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

Abstract

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°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°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.

Responses of nematode abundances to increased and reduced rainfall under field conditions: A meta‐analysis

“…However, it appears that the benefit of increased rainfall may take longer to manifest given the higher total abundances and more plant parasitic nematodes observed in the longer term experiments only. This is likely because reductions in rainfall have more immediate impacts on nematodes due to increased stress as well as longer term indirect effects through changes in resource availability, whereas increased water availability is more likely to predominantly have longer term impacts due to enhanced resource availability (Golluscio et al, 1998; Guan et al, 2019). However, the effects of rainfall changes will also be moderated by antecedent rainfall conditions at the study site irrespective of longer term rainfall (Nielsen & Ball, 2015).…”

“…Similarly, microbial grazers will respond to the increase in bacterial and fungal biomass and activity in the longer term, but this relationship may take longer to manifest. However, increased abundances of plant parasitic nematodes would lead to heightened feeding on plant roots, which could reduce plant growth and thereby suppress effects at higher trophic levels (Guan et al, 2019). Similarly, an increase in feeding activities of microbial grazers could suppress microbial biomass and activity, resulting in weaker responses to increased rainfall (Nielsen, 2019).…”

“…Most ecosystems studied were drylands and grasslands where primary productivity is already water‐limited (Knapp et al, 2020; Maranhão et al, 2018) and the abundance of soil fauna communities is expected to be similarly constrained by resource availability (Guan et al, 2019). While nematodes are generally considered relatively drought tolerant (Nielsen & Ball, 2015), our meta‐analysis shows that soil nematodes in drylands and grasslands will be severely negatively impacted by a further reduction in water availability, likely because resource availability is further exacerbated or due to stress‐driven mortality.…”

“…Omnivorous and predatory nematodes rely on the availability of resources that may be affected by water limitation and appear to be more sensitive to disturbance compared with other trophic groups (Krashevska et al, 2019), perhaps explaining why this group is so heavily impacted. Fungi are considered more drought resistant than bacteria (Barnard et al, 2013), which would suggest that resource availability for fungal feeders would be less impacted by reduced rainfall than other trophic groups (Guan et al, 2019), even if there are some direct negative effects of water stress (Wagner et al, 2015). However, few studies have assessed the effects on fungal feeders and fungal biomass simultaneously, making it difficult to test this assumption.…”

“…In recent years, however, there has been increasing interest in belowground biotic responses given their importance to ecosystem functions (Kojima et al, 2014;van den Hoogen et al, 2019). Among soil biota, nematodes are an ideal study group as they are very abundant, highly diverse, represent multiple trophic levels, and regulate soil processes through their interactions with plants, microbes, and other soil fauna (Guan et al, 2019). Understanding how nematodes are impacted by climate change is therefore important to predicting changes in ecosystem functions under future conditions (Papatheodorou et al, 2012).…”