With summer drought frequency expected to increase with climate change, there is a need to understand the mechanisms that determine the ability of soil functions to resist and recover from disturbance events. Many soil functions are regulated by soil organisms and understanding how the soil food web is impacted by global change is critical. We hypothesized that land management alters the structure of the soil food web, and that this in turn influences its response to and ability to recover from drought. We also expected that these changes would lead to differences in N and C uptake by plants and can drive the impact of drought on C and N transfer to microbes and other soil organisms. Drought shelters, alongside controls plots, were installed for 2 months at three sites of paired intensively and extensively managed grasslands in the Yorkshire Dales, northern England. After the shelters were removed, 15NO3 was injected into soil, and plants were pulse labelled with 13CO2. We assessed the fate of the 13C and 15N by sequential sampling over 20 days of plant tissue, soil bacterial and fungal PLFA, microarthropods and greenhouse gas fluxes.
Results/Conclusions
The results show that fixation of 13C by plants was dependent on management intensity and drought: plant shoots in intensively managed droughted systems fixed more 13C than control plants, whereas there were no differences in the extensively managed sites. The results show lower uptake of 15N by plant roots under drought condition, whatever the management, but similar concentrations of 15N in shoots among all treatments. In general, there was substantial variation in 13C and 15N enrichment of roots between sites. The initial results of the most abundant groups of microarthropods, i.e collembolans and mites, show a general pattern of higher 13C and 15N uptake in extensively compared to intensively managed grasslands, and a lower uptake of 13C and 15N under drought; but the trend depended on the group and trophic level of microarthropods. Analysis of 13C and 15N content PLFAs, which are ongoing, will allow us to link plant C and N uptake to specific components of the microbial community. These data will enable us to calculate C and N fluxes in different managed grassland in line with their food web structure and to see how these fluxes respond to a drought perturbation. Overall, our results indicate that intensive management may impair the resistance and resilience of soil food webs to drought.