Malcomb Jacob D, Epstein Howard E, Vadeboncoeur Matthew A, Druckenbrod Daniel L, Lanning Matthew, Wang Lixin, Asbjornsen Heidi, Scanlon Todd M
Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA.
Earth Systems Research Center, University of New Hampshire, Durham, NH, USA.
Oecologia. 2025 Jul 29;207(8):137. doi: 10.1007/s00442-025-05753-w.
Both theory and observations suggest that tree intrinsic water use efficiency (iWUE)-the ratio of photosynthetic carbon assimilation to stomatal conductance to water-increases with atmospheric CO. However, the strength of this relationship varies across sites and species, prompting questions about additional physiological constraints and environmental controls on iWUE. In this study, we analyzed tree core carbon isotope ratios to examine trends in, and drivers of, iWUE in 12 tree species common to the temperate forests of eastern North America, where forests have experienced changes in CO, climate, and atmospheric pollution in recent decades. Across all site-species combinations, we found that tree iWUE increased 22.3% between 1950 and 2011, coinciding with a 25.2% increase in atmospheric CO. iWUE trajectories varied markedly among tree functional groups and within species across sites. Needleleaf evergreen iWUE increased until circa 2002 before declining in recent years, while iWUE of broadleaf deciduous species continued to increase. The analysis of environmental controls on iWUE trends revealed smaller increases in iWUE in trees subjected to higher atmospheric pollution loads. Our results suggest that tree functional characteristics and atmospheric pollution history influence tree response to atmospheric CO, with implications for forest carbon and water balance in temperate regions.
理论和观测均表明，树木的内在水分利用效率（iWUE）——光合碳同化与气孔导水率之比——会随着大气二氧化碳浓度升高而增加。然而，这种关系的强度因地点和物种而异，这引发了关于iWUE的其他生理限制因素和环境控制因素的问题。在本研究中，我们分析了树木芯部的碳同位素比率，以研究北美东部温带森林中12种常见树种的iWUE趋势及其驱动因素，近几十年来，这些森林经历了二氧化碳浓度、气候和大气污染的变化。在所有地点-物种组合中，我们发现树木的iWUE在1950年至2011年间增加了22.3%，与此同时大气二氧化碳浓度增加了25.2%。iWUE轨迹在不同树木功能组之间以及同一物种内的不同地点之间存在显著差异。针叶常绿树的iWUE在2002年左右之前增加，近年来下降，而阔叶落叶树种的iWUE持续增加。对iWUE趋势的环境控制因素分析表明，遭受较高大气污染负荷的树木的iWUE增幅较小。我们的结果表明，树木功能特征和大气污染历史会影响树木对大气二氧化碳的响应，这对温带地区森林的碳和水平衡具有重要意义。
