Short term effects of climate change and intensification of management on the abundance of microbes driving nitrogen turnover in montane grassland soils

Montane grasslands in Europe are exposed to increasing temperatures twice as fast as the global average. Changes in climatic conditions are possibly accompanied by an increase in land use intensity, caused by a prolongation of the vegetation period and the need to improve productivity. Therefore, the investigation of combined effects of climate change and land use intensity is needed to further implement agricultural management strategies. Here we present results from a study performed in the pre-alpine region of southern Germany, where intact plant-soil mesocosms from grasslands, were translocated along an altitudinal gradient, resulting in an increase in soil temperature (moderate treatment: +0.5 K; strong treatment: +1.9 K warming) during the experimental period. Additionally, we applied an extensive or intensive agricultural management (two vs. five times of mowing and slurry application) on the transplanted mesocosms. After an exposure of one year, we measured plant growth and soil properties and quantified abundances of soil microorganisms catalyzing key steps in the nitrogen (N) cycle. Our data indicate, significant interactions between climate change and management. ... mehrFor example, microbial biomass was significantly reduced (−47.7% and −49.8% for C$_{mic}$ and N$_{mic}$ respectively), which was further accompanied by lower abundances of N$_{2}$-fixing bacteria (up to −89,3%), as well as ammonia oxidizing bacteria (−81.4%) under intensive management, whereas N-mineralizing bacteria increased in abundance (up to +139.8%) under extensive management. Surprisingly, the abundances of denitrifying bacteria as well as mean N$_{2}$O emissions were not affected by the treatments. Overall, our data suggest pronounced shifts in the abundance of microbes driving the N cycle in soil as a result of combined climate change and land use intensification already after a short simulation period of one year.