期刊
NEW PHYTOLOGIST
卷 187, 期 4, 页码 1135-1145出版社
WILEY
DOI: 10.1111/j.1469-8137.2010.03322.x
关键词
grasslands; herbarium; isotopes; Kansas; nitrogen deposition
资金
- National Science Foundation [EPSCoR 0553722]
- Kansas Technology Enterprise Corporation
P>Humans are increasing both the deposition of reactive nitrogen (N) and concentrations of atmospheric CO2 on Earth, but the combined effects on terrestrial ecosystems are not clear. In the absence of historical records, it is difficult to know if N availability is currently increasing or decreasing on regional scales. To determine the nature and timing of past changes in grassland ecosystem dynamics, we measured the composition of stable carbon (C) and N isotopes in leaf tissue from 545 herbarium specimens of 24 vascular plant species collected in Kansas, USA from 1876 to 2008. We also parameterized a simple model of the terrestrial N cycle coupled with a stable isotope simulator to constrain processes consistent with observed patterns. A prolonged decline in foliar N concentrations began in 1926, while a prolonged decline in foliar delta 15N values began in 1940. Changes in the difference between foliar and atmospheric C isotopes reveal slightly increased photosynthetic water use efficiency since 1876. The declines in foliar N concentrations and foliar delta 15N suggest declining N availability in these grasslands during the 20th century despite decades of anthropogenic N deposition. Our results are consistent with progressive-nitrogen-limitation-type hypotheses where declines in N availability are driven by increased ecosystem N storage as a result of increased atmospheric CO2.
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