Toward a Complete Soil C and N Cycle: Incorporating the Soil Fauna

Abstract

Increasing pressures on ecosystems through global climate and other land-use changes require predictive models of their consequences for vital processes such as soil carbon and nitrogen cycling. These environmental changes will undoubtedly affect soil fauna. There is sufficient evidence that soil fauna have significant effects on all of the pools and fluxes in these cycles, and soil fauna mineralize more N than microbes in some habitats. It is therefore essential that their role in the C and N cycle be understood. Here we introduce a new framework that attempts to reconcile our current understanding of the role of soil fauna within the C and N cycle with biogeochemical models and soil food web models. Using a simple stoichiometric approach to integrate our understanding of N mineralization and immobilization with the C:N ratio of substrates and faunal life history characteristics, as used in food web studies, we consider two mechanisms through which soil fauna can directly affect N cycling. First, fauna that are efficient assimilators of C and that have prey with similar C:N ratios as themselves, are likely to contribute directly to the mineral N pool. Second, fauna that are inefficient assimilators of C and that have prey with higher C:N ratios than themselves are likely to contribute most to the dissolved organic matter (DOM) pool. Different groups of fauna are likely to contribute to these two pathways. Protists and bacteria-feeding nematodes are more likely to be important for N mineralization through grazing on microbial biomass, while the effects of enchytraeids and fungal-feeding microarthropods are most likely to be important for DOM production. The model is consistent with experimental evidence and, despite its simplicity, provides a new framework in which the effects of soil fauna on pools and fluxes can be understood. Further, the model highlights our gaps in knowledge, not only for effects of soil fauna on processes, but also for understanding of the soil C and N cycle in general.

Soil-atmosphere greenhouse gases (CO₂, CH₄ and N₂O) exchange in evergreen oak woodland in southern Portugal

“…Therefore the response to temperature did not follow an Arrhenius-type relation with rising temperature in dry period. A positive correlation between soil CH 4 and CO 2 in our study may be explained by the close links between C and N cycles involving microorganisms that contribute directly to CO 2 , N 2 O and CH 4 fluxes (Osler and Sommerkorn 2007).…”

Landscape-Scale Implications of the Edge Effect on Soil Fauna Activity in a Temperate Forest

“…Soil fauna are key contributors to soil and litter respiration, they breakdown and recycle organic material, affect microbial activity, and are important ecosystem engineers (Seastedt 1984;Hassall and others 2006;Lavelle and others 2006;Osler and Sommerkorn 2007;Kampichler and Bruckner 2009). Temperature and moisture are the main drivers determining the activity and density of the soil fauna (Liiri and others 2002;Gongalsky and others 2008;Makkonen and others 2011), with reduced abundance and activity being found at the forest edges compared with the forest core (Haskell 2000;Simpson and others 2012).…”

Quantifying Food Web Flows Using Linear Inverse Models

“…The food web topology and the associated parameters are taken from a recent study on the effects of fauna on C and N cycling in soils by Osler and Sonimerkorn (2007). The food web includes 5 compartments that are linked with 14 C and N flows (Figure 3).…”