Global change effects on plant-soil interactions

As plants of different life-forms generate different soil communities, assessment of climate change impacts on soil communities and soil services must consider how these impacts are conditioned by the vegetation above. We investigated how soil communities under different plant species in the same ecosystem respond to global change. In a heathland FACE-experiment, we modelled projected global changes in the field i.a. by increasing CO2 and temperature. We assessed trophic composition of nematode communities and abundance of bacteria and fungi (by qPCR) in rhizospheres of the two dominant plant species Calluna vulgaris (dwarf shrub) and Deschampsia flexuosa (grass). Fungivores dominated nematode communities under C. vulgaris, whereas relative abundances of bacterivores, herbivores, and omnivores were all significantly higher under D. flexuosa. Elevated CO2 stimulated fungivores and increased their abundance relative to bacterivores under both plant species. The pattern was similar for microorganisms; fungal dominance generally increased relative to bacterial under elevated CO2.This corresponds with the hypothesis that when CO2 available for photosynthesis increases without a corresponding increase of soil nitrogen, more carbon will flow through fungal rather than bacterial channels. Warming modified the effect of elevated CO2 on the fungivore abundance, but with a different outcome under the two plant species. Together, these results indicate that decomposition at future CO2 levels may to a greater extent be mediated by fungi. With the corresponding increase in temperature, however, this effect will depend on plant species