Global change agents interactively affect soil organisms with possible impacts on ecosystem functions
Soils store ~80% of global terrestrial organic carbon and alterations in fluxes into and out of this pool may interact with ongoing climate change. Little is known about the responses of belowground food webs driving soil C dynamics to co-occurring global change agents. To realistically predict global change scenarios, ambient and elevated atmospheric CO2concentration, ambient and enriched nitrogen input, and ambient and reduced summer precipitation were investigated in a long-term study (13 years) to evaluate how these agents affect soil processes by utilizing nematodes as indicator group of soil food web structure.
The density of fungal feeders increased considerably in response to N addition, but this effect was alleviated by elevated CO2. Nematode community analysis suggested that the decomposer community switched from bacterial-dominated to a fungal-dominated system at elevated N, indicating shifts in the microbial community as well as in the functioning of belowground food webs. Reduced densities of root-feeding Longidoridae at elevated CO2 and elevated N suggest increased plant performance and lower susceptibility to herbivores. Predacious nematodes were less abundant at elevated N, and changes in nematode community structure suggest reduced top-down forces and simplified soil food webs. At elevated CO2 top-down forces were strengthened as the density of bacterial-feeding nematodes did not change despite increased belowground carbon flow. The studied global change agents interactively and differentially affected functional guilds of soil nematodes, suggesting complex changes in soil processes with decomposition processes shifting towards the fungal channel at elevated N. Overall, the results indicate that shifts in soil food web structure may cause distinct changes in ecosystem functioning.