Soil fauna: key to new carbon models

Abstract. Soil organic matter (SOM) is key to maintaining soil fertility, mitigating climate change, combatting land degradation, and conserving above- and below-ground biodiversity and associated soil processes and ecosystem services. In order to derive management options for maintaining these essential services provided by soils, policy makers depend on robust, predictive models identifying key drivers of SOM dynamics. Existing SOM models and suggested guidelines for future SOM modelling are defined mostly in terms of plant residue quality and input and microbial decomposition, overlooking the significant regulation provided by soil fauna. The contribution of soil fauna activities to SOM decomposition can be as high as 40 %, as they control almost any aspect of organic matter turnover, foremost by regulating the activity and functional composition of soil microorganisms and their physico-chemical connectivity with soil organic matter. We suggest that inclusion of soil animal activities (plant residue consumption and bioturbation altering the formation, depth, hydraulic properties and physical heterogeneity of soils) can fundamentally affect the predictive outcome of SOM models. Understanding direct and indirect impacts of soil fauna on nutrient availability, carbon sequestration, greenhouse gas emissions and plant growth is key to the understanding of SOM dynamics in the context of global carbon cycling models. We argue that explicit consideration of the soil fauna is essential to make realistic modelling predictions on SOM dynamics and to detect expected non-linear responses to global change, and we suggest that guidelines for future SOM modelling should implement the role of soil fauna. Finally, we briefly introduce the new COST (European Cooperation in Science and Technology) Action ES 1406 (KEYSOM – Soil fauna: key to new carbon models) which brings together biogeochemists and soil ecologists from 21 EU countries. KEYSOM provides a research network for improved SOM models by implementing the role of the soil fauna as a basis for sustainable soil management. An interdisciplinary platform of experimentalists and modellers will assure better access to experimental data, identify the most burning research gaps and inform decision makers.