Drought and intensive management interact to alter soil food web stability and pathways of energy fluxes

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Abstract
Soil food webs contribute significantly to ecosystem carbon fluxes, but how carbon flux through them is affected by both intensification of land management and climate extremes, such as drought, is poorly understood and quantified. Here, we quantified in situ the energetics of soil food webs under experimental drought across grasslands with contrasting management intensity, which allowed us to test how management shapes the response to drought. Immediately after drought, total ecosystem respiration and food web energy fluxes were reduced relative to controls, whereas the fungal to bacterial energy flux ratio increased. Intensive management affected all these variables but affected only the responses of some of these variables to drought. Food web stability was also affected, with increased return time under intensive management and drought. Although we found that soil moisture, ecosystem respiration, stability, and food web and fungal to bacterial energy flux recovered after two months, nematodes and bacteria remained negatively impacted, while all other microarthropod groups increased. These findings show that while total fluxes and dynamical stability may have recovered from the drought, both community structure and pathways of energy flux remained sensitive to past drought. These long-lasting effects may be critical in regulating pathways of below-ground carbon flux and ecosystem carbon emissions from soil.