School of Geography and Tourism, Shaanxi Normal University, Xi'an, China.
State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China.
Tree Physiol. 2019 Jan 1;39(1):88-103. doi: 10.1093/treephys/tpy060.
Tree-ring δ13C and δ18O of dominant Dahurian larch and Mongolia pine in the permafrost region of the northern Great Higgnan Mountains, China were used to elucidate species-specific ecophysiological responses to warming temperatures and increasing CO2 over the past century. Larch and pine stable carbon discrimination (Δ13C) 13C and δ18O in tree rings both showed synchronous changes during the investigated period (1901-2010), but with species-specific isotopic responses to atmospheric enriched CO2 and warming. Tree-ring Δ13C and δ18O were controlled by both maximum temperature and moisture conditions (precipitation, relative humidity and vapor pressure deficit), but with different growth periods (Δ13C in June-July and δ18O in July-August, respectively). In addition, stable isotopes of larch showed relatively greater sensitivity to moisture deficits than pine. Climatic conditions from 1920 to 1960 strongly and coherently regulated tree-ring Δ13C and δ18O through stomatal conductance. However, climatic-sensitivities of tree-ring Δ13C and δ18O recently diverged, implying substantial adjustments of stomatal conductance, photosynthetic rate and altered water sources over recent decades, which reveal the varied impacts of each factor on tree-ring Δ13C and δ18O over time. Based on expected changes in leaf gas-exchange, we isolated the impacts of atmospheric CO2 and climate change on intrinsic water-use efficiency (iWUE) over the past century. Higher intracellular CO2 in pine than larch from 1960 onwards suggests this species may be more resilient to severe droughts in the future. Our data also illustrated no weakening of the iWUE response to increasing CO2 in trees from this permafrost region. The overall pattern of CO2 enrichment and climate impacts on iWUE of pine and larch were similar, but warming increased iWUE of larch to a greater extent than that of pine over recent two decades. Taken together, our findings highlight the importance of considering how leaf gas-exchange responses to atmospheric CO2 concentration influence species-specific responses to climate and the alteration of the hydrological environment in forests growing in regions historically dominated by permafrost that will be changing rapidly in response to future warming and increased CO2.
中国大兴安岭北部多年冻土区的优势树种兴安落叶松和樟子松的树轮δ13C 和 δ18O 被用来阐明过去一个世纪中物种对变暖温度和大气 CO2 增加的特定生态生理响应。在所研究的期间（1901-2010 年），落叶松和松树稳定碳分馏（Δ13C）和树木年轮 δ18O 都表现出同步变化，但对大气 CO2 富集和变暖有特定的同位素响应。树轮 Δ13C 和 δ18O 受最高温度和水分条件（降水、相对湿度和蒸气压亏缺）的共同控制，但生长周期不同（6 月至 7 月为 Δ13C，7 月至 8 月为 δ18O）。此外，落叶松的稳定同位素对水分亏缺的敏感性相对高于松树。1920 年至 1960 年的气候条件通过气孔导度强烈而一致地调节了树木年轮 Δ13C 和 δ18O。然而，近年来树木年轮 Δ13C 和 δ18O 的气候敏感性出现分歧，这意味着在过去几十年中，气孔导度、光合速率和水源发生了实质性的调整，这揭示了每个因素对树木年轮 Δ13C 和 δ18O 的随时间变化的不同影响。基于叶气体交换的预期变化，我们在过去一个世纪中分离了大气 CO2 和气候变化对内在水分利用效率（iWUE）的影响。1960 年以后，松树叶片内的细胞间 CO2 高于落叶松，这表明该物种在未来可能更能抵御严重干旱。我们的数据还表明，在这个多年冻土区的树木中，iWUE 对 CO2 增加的响应并没有减弱。CO2 富集和气候对松树和落叶松 iWUE 的综合影响模式相似，但在过去二十年中，变暖使落叶松的 iWUE 增加幅度大于松树。总的来说，我们的研究结果强调了考虑叶气体交换对大气 CO2 浓度的响应如何影响物种对气候的特定响应以及在历史上以多年冻土为主的森林水文环境变化的重要性，这些森林将因未来变暖而迅速变化并增加 CO2。
