Dipartimento di Scienze Ambientali, Università di Parma, via G. P. Usberti 11, 43100, Parma, Italy.
Glob Chang Biol. 2012 Sep;18(9):2925-44. doi: 10.1111/j.1365-2486.2012.02757.x. Epub 2012 Jul 10.
The objective of this study is to globally assess the effects of atmospheric nitrogen deposition and climate, associated with rising levels of atmospheric CO2 , 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 CO2 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 between 1850 and 2000, with no evidence that the increased rate was reduced at higher ambient CO2 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 CO2 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 (Nrate ) and long-term cumulative (Ncum ) 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 Nrate with iWUE and Δ(13) C was observed in conifers and in the angiosperms, and Ncum was the only independent term with a significant positive association with iWUE, although a multi-factorial control was evident in conifers.
本研究旨在全面评估大气氮沉降和气候（与大气 CO2 浓度升高有关）对被子植物和针叶树物种碳同位素分馏（Δ(13) C）和内在水分利用效率（iWUE）变异性的影响。从文献中提取了 89 条长期同位素树木年轮年表，代表全球 53 个地点的 23 种针叶树和 13 种被子植物物种，用于获得长期的 Δ(13) C 和 iWUE 时间序列。将 Δ(13) C 和 iWUE 与工业时期大气 CO2 浓度的增加以及 1950-2000 年模拟大气氮沉降和气候变量的变化相关联。我们应用广义加性模型和线性混合效应模型来预测气候变量和氮沉降对 Δ(13) C 和 iWUE 的影响。结果表明，在工业时期，被子植物和针叶树物种的 Δ(13) C 呈下降趋势，1850 年至 2000 年间 iWUE 增加了 16.1%，但没有证据表明在较高的环境 CO2 值下，增加率降低。Δ(13) C 的时间变化支持了植物保持胞间和环境 CO2 浓度之间恒定比例的主动机制的假说。我们定义了线性混合效应模型，这些模型有效地描述了 Δ(13) C 和 iWUE 作为一组环境预测因子的变化，这些因子可以替代包括年速率（Nrate）和长期累积（Ncum）氮沉降。然而，没有单一的气候或大气变量具有明显的主导作用，但是 Δ(13) C 和 iWUE 显示出不同协变量之间复杂的依赖相互作用。在针叶树和被子植物中，Nrate 与 iWUE 和 Δ(13) C 之间存在显著的关联，而 Ncum 是与 iWUE 呈显著正相关的唯一独立项，尽管在针叶树中存在多因素控制。
