The major route of C into soils is through plant material, either as plant root exudates or decomposing organic matter. The quality and quantity of C entering below-ground ecosystems are generally controlled through agricultural management practices driving changes in the above-ground botanical composition. Soil food webs are based on three different carbon pools - root exudates, litter, and recalcitrant soil organic matter. It is thought that these create three distinct energy channels in the soil food web and are thus critical in controlling soil community compositional dynamics and also many of those soil functions considered desirable in healthy soils. Although the relative size of the 'living' soil C pool (the microbial biomass) is small compared to the total C pool, it is the former that is important in facilitating the cycling of nutrients in the soil. We will be testing how changes in the quality and quantity of carbon entering the soil are driven by changes in plant species composition and that such changes impact on soil communities and the functions that they perform. We will study:

1. the mechanism of C movement from the plant into soil food webs, both the relative importance of exudation and litter inputs and how management (including root herbivory) influences this;
2. the relative importance of the different feeding (energy) channels in the soil and how they interact with soil functions;
3. the relative importance of biotic and abiotic modifiers of C turnover and how it changes with scale;
4. how management and soil type influence rhizosphere community selection by plants.

We will utilise soils from different managements (from Highfield, Rowden and other long-term experiments) using an approach based around a range of small scale (mesocosm - plot) manipulative studies. We will utilise stable isotopes to trace and define nutrient fluxes in the soil communities and, combined with taxonomy, standard process measurements, and molecular and phenotypic profiling techniques, will examine the functional relationship between plants and the soil biota in grassland soils. The work is complemented by a 4 year BBSRC PhD project studying soil food webs. The research will deliver a mechanistic understanding of the role of the plant in driving / regulating below-ground communities in grassland soils and data to populate food web and other models currently being developed. The work also aims to explore the potential to develop a conceptual model outlining the simplest basic rules of temporal and spatial interactions between substrates and food web components.