CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, 72 Wenhua Road, Shenhe, Shenyang, Liaoning, China.
Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford St., Cambridge, MA, USA.
Tree Physiol. 2018 Jul 1;38(7):1041-1052. doi: 10.1093/treephys/tpy001.
Stomatal conductance (gs) generally decreases under elevated CO2 concentration (eCO2) and its sensitivity varies widely among species, yet the underlying mechanisms for these observed patterns are not totally clear. Understanding these underlying mechanisms, however, is critical for addressing problems regarding plant-environment interactions in a changing climate. We examined gs, water transport efficiency of different components along the whole-plant hydraulic system and allometric scaling in seedlings of six tree species grown under ambient and eCO2 treatments (400 and 600 ppm, respectively). Growth under eCO2 caused gs to decrease in all species but to highly variable extents, ranging from 13% (Populus tremuloides Michx.) to 46% (Gymnocladus dioicus (L.)). Accompanying this significant decrease in gs, substantial changes in plant hydraulic architecture occurred, with root hydraulic conductance expressed both on leaf area and root mass bases overall exhibiting significant decreases, while stem and leaf hydraulic efficiency either increased or showed no consistent pattern of change. Moreover, significant changes in allometry in response to eCO2 affected the whole-plant water supply and demand relations. The interspecific variation in gs response among species was not correlated with relative changes in stem and leaf hydraulic conductance but was most strongly correlated with the relative change in the allometric scaling between roots and leaves, and to a lesser extent with the intrinsic root hydraulic conductance of the species. The results underscore that allometric adjustments between root and leaf play a key role in determining the interspecific sensitivity of gs responses to eCO2. Plant hydraulics and their associated allometric scaling are important changes accompanying gs responses to eCO2 and may play important roles in mediating the interspecific variations of leaf gas exchange responses, which suggests that mechanistic investigations regarding plant responses to eCO2 need to integrate characteristics of hydraulics and allometric scaling in the future.
气孔导度（gs）通常在高二氧化碳浓度（eCO2）下降低，其敏感性在物种间差异很大，但这些观察到的模式的潜在机制尚不完全清楚。然而，理解这些潜在的机制对于解决气候变化中植物-环境相互作用的问题至关重要。我们研究了在大气和 eCO2 处理（分别为 400 和 600 ppm）下生长的六种树种幼苗的 gs、整个植物水力系统不同组成部分的水分传输效率和异速生长。在 eCO2 下生长导致所有物种的 gs 下降，但下降幅度差异很大，范围从 13%（颤杨）到 46%（美国皂荚）。伴随着 gs 的显著下降，植物水力结构发生了实质性变化，叶片面积和根系质量基础上的根水力导度总体显著下降，而茎和叶片水力效率要么增加，要么没有表现出一致的变化模式。此外，对 eCO2 的响应的异速生长的显著变化影响了整个植物的供水和需水关系。物种间 gs 响应的种间变异性与茎和叶水力导度的相对变化无关，但与根和叶之间的异速生长比例的相对变化密切相关，与物种的内在根系水力导度关系较小。研究结果强调，根和叶之间的异速生长调整在决定 gs 对 eCO2 的种间敏感性方面起着关键作用。植物水力及其相关的异速生长是 gs 对 eCO2 响应的重要变化，可能在介导叶片气体交换响应的种间变化方面发挥重要作用，这表明未来关于植物对 eCO2 响应的机制研究需要整合水力和异速生长的特征。
