Martin-StPaul Nicolas K, Limousin Jean-Marc, Rodr Guez-Calcerrada Jes S, Ruffault Julien, Rambal Serge, Letts Matthew G, Misson Laurent
Equipe DREAM, CEFE CNRS 1919 route de Mende 34000 Montpellier, France.
Department of Biology, University of New Mexico, MSC03 2020, Albuquerque, NM 87131-0001, USA.
Funct Plant Biol. 2012 Feb;39(1):25-37. doi: 10.1071/FP11090.
Drought frequency and intensity are expected to increase in the Mediterranean as a consequence of global climate change. To understand how photosynthetic capacity responds to long-term water stress, we measured seasonal patterns of stomatal (SL), mesophyll (MCL) and biochemical limitations (BL) to net photosynthesis (Amax) in three Quercus ilex (L.) populations from sites differing in annual rainfall. In the absence of water stress, stomatal conductance (gs), maximum carboxylation capacity (Vcmax), photosynthetic electron transport rate (Jmax) and Amax were similar among populations. However, as leaf predawn water potential (Ψl,pd) declined, the population from the wettest site showed steeper declines in gs, Vcmax, Jmax and Amax than those from the drier sites. Consequently, SL, MCL and BL increased most steeply in response to decreasing Ψl,pd in the population from the wettest site. The higher sensitivity of Amax to drought was primarily the result of stronger stomatal regulation of water loss. Among-population differences were not observed when gs was used instead of Ψl,pd as a drought stress indicator. Given that higher growth rates, stature and leaf area index were observed at the wettest site, we speculate that hydraulic architecture may explain the greater drought sensitivity of this population. Collectively, these results highlight the importance of considering among-population differences in photosynthetic responses to seasonal drought in large scale process-based models of forest ecosystem function.
由于全球气候变化，预计地中海地区干旱的频率和强度将会增加。为了解光合能力如何响应长期水分胁迫，我们测量了来自年降雨量不同地点的三个冬青栎种群中气孔（SL）、叶肉（MCL）和生化限制（BL）对净光合速率（Amax）的季节变化模式。在没有水分胁迫的情况下，种群间的气孔导度（gs）、最大羧化能力（Vcmax）、光合电子传递速率（Jmax）和Amax相似。然而，随着叶片黎明前水势（Ψl,pd）下降，来自最湿润地点的种群的gs、Vcmax、Jmax和Amax的下降幅度比来自较干燥地点的种群更陡。因此，在来自最湿润地点的种群中，SL、MCL和BL随着Ψl,pd的降低而增加得最为急剧。Amax对干旱的较高敏感性主要是由于对水分损失的气孔调节更强。当使用gs而非Ψl,pd作为干旱胁迫指标时，未观察到种群间差异。鉴于在最湿润地点观察到更高的生长速率、树高和叶面积指数，我们推测水力结构可能解释了该种群对干旱的更高敏感性。总体而言，这些结果突出了在基于过程的森林生态系统功能大规模模型中考虑种群间光合对季节性干旱响应差异的重要性。
