Historic nitrogen deposition determines future climate change effects on nitrogen retention in temperate forests

Nitrogen (N) cycle processes in terrestrial ecosystems are highly sensitive to temperature and soil moisture variations. Thus, future climate change may affect the degree to which N deposited from the atmosphere will be retained in forest ecosystems. We evaluated the effect of future changes in climate and N deposition on ecosystem N cycling using the model LandscapeDNDC forced with historical data from eight long-term forest ecosystem monitoring stations in Austria and downscaled future N deposition and climate scenarios. With every 1 °C of warming, annual N uptake in biomass increased by +0.03 to +0.54 kg N ha −1 , total soil organic matter (SOM) increased annually by +0.003 to +0.08 kg N ha −1 , and mean annual N leaching was between −0.09 and −2.03 kg N ha −1 lower. The magnitude of N deposition in the years from 1990 to 2010 was by far the most important determinant of the response of nitrogen cycling to future warming, including statistically significant relationships with humus N content and N leaching. We conclude that climate change will likely increase ecosystem N retention in temperate forest ecosystems, and even more so at forest sites with high past N deposition.