Effects of environmental warming and drought on size-structured soil food webs

Soil systems maintain important ecosystem processes crucial for plant life and food production. Especially agricultural systems are strongly affected by climate change due to low vegetation cover associated with high temperatures and drought. Nevertheless, the response of soil systems to climate change is little explored. We used microcosms with a simplified soil community to address effects of climate change using independent temperature and dryness gradients and addressed their effects on top-down control and litter decomposition. The community consisted of maize litter as a basal resource, fungi, springtails and as top predators mites and centipedes. As the body-size structure is of high importance for communities, we included differently-sized springtails and predator species. After seven weeks, the experiment was terminated, and the impact of climate change on direct feeding interactions and indirect effects across trophic levels was analysed. With increasing temperature and dryness, consumption rates increased, thereby amplifying the negative influence of consumer populations on their resources. Hence, these climate-change variables increased the top-down control of 1) predators (mainly mites) on springtails and 2) fungi on litter decomposition. In addition, we found that the climate-change variables strengthened trophic cascades from predators on fungi whose density was thus increasingly decoupled from top-down control by their springtail consumers. Their increased decomposition rates are of high importance for carbon cycling and may result in accelerated nutrient turnover. In conclusion, our results suggest that climate change may strongly influence the structure and functioning of soil systems by strengthening consumption rates and trophic cascades, which will have far reaching consequences for the nutrient turnover and productivity of agricultural ecosystems.