results indicate that atmospheric N deposition exposure, either alone or in conjunction with other environmental variables (elevation, rainfall, and/or stand age), was the most frequent predictor of the spatial pattern in the soil and litter N and C variables observed. These results are consistent with those reported for high-elevation coniferous forests arrayed along an N deposition gradient in southern California, suggesting that N deposition may affect the soil N and C storage of semiarid shrublands and woodlands in a qualitatively similar manner.

Microbial populations within hypersaline lakes often exhibit high activities of photosynthesis, dissimilatory sulphate reduction and other processes and, thus, can have profound impacts on biogeochemical cycles of carbon, nitrogen, sulphur and other important elements within arid lands. To further understand these types of ecosystems, the physicochemical and biological properties of Sidi Ameur and Himalatt Salt Lakes in the Algerian Sahara were examined and compared. Both lakes were relatively neutral in pH (7.2 to 7.4) and high in salt, at 12% and 20 % (w/v) salinity for Himalatt and Sidi Ameur Lakes, respectively, with dominant ions of sodium and chloride. The community compositions of microbes from all three domains (Bacteria, Archaea and Eukarya) were surveyed through the use of 16S and 18S ribosomal gene amplification and clone library clustering using amplified ribosomal DNA restriction analysis (ARDRA) in conjunction with DNA sequencing and analysis. A high level of microbial diversity, particularly among the bacteria of the Himalatt Salt Lake and archaea of Sidi Ameur Lake, was found within these environments. Representatives from all known halophilic bacterial phyla as well as 6 different genera of halophilic archaea were identified. Moreover, several apparently novel phylotypes among both archaea and bacteria were revealed.

Desert springs are critical for wildlife and human subsistence, but poorly studied. The springs in the northern Chihuahuan Desert region of Mexico are no exception. While groundwater overexploitation and other anthropogenic activities have endangered these waters, little is known about their water quality or biodiversity. We monitored five springs on a monthly basis for one year, and two others sporadically, to determine their physicochemical characteristics and to study rotifer community composition as an assessment of biodiversity. Seasonal variation in temperature, dissolved oxygen (DO), and conductivity was observed in the five springs. DO was occasionally below the criterion for aquatic life (<4mg/L) in some springs. Ca2+ (468-775.2 mg/L) was the dominant ion in all springs except Ojo de Santa María where Na+ (180-290 mg/L) dominated. Of 57 rotifer species identified, Lepadella patella (Müller, 1786), Lepadella triptera (Ehrenberg, 1830), and Philodina megalotrocha, Ehrenberg, 1832 were present in most springs. The rotifer community exhibited nestedness among the sites (supported by four null modes, p<0.05) and was correlated with fall season, DO, and nitrate concentration. This work provides information that will aid in management practices and provide important baseline data on water quality and regional diversity of a major component of the zooplankton.

Cyanobacteria are a key constituent of biocrusts, communities dominated by lichens, mosses and associated microorganisms, which are prevalent in drylands worldwide and that largely determine their functioning. Despite their importance, there are large gaps in our knowledge of the composition and diversity of cyanobacteria associated with biocrusts, particularly in areas such as the Mediterranean Basin. We studied the diversity of these cyanobacteria in a gypsiferous grassland from Central Spain using both morphological identification after cultivation and genetic analyses with the 16S rRNA gene. Nine different morphotypes were observed, eight corresponding to filamentous, and one to unicellular cyanobacteria. We found cyanobacterial genera typical of biocrust communities, such as Microcoleus and Trichocoleus, and N-fixing cyanobacteria such as Scytonema and Nostoc. Genetic information allowed us to identify cultures belonging to recently described genera such as Roholtiella, Nodosilinea and Mojavia. We also describe two new phylotypes of Microcoleus and Scytonema, which are key genera contributing to ecosystem functioning in biocrust-dominated ecosystems worldwide.

Biological soil crusts (BSCs), composed of lichens, cyanobacteria, mosses, liverworts and microorganisms, are key biotic components of arid and semi-arid ecosystems worldwide. Despite they are widespread in Spain, these organisms have been historically understudied in this country. This trend is beginning to change as a recent wave of research has been identifying BSCs as a model ecological system. Many studies and research projects carried out in Spain have explored the role of BSCs on water, carbon and nitrogen fluxes, the interactions between BSCs and vascular plants, their dynamics after disturbances, and their response to global change, among other topics. In this article we review the growing body of research on BSCs available from semi-arid areas of Spain, highlighting its importance for increasing our knowledge on this group of organisms. We also discuss how it is breaking new ground in emerging research areas on the ecology of BSCs, and how it can be use to guide management and restoration efforts. Finally, we provide directions for future research on the ecology of BSCs in Spain and abroad.