Elevated CO2 increases fungal-based micro-foodwebs in soils of contrasting plant species

Abstract

As different plant species support different soil communities, assessment of climate change impacts on soil communities must consider how these impacts depend on the vegetation. We investigate soil community responses to global change under different co-occurring plant species. In a heathland FACE-experiment, we modelled projected global changes by increasing atmospheric CO2 concentration (to 510 ppm) and soil temperature by 1 °C at 2 cm depth (with night-time reflectance curtains) and reducing summer precipitation for 2–5 weeks annually (with rain-out curtains). We assessed nematode community trophic composition and bacterial and fungal abundance in soil under the dominant plant species Calluna vulgaris and Deschampsia flexuosa in the spring, 10 months after the last experimental drought period. Fungal dominance increased relative to bacterial under elevated CO2. Similarly, elevated CO2 increased abundance of fungivorous nematodes relative to bacterivorous nematodes. Decreased precipitation did not affect the abundances of microorganisms or nematodes, and there were only few effects of warming. Fungivorous nematodes dominated under C. vulgaris, whereas bacterivorous nematodes were relatively more abundant under D. flexuosa. Abundances of plant feeding and omnivorous/predatory nematodes were higher under D. flexuosa than under C. vulgaris. This supports the hypothesis that more carbon will flow through fungal than bacterial channels when below-ground allocation of photosynthetically-derived C increases without a corresponding soil nitrogen increase. Further, as different plant species are associated with distinct belowground decomposer communities, vegetation shifts induced by future CO2 and climate regimes will also shift belowground communities with consequences for decomposition dynamics.