CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; Key Laboratory of Terrestrial Ecosystem Carbon Neutrality, Liaoning Province, Shenyang 110016, China; Qingyuan Forest CERN, National Observation and Research Station, Liaoning Province, Shenyang 110016, China.
CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China; Key Laboratory of Terrestrial Ecosystem Carbon Neutrality, Liaoning Province, Shenyang 110016, China; Qingyuan Forest CERN, National Observation and Research Station, Liaoning Province, Shenyang 110016, China.
Sci Total Environ. 2023 Jan 15;856(Pt 1):159017. doi: 10.1016/j.scitotenv.2022.159017. Epub 2022 Sep 24.
Drought combined with extreme heatwaves has been increasingly identified as the important trigger of worldwide tree mortality in the context of climate change; nonetheless, our understanding of the potential hydraulic and thermal impairments of hot droughts to trees and the subsequent post-recovery process remains limited. To investigate the response of tree water and carbon relations to drought, heatwave, and combined drought-heatwave stresses, three-year-old potted seedlings of Fraxinus mandshurica Rupr., a dominant tree species in temperate forests of northeast China, were grown under well-watered and drought-stressed conditions and exposed to a rapid, acute heatwave treatment. During the heatwave treatment with a maximum temperature exceeding 40 °C for two days, the leaf temperature of drought-stressed seedlings was, on average, 5 °C higher than that of well-watered counterparts due to less effective evaporative cooling, indicating that soil water availability influenced leaf thermoregulatory capacity during hot extremes. Consistently, more pronounced crown damage, as shown by 13 % irreversible leaf scorch, was found in seedlings under the drought-heatwave treatment relative to sole heatwave treatment, alongside the more severe stem xylem embolism and leaf electrolyte leakage. While the heatwave treatment accelerated the depletion of non-structural carbohydrates in drought-stressed seedlings, the increase of branch soluble sugar concentration in response to heatwave might be related to the requirement for maintaining hydraulic functioning via osmoregulation under high dehydration risk. The coordination between leaf stomatal conductance and total non-structural carbohydrate content during the post-heatwave recovery phase implied that plant-water relations and carbon physiology were closely coupled in coping with hot droughts. This study highlights that, under scenarios of aggravating drought co-occurring with heatwaves, tree seedlings could face a high risk of crown decline in relation to the synergistically increased hydraulic and thermal impairments.
干旱与极端热浪相结合，已被越来越多地确定为气候变化背景下全球树木死亡的重要触发因素；然而，我们对于热干旱对树木的潜在水力和热力损伤以及随后的恢复过程的理解仍然有限。为了研究树木水分和碳关系对干旱、热浪和干旱-热浪复合胁迫的响应，我们对三年生盆栽水曲柳（Fraxinus mandshurica Rupr.）幼苗进行了研究，水曲柳是中国东北温带森林的优势树种。在充分供水和干旱胁迫条件下，将幼苗暴露于快速、急性热浪处理中。在持续两天、最高温度超过 40°C 的热浪处理中，由于蒸腾冷却效率较低，干旱胁迫幼苗的叶片温度平均比充分供水的对照高 5°C，表明土壤水分供应影响了极端高温下叶片的热调节能力。一致的是，与单独的热浪处理相比，干旱-热浪处理下的幼苗出现了更明显的树冠损伤，表现为 13%的不可逆叶片灼伤，同时还出现了更严重的茎木质部栓塞和叶片电解质渗漏。虽然热浪处理加速了干旱胁迫幼苗中非结构性碳水化合物的消耗，但在高脱水风险下通过渗透调节来维持水力功能的需求可能导致了响应热浪时枝条可溶性糖浓度的增加。在热浪后恢复阶段，叶片气孔导度与总非结构性碳水化合物含量之间的协调表明，在应对热干旱时，植物水分关系和碳生理密切相关。本研究强调，在干旱加剧与热浪同时发生的情况下，与水力和热力损伤协同增加相关，树幼苗可能面临树冠衰退的高风险。
