Disentangling microbial decomposition networks : linking detritus-based soil microbial food webs to ecosystem processes

Soils are crucial for a large number of ecosystem services and occupy an important position in driving the Earth’s biogeochemical cycles. Soils are therefore essential for e.g. agricultural food production, carbon sequestration, water purification and nutrient cycling. These soil functions are to a large extent governed by the huge biodiversity of soil life, which can be depicted in the form of a soil food web: a model that describes the feeding relationships among groups of species that live in the soil. A number of soil ecosystem services, as governed by soil life, are currently under considerable threat due to e.g. soil degradation, atmospheric nitrogen deposition and land use change. A proper understanding of the mechanisms underlying soil ecosystem functioning, in relation to global change, is important to anticipate these threats and to help ensure optimal functioning of our soils. Soil food web models have proven to be highly useful in the study of the long-term consequences of environmental change on soil communities and associated ecosystem functioning. Perhaps the most important ecosystem process driven by the soil food web is the decomposition of detritus: plant residues and soil organic matter. Via the decomposition of detritus, soil organisms determine the critical balance between sequestration and mineralization of carbon (C) and nutrients, affecting soil CO2 emissions to the atmosphere and nutrient availability for plants. Soil microbes (bacteria, fungi and protozoa) play a very important role in the decomposition of detritus by being the first consuming trophic level and by making up more than 90% of the total belowground biomass. In this way, soil microbes are the main influencers of C and nitrogen (N) dynamics in soil. However, detailed information on the microbial processing of different types of organic substrates in soil food webs is still missing. Due to the important role of soil microbial communities in C and N cycling, this information is cr