Salmon Yann, Lintunen Anna, Dayet Alexia, Chan Tommy, Dewar Roderick, Vesala Timo, Hölttä Teemu
Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland.
Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland.
New Phytol. 2020 May;226(3):690-703. doi: 10.1111/nph.16436. Epub 2020 Feb 20.
Photosynthetic rate is concurrently limited by stomatal limitations and nonstomatal limitations (NSLs). However, the controls on NSLs to photosynthesis and their coordination with stomatal control on different timescales remain poorly understood. According to a recent optimization hypothesis, NSLs depend on leaf osmotic or water status and are coordinated with stomatal control so as to maximize leaf photosynthesis. Drought and notching experiments were conducted on Pinus sylvestris, Picea abies, Betula Pendula and Populus tremula seedlings in glasshouse conditions to study the dependence of NSLs on leaf osmotic and water status, and their coordination with stomatal control, on timescales of minutes and weeks, to test the assumptions and predictions of the optimization hypothesis. Both NSLs and stomatal conductance followed power-law functions of leaf osmotic concentration and leaf water potential. Moreover, stomatal conductance was proportional to the square root of soil-to-leaf hydraulic conductance, as predicted by the optimization hypothesis. Though the detailed mechanisms underlying the dependence of NSLs on leaf osmotic or water status lie outside the scope of this study, our results support the hypothesis that NSLs and stomatal control are coordinated to maximize leaf photosynthesis and allow the effect of NSLs to be included in models of tree gas-exchange.
光合速率同时受到气孔限制和非气孔限制（NSLs）的制约。然而，不同时间尺度上非气孔限制对光合作用的调控及其与气孔控制的协同作用仍未得到充分理解。根据最近的优化假说，非气孔限制取决于叶片的渗透或水分状况，并与气孔控制协同作用，以实现叶片光合作用的最大化。在温室条件下，对樟子松、欧洲云杉、垂枝桦和欧洲山杨幼苗进行了干旱和刻痕实验，以研究非气孔限制对叶片渗透和水分状况的依赖性，以及它们在分钟和周时间尺度上与气孔控制的协同作用，从而检验优化假说的假设和预测。非气孔限制和气孔导度均遵循叶片渗透浓度和叶片水势的幂律函数。此外，正如优化假说所预测的，气孔导度与土壤到叶片的水力导度的平方根成正比。尽管本研究未涉及非气孔限制对叶片渗透或水分状况依赖性的详细机制，但我们的结果支持以下假说：非气孔限制和气孔控制协同作用以实现叶片光合作用的最大化，并允许将非气孔限制的影响纳入树木气体交换模型。
