Differentiating between root- and leaf-litter controls on the structure and stability of soil micro-food webs

Abstract The dynamics of soil food webs play a key role in determining the ecological response of terrestrial ecosystems to current and future environmental change. Both root and leaf litter fuel the micro-food webs (microorganisms and nematodes) in soil, but whether the root and leaf litter would favor different components of the micro-food webs is not clear, especially the relative importance of these two litter sources on the stability of the micro-food web. We compared micro-food webs in mineral soils without added litter, with added leaf litter and with added root litter and investigated the effect of the litter carbon source on the resistance of the micro-food webs to added nitrogen and added nitrogen and phosphorus. The nematode community was more sensitive than the microbial community to the carbon source. Root litter was favored by bacteria, and leaf litter was preferred by fungi. Herbivorous nematodes were controlled more by the input of leaf litter than the input of root litter. Fertilization increased the effects of the root litter on the structure of the nematode community and thus moderated the effects of the litter source on the micro-food web. When both nitrogen and phosphorus were added, the root litter fueled the more resistant first trophic level (microorganisms), and the leaf litter fueled the more adaptable second trophic level (nematodes). Our results suggest that the input of leaf litter would be more important than the input of root litter for promoting a conservative cycling of nutrients and more positive soil feedback effects on plant growth. Our results also indicate that leaf litter and root litter help micro-food webs to adapt to exogenous disturbance in different ways, which would aid our mechanistic understanding of how soil food webs and their associated ecosystem processes would respond to current and future environmental changes.