Articles | Volume 2, issue 4
https://doi.org/10.5194/soil-2-565-2016
https://doi.org/10.5194/soil-2-565-2016
Review article
 | 
01 Nov 2016
Review article |  | 01 Nov 2016

Soil fauna: key to new carbon models

Juliane Filser, Jack H. Faber, Alexei V. Tiunov, Lijbert Brussaard, Jan Frouz, Gerlinde De Deyn, Alexei V. Uvarov, Matty P. Berg, Patrick Lavelle, Michel Loreau, Diana H. Wall, Pascal Querner, Herman Eijsackers, and Juan José Jiménez

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 fauna controls almost any aspect of organic matter turnover, foremost by regulating the activity and functional composition of soil microorganisms and their physical–chemical connectivity with soil organic matter. We demonstrate a very strong impact of soil animals on carbon turnover, increasing or decreasing it by several dozen percent, sometimes even turning C sinks into C sources or vice versa. This is demonstrated not only for earthworms and other larger invertebrates but also for smaller fauna such as Collembola. 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 soil fauna is essential to make realistic modelling predictions on SOM dynamics and to detect expected non-linear responses of SOM dynamics to global change. We present a decision framework, to be further developed through the activities of KEYSOM, a European COST Action, for when mechanistic SOM models include soil fauna. The research activities of KEYSOM, such as field experiments and literature reviews, together with dialogue between empiricists and modellers, will inform how this is to be done.

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Short summary
Soils store more than 3 times as much carbon than the atmosphere, but global carbon models still suffer from large uncertainty. We argue that this may be due to the fact that soil animals are not taken into account in such models. They dig, eat and distribute dead organic matter and microorganisms, and the quantity of their activity is often huge. Soil animals affect microbial activity, soil water content, soil structure, erosion and plant growth – and all of this affects carbon cycling.