Thirteen decades of foliar isotopes indicate declining nitrogen availability in central North American grasslands.
New Phytol
; 187(4): 1135-1145, 2010 Sep.
Article
em En
| MEDLINE
| ID: mdl-20553396
ABSTRACT
*Humans are increasing both the deposition of reactive nitrogen (N) and concentrations of atmospheric CO(2) 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(15)N 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(15)N 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 CO(2).
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Isótopos de Carbono
/
Ecossistema
/
Folhas de Planta
/
Ciclo do Nitrogênio
/
Poaceae
/
Nitrogênio
/
Isótopos de Nitrogênio
Tipo de estudo:
Prognostic_studies
Limite:
Humans
País/Região como assunto:
America do norte
Idioma:
En
Ano de publicação:
2010
Tipo de documento:
Article