Biocrust regulates the effects of water and temperature on soil microbial and nematode communities in a semiarid ecosystem

Global climate changes in temperature and precipitation are influencing the function of semiarid ecosystems, especially that of biocrust. Biocrust is the key biotic component in semiarid land and delivers multiple functions to belowground ecosystems. However, how biocrust affects belowground biota when temperature and water change remains unclear. We set a microcosm experiment to evaluate how soil micro-food web responds to biocrust by changing air temperature and water content. Soil microbes and nematodes were sampled at different air temperatures (10 and 25 degrees C) and soil water levels (4, 8, and 16% soil water content) under biocrust and bare soil. The results showed that biocrust highly increased soil microbe and nematode abundances compared with bare soil. Temperature change had no obvious effect on soil micro-food web. Both microbial and nematode communities were strongly affected by soil water at 10 degrees C under biocrust. Structural equation modeling analysis proved that soil pH and organic carbon were the two main factors that affected soil micro-food channels under biocrust. Soil organic carbon affected bacterial channel and fungal channel. Soil pH affected soil bacterial channel and omnivores-predators. Soil with 8% water content could provide the most stable habitat and soil environment to build a relatively complex and more reticulated soil micro-food web. It can be concluded that colonization of biocrust could buffer temperature effect on soil micro-food web. Additionally, appropriate increase in water could benefit the top-down effect between nematodes and microbes under biocrust and could contribute to the resilience of semiarid ecosystems.