Structure and functioning of soil animal food webs across temperate and tropical forests

Soil biogeochemical cycles are regulated by soil food webs. However, variation of soil food web structure and functioning across key environmental gradients remains unknown, hampering generalisations of any suggested links between fauna and biogeochemistry. Here, we used two complementary approaches to quantify soil animal food web variation across forest types, from southern taiga to rainforests. First, we applied the energy flux approach to explore patterns of energy distribution across micro-, meso- and macrofauna. We showed that tropical soil food webs have consistently higher energy flux, proportionally higher predation rates (31 vs 18-27% of the total energy flux) and relied more on the plant energy channel (21 vs 10%), but less on the bacterial (5 vs 9-18%) and litter energy channels (14 vs 18-32%), than temperate soil food webs. Second, we compiled a large database (>8000 records) of stable isotope composition of soil animals to see how detritivory and microbivory in soil animal communities change with environmental temperature and litter quality. Despite little effect of temperature, shift in ¹⁵N concentrations suggested that in most cases low litter quality (high %C and low %N) result in a switch from feeding directly on litter to feeding on microorganisms. Thus, soil animals change their functional role from competitors to consumers of microbes. Our studies show how the functioning of soil animal food webs changes across biomes with different climate and litter quality and summarise functional roles animals play in different biomes.