Department of Ecology and Evolutionary Biology, University of California Los Angeles, 621 Charles E. Young Drive South, Los Angeles, CA, 90095, USA.
School of Ecology and Environment, Inner Mongolia University, 235 University West Road, Hohhot, Inner Mongolia, 010021, China.
New Phytol. 2019 Jul;223(1):134-149. doi: 10.1111/nph.15779. Epub 2019 Apr 11.
Given increasing water deficits across numerous ecosystems world-wide, it is urgent to understand the sequence of failure of leaf function during dehydration. We assessed dehydration-induced losses of rehydration capacity and maximum quantum yield of the photosystem II (F /F ) in the leaves of 10 diverse angiosperm species, and tested when these occurred relative to turgor loss, declines of stomatal conductance g , and hydraulic conductance K , including xylem and outside xylem pathways for the same study plants. We resolved the sequences of relative water content and leaf water potential Ψ thresholds of functional impairment. On average, losses of leaf rehydration capacity occurred at dehydration beyond 50% declines of g , K and turgor loss point. Losses of F /F occurred after much stronger dehydration and were not recovered with leaf rehydration. Across species, tissue dehydration thresholds were intercorrelated, suggesting trait co-selection. Thresholds for each type of functional decline were much less variable across species in terms of relative water content than Ψ . The stomatal and leaf hydraulic systems show early functional declines before cell integrity is lost. Substantial damage to the photochemical apparatus occurs at extreme dehydration, after complete stomatal closure, and seems to be irreversible.
鉴于全球众多生态系统的水资源短缺日益严重，迫切需要了解叶片在脱水过程中功能丧失的顺序。我们评估了 10 种不同被子植物叶片在脱水过程中再水合能力和光合作用系统 II 最大量子产量（F/F）的丧失，并测试了这些丧失相对于膨压丧失、气孔导度（g）下降和水力导度（K）的发生时间，包括同一研究植物的木质部和木质部外途径。我们解决了相对含水量和叶片水势（Ψ）功能障碍阈值的先后顺序。平均而言，叶片再水合能力的丧失发生在 g、K 和膨压丧失点下降 50%以上的脱水之后。F/F 的丧失发生在更强的脱水之后，无法通过叶片再水合恢复。在物种间，组织脱水阈值相互关联，表明性状的共同选择。就相对含水量而言，每种功能下降类型的阈值在物种间的变化比 Ψ 小得多。在细胞完整性丧失之前，气孔和叶片水力系统就表现出早期的功能下降。在完全关闭气孔后，光化学仪器会受到严重破坏，而且似乎是不可逆转的。
