Litter and microclimate controls on soil heterotrophic respiration after converting seasonal rainforests to rubber plantations in tropical China

https://doi.org/10.1016/j.agrformet.2021.108623Get rights and content

Highlights

  • Mechanisms that attributed to the soil carbon reduction after converting SR to RP.

  • Changes in soil moisture, played role in accelerating of SOC decomposition in RP.

  • Converting SR to RP can increase Q10 of Rh from the original SR SOC.

Abstract

Land-use changes can alter carbon cycling. Soil carbon loss resulting from the conversion of natural forests to rubber plantations (RP) may occur due to changes in litter inputs or in biotic and abiotic environmental conditions. In this study, we conducted a reciprocal soil and litter translocation mesocosm experiment for 15 months in a seasonal rainforest (SR) and RP to elucidate the effect of litter, soil and site conditions on heterotrophic respiration and its temperature sensitivity after land-use conversion. We found that rate of soil heterotrophic respiration (Rh) was higher at RP site than at SR site or for SR litter than RP litter with significant interactions between forest site and litter type, and did not differ between SR and RP soils. The Q10 values of Rh did not differ between forest sites, soils, or litter types but were substantially lower when litter was absent and substantially higher when RP soil was incubated in SR site and vice versa. Removal of surface litters led to a reduction of Rh by 27-45%. Soil labile organic C pool and microbial biomass were not influenced by litter type or forest site, but were influenced by soil origin, with higher values for SR soil than RP soil. Soil temperature and moisture were not influenced by litter type and soil but differed between forest sites with higher moisture at RP site than SR site. Our results suggested that changes in physical environmental conditions, rather than changes in litter input or soil biochemical properties, attributed to the elevated soil heterotrophic respiration in RP, resulting in soil carbon loss following the tropical land-use changes.

Introduction

Deforestation is known as the second largest source of the elevated atmospheric carbon dioxide. Carbon loss through deforestation and degradation of tropical forests was estimated at 0.8 Pg to 1.0 Pg C yr−1 in the last decades (Bacciniet al., 2012; Harris et al., 2012). Southeast Asia is one of the global deforestation hot spots where almost 250,000 hectares of natural forest was converted to rubber plantation (RP) between 2005 and 2010 (Ahrends et al., 2015). Rubber and other economic crops have been the major land-use changes in this region. The area of RP in Southeast Asia reached 10.4 million ha by 2017, accounting for 89% of world total RP area (FAOSTAT, 2019). Since the first rubber establishment in the 1950s, the area of RPs has increased up to 24.2% of land cover by 2014 in Xishuangbanna, Southwest of China (Chen et al., 2016).

It is recognized that soil carbon sequestration ability in RPs is much lower than that of natural forests (Jiang et al., 2017; Yang et al., 2016). This reduction in soil organic C may result from either reduced litter input or accelerated decomposition due to changed litter quality, microclimate, or soil activity. Litter production was reported to be lower in RP than in seasonal rain forest (SR) (Zhang and Zou, 2009; Zhang et al., 2013; Kotowska et al., 2016). Litter quality is lower in RP than in SR as indicated by a higher C/N ratio and aromatic carbon fractions (Zhang and Zou, 2009; Zhang et al., 2013). However, thinner floor layer in RP than SR (Zhang and Zou, 2009; Lan et al., 2020) suggests a cause of either reduced litter inputs or accelerated litter decomposition due to improved soil physical environment and soil activity, rather than litter decomposability in RP.

Soil is responsible for 60–90% of the carbon dioxide (CO2) released into the atmosphere in terrestrial ecosystems (Goulden et al., 1996). Soil CO2 efflux is the outcome of the metabolic processes of plant roots (autotrophic respiration, Ra) and microbial communities (heterotrophic respiration, Rh). The Ra refers to CO2 efflux derived from roots and the associated symbiotic organisms, Rh refers to microbial respiration of litter and root exudates as well as the transformed soil organic carbon (Sulaman et al., 2005; Kuzyakov, 2005). Because Rh could account for up to 70% of the total soil respiration (Rs) in forest stands (Sulaman et al., 2005; Fernández-Alonso et al., 2018), it is therefore important to determine how Rh responds to land-use changes from native forests to monoculture agroforestry systems (Barba et al., 2016; Fernández-Alonso et al., 2018).

The conversion of native forest to monoculture RP may result in changes in plant litter input, soil biochemical properties such as microbial biomass and soil labile organic carbon, or in environmental conditions that include microclimate and soil water content (Liu et al., 2011, Meijide et al., 2018; Song et al., 2017; Lan et al., 2020), and consequently alter soil respiration and soil carbon stock. Temperature is the essential factor controlling soil metabolic activities; thus, the kinetics of CO2 efflux had been modeled by various temperature-dependent functions. Many hypotheses were postulated to link the response of Rh to soil temperature (Tuomi et al., 2008; Tremblay et al., 2018; Salazar et al., 2019). However, the temporal variability of Rh observed in field experiments captures not only its dependence on soil temperature, but also reflects the influence on decomposition caused by seasonal changes in substrate quality and quantity, soil moisture and soil community (Gonzalez et al., 2001; Hou et al., 2005; Fernández-Alonso et al., 2018; Huang et al., 2020), as well as their interactions (Wall et al., 2008). Strong variations in seasonality of modeled soil Rh was commonly observed, suggesting an apparent limitation to soil metabolic activity beyond that could be explained by temperature. Furthermore, homeostasis of native soil microbial community would suggest Rh dependency on soil organisms, which were also greatly constrained by soil water and temperature (Fernández-Alonso et al., 2018).

We conducted this study to elucidate the influence of aboveground litter input, forest soils and its organisms, and forest microclimate and water content on soil Rh and its temperature sensitivity following conversion of natural forest to RPs. A 15-month reciprocal soil and litter translocation mesocosm experiment were performed in Xishuangbanna of SW China. In the root-exclusion treatment it was assumed that Ra was completely suppressed and hence solely Rh occurred that the CO2 efflux derived from the microbial decomposition of soil organic matter and litter. We collected in-situ data on soil Rh, litterfall, soil labile organic carbon, soil microbial biomass, and soil temperature and moisture from these mesocosms in SR and RP. We hypothesized that reduction of TOC in RPs was resulted from (1) reduced production of above-ground rubber litter, or (2) accelerated soil heterotrophic respiration and altered temperature sensitivity of TOC due to improved physical environmental conditions such as temperature and moisture or soil biochemical properties such as microbial biomass and soil labile organic carbon.

Section snippets

Site description

Study sites were located in the Xishuangbanna Tropical Botanical Garden (XTBG, 21°54′N, 101°46′E), near the monitoring plots of the Chinese Ecological Research Network supported by the Chinese Academy of Sciences. The annual mean temperature in the region is 21.8°C and the annual mean precipitation is 1493 mm (Cao et al., 2006). This region is strongly influenced by the tropical monsoons that bring warm and humid air from the northeastern Indian Ocean during the months of May through October.

Controls on heterotrophic respiration

Soil respiration rates varied greatly, ranging from 1.8 µmol m−2 s−1 to 14.3 µmol m−2 s−1 at the SR site and from 3.6 to 28.1 µmol m−2 s−1 at the RP site. Soil respiration rate without litters was on average about 68% of that with litters. Annual Rh was apparently greater in RP than SR sites, and in treatment with litter than without litter inputs, suggesting that physical environment and the presence of litter had significant influences on annual Rh (Fig. 1). The average Rh of soils incubated

Discussion

Reduction in TOC following conversion from SR to RP may have resulted from one or more of these factors: improved physical environment for decomposition, improved quality of organic C for decomposition, reduced litter input, and increased biotic activity in decomposition. In this study, soil Rh in RP site was overall higher than that in SR site, whereas aboveground litter input and soil origin had no significant influences on Rh. Higher C/N ratio (Zhang et al., 2013) of RP litter (42.5±1.0)

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was financially supported by the Asia-Pacific Network for Global Change Research (ARCP2008-19NMY).

References (45)

  • X Yang et al.

    Land use change impact on time-averaged carbon balances: rubber expansion and reforestation in a biosphere reserve, South-West China

    Forest Ecology and Management

    (2016)
  • M Zhang et al.

    Decomposition differences of labile carbon from litter to soil in a tropical rain forestrainforest and rubber plantation of Xishuangbanna

    European Journal of Soil Biology

    (2013)
  • M Zhang et al.

    Alteration of soil labile organic carbon by invasive earthworms (Pontoscolex corethrurus) in tropical rubber plantations

    European Journal of Soil Biology

    (2010)
  • X Zhu et al.

    Effects of land-use changes on runoff and sediment yield: implications for soil conservation and forest management in Xishuangbanna

    SW china. Land Degradation and Development

    (2018)
  • X Zou et al.

    Estimating soil labile organic carbon and potential turnover rates using a sequential fumigation incubation procedure

    Soil Biological and Biochemistry

    (2005)
  • A Baccini et al.

    Estimated carbon dioxide emissions from tropical deforestation improved by carbon-density maps

    Nature Climate Change

    (2012)
  • Z Bai et al.

    Shifts in microbial trophic strategy explain different temperature sensitivity of CO2 flux under constant and diurnally varying temperature regimes

    FEMS Microbiology Ecology

    (2017)
  • J. Barba et al.

    Strong resilience of soil respiration components to drought-induced die-off resulting in forest secondary succession

    Oecologia

    (2016)
  • M Cao et al.

    Tree species composition of a seasonal rain forest in Xishuangbanna, Southwest China

    Tropical Ecology

    (1996)
  • M Cao et al.

    Tropical forests of Xishuangbanna, China

    Biotropica

    (2006)
  • H Chen et al.

    Pushing the limits: the pattern and dynamics of rubber monoculture expansion in Xishuangbanna, SW China

    PLoS One

    (2016)
  • Food and agriculture data

    Crops

    (2019)
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