Elevated ozone and nitrogen deposition affect nitrogen pools of subalpine grassland

摘要

In a free-air fumigation experiment with subalpine grassland, we studied long-term effects of elevated ozone (O-3) and nitrogen (N) deposition on ecosystem N pools and on the fate of anthropogenic N. At three times during the seventh year of exposure, N pools and recovery of a stable isotope tracer (N-15) were determined in above- and belowground plant parts, and in the soil. Plants were much better competitors for N-15 than soil microorganisms. Plant N pools increased by 30-40% after N addition, while soil pools remained unaffected, suggesting that most of the extra N was taken up and stored in plant biomass, thus preventing the ecosystem from acquiring characteristics of eutrophication. Elevated O-3 caused an increase of N in microbial biomass and in stabilized soil N, probably resulting from increased litter input and lower litter quality. Different from individual effects, the interaction between the pollutants remained partly unexplained. (C) 2015 Elsevier Ltd. All rights reserved.