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.

Abstract. The spatial distribution of resources affects ecological processes at all levels of biological organization. However, it remains to be tested how the spatial configuration of belowground resources affects the community dynamics of soil organisms and resulting plant–soil feedbacks. We used Agrostis stolonifera plants in different spatial configurations in mesocosms to study the dispersal patterns of soil nematodes and rotifers. Plant–soil feedbacks were later assessed by re-sowing the mesocosms with Lolium perenne and Plantago lanceolata after removing all the initial A. stolonifera plants from the mesocosms. Bacterial-feeding nematodes and rotifers spread fast, whereas plant-feeding nematodes barely dispersed from the release sites. These spread patterns of nematodes and rotifers depended on the life-history traits and not on the spatial pattern of the plants. However, more clustered plants developed a higher total biomass and caused a reduced growth of the subsequent vegetation. Our results demonstrate that the mere spatial pattern of a single plant species can alter the strength of plant–soil feedbacks. This has important implications for understanding the impact of planting or replanting schemes and other changes in the spatial configuration of plants on long-term vegetation development and succession.

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<p>Soil, the living skin of the Earth, provides ecosystem services critical for life: soil acts as a water filter and a growing medium, offers habitat for billions of organisms, and supplies most of the antibiotics. In places, it may take a hundred years to form one cm of soil, but it can be degraded only in a few years or less by a number of natural and anthropogenic factors, including climate change. Presently, one third of all land is degraded to some extent, and fertile soil is lost every year. Droughts are becoming more common, also in humid climates, and the combination of erratic weather patterns with an increased pressure on land by human activities leads to soil degradation. Soil degradation results in a loss of fertile topsoil, thereby altering the soil hydrology completely. As the consequences, soil water holding capacity decreases, hydrophobicity increases, and more runoff is observed, that leads to further soil degradation. Thus, soil hydrology is the key for a healthy functioning topsoil/soil ecosystem. We are in urgent need for novel solutions for improving soil hydraulic properties that will lead to restoration of degraded soils.</p><p>In this study we investigate a possibility of restoring degraded soil using microorganisms. The hypothesis is that microorganisms can improve soil hydraulic properties such as infiltration and water retention, and reduce hydrophobicity that will facilitate further ecosystem restoration. Such strategy is based on combining the research fields of microbiology and soil physics that to date have hardly been combined. To test this hypothesis, we have inoculated sandy soil with a bacterium Bacillus mycoides and then measured its hydraulic properties using evaporation and pressure plate methods. We have also made efforts of standardizing this methodology by testing incubation time and inoculum concentrations on the hydraulic properties of the soil. Evaluation of an effect of bacteria addition on the soil water holding capacities and unsaturated water conductivity have been conducted as a comparison between inoculated soil and uninoculated (control). Results of this ongoing study will be presented here.</p>