Center for Ecological Research, Kyoto University, Otsu, Shiga, 520-2113, Japan.
Faculty of Agriculture, Kyoto University, Kyoto, Kyoto, 606-8502, Japan.
Sci Rep. 2017 Jun 7;7(1):2995. doi: 10.1038/s41598-017-03162-5.
Drought-induced tree die-off related to climate change is occurring worldwide and affects the carbon stocks and biodiversity in forest ecosystems. Hydraulic failure and carbon starvation are two commonly proposed mechanisms for drought-induced tree die-off. Here, we show that inhibited branchlet respiration and soil-to-leaf hydraulic conductance, likely caused by cell damage, occur prior to hydraulic failure (xylem embolism) and carbon starvation (exhaustion of stored carbon in sapwood) in a drought-tolerant woody species, Rhaphiolepis wrightiana Maxim. The ratio of the total leaf area to the twig sap area was used as a health indicator after drought damage. Six adult trees with different levels of tree health and one dead adult tree were selected. Two individuals having the worst and second worst health among the six live trees died three months after our study was conducted. Soil-to-leaf hydraulic conductance and leaf gas exchange rates decreased linearly as tree health declined, whereas xylem cavitation and total non-structural carbon remained unchanged in the branchlets except in the dead and most unhealthy trees. Respiration rates and the number of living cells in the sapwood decreased linearly as tree health declined. This study is the first report on the importance of dehydration tolerance and respiration maintenance in living cells.
干旱导致的树木死亡与气候变化有关，正在全球范围内发生，影响森林生态系统的碳储量和生物多样性。水力衰竭和碳饥饿是干旱导致树木死亡的两种常见机制。在这里，我们表明，在耐旱木本植物麻叶绣球中，与水力衰竭（木质部栓塞）和碳饥饿（边材中储存的碳耗尽）相关的侧枝呼吸和土壤到叶片水力传导率的抑制，可能是由细胞损伤引起的。在干旱损伤后，总叶面积与嫩枝液面积的比值被用作健康指标。选择了 6 棵具有不同树木健康水平的成年树木和一棵死亡的成年树木。在 6 棵活树中，健康状况最差和第二差的两个人在我们的研究进行三个月后死亡。土壤到叶片水力传导率和叶片气体交换速率随树木健康状况的下降呈线性下降，而木质部空化和总非结构性碳在嫩枝中除了死亡和最不健康的树木外保持不变。呼吸速率和边材活细胞数量随树木健康状况的下降呈线性下降。本研究首次报道了脱水耐性和活细胞呼吸维持的重要性。
