Publication Date:
2012-06-03
Description:
The objective of this study is to globally assess the effects of atmospheric nitrogen deposition and climate, associated with rising levels of atmospheric CO 2 , on the variability of carbon isotope discrimination ( Δ 13 C) and intrinsic water-use efficiency ( iWUE ) of angiosperm and conifer tree species. Eighty-nine long-term isotope tree-ring chronologies, representing 23 conifer and 13 angiosperm species for 53 sites worldwide, were extracted from the literature, and used to obtain long-term time series of Δ 13 C and iWUE . Δ 13 C and iWUE were related to the increasing concentration of atmospheric CO 2 over the industrial period (1850-2000) and to the variation of simulated atmospheric nitrogen deposition and climatic variables over the period 1950-2000. We applied generalized additive models and linear mixed-effects models to predict the effects of climatic variables and nitrogen deposition on Δ 13 C and iWUE . Results showed a declining Δ 13 C trend in the angiosperm and conifer species over the industrial period and a 16.1% increase of iWUE by between 1850 and 2000, with no evidence that the increased rate was reduced at higher ambient CO 2 values. The temporal variation in Δ 13 C supported the hypothesis of an active plant mechanism that maintains a constant ratio between intercellular and ambient CO 2 concentrations. We defined linear mixed-effects models that were effective to describe the variation of Δ 13 C and iWUE as a function of a set of environmental predictors, alternatively including annual rate ( N rate ) and long-term cumulative ( N cum ) nitrogen deposition. No single climatic or atmospheric variable had a clearly predominant effect, however Δ 13 C and iWUE showed complex dependent interactions between different covariates. A significant association of N rate with iWUE and Δ 13 C was observed in conifers and in the angiosperms, and N cum was the only independent term with a significant positive association with iWUE, while a multi-factorial control was evident in conifers.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
,
Energy, Environment Protection, Nuclear Power Engineering
,
Geography
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