Stepping N-to the Past: Plant Responses to Anthropogenic Nitrogen Deposition

Abstract

Anthropogenic nitrogen (N) deposition has doubled the amount of N entering the biosphere. To quantify the historical effect of N deposition on plant N uptake, we sampled long-term herbaria collections from the Bell Museum of Natural History. We expected that plants would increase leaf N and 15N:14N ratios as a result of increasing soil N availability. Contrary to our hypothesis, the 15N:14N ratios decreased over the last 120 years for both Acer and Betula. Betula leaf N content decreased through time; Acer leaf N had no response. These results suggest that anthropogenic N deposition may not be the only factor to influence soil N availability over the last century.