Transient and cumulative impacts of experimental increases in temperature and N-deposition in subalpine meadows

This study reports on a three-year long experiment that examines the role of grazing, soil warming, and N-deposition on ecosystem processes, including aboveground net primary production (ANPP), N-availability, soil respiration, and soil C and N stocks. The primary question this study addresses is whether there is an interaction between local land use (livestock grazing) and regional or global changes (warming and nitrogen deposition). A secondary question was whether warming and N-deposition lead to changes in the distribution of C within the plant-soil system that could alter total ecosystem C stocks. I initially found a strong interaction between grazing and warming in rates of soil respiration, but this response was transient and by the third year warming had the same impact on both grazed and ungrazed plots. In contrast to this transient effect, temperature impact on N availability was cumulative, with N availability increasing in response to warming with each year of the treatment. There was a strong effect of livestock grazing on ANPP that did not interact with temperature treatments. These data suggest that for some ecosystem characteristics, human influences may be additive, but as often there will be interactions between local land-use decisions and global drivers.