期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2019
卷号：116
期号：7
页码：2749-2754
DOI：10.1073/pnas.1816686116
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Due to anthropogenic emissions and changes in land use, trees are now exposed to atmospheric levels of [ C O 2 ] that are unprecedented for 650,000 y [Lüthi et al. (2008) Nature 453:379–382] (thousands of tree generations). Trees are expected to acclimate by modulating leaf–gas exchanges and alter water use efficiency which may result in forest productivity changes. Here, we present evidence of one of the strongest, nonlinear, and unequivocal postindustrial increases in intrinsic water use efficiency ( i W U E ) ever documented (+59%). A dual-isotope tree-ring analysis ( δ 13 C and δ 18 O ) covering 715 y of growth of North America’s oldest boreal trees ( Thuja occidentalis L.) revealed an unprecedented increase in i W U E that was directly linked to elevated assimilation rates of C O 2 (A). However, limited nutrient availability, changes in carbon allocation strategies, and changes in stomatal density may have offset stem growth benefits awarded by the increased i W U E . Our results demonstrate that even in scenarios where a positive C O 2 fertilization effect is observed, other mechanisms may prevent trees from assimilating and storing supplementary anthropogenic emissions as above-ground biomass. In such cases, the sink capacity of forests in response to changing atmospheric conditions might be overestimated.
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