Center for Ecological Research, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China; Key Laboratory of Sustainable Forest Ecosystem Management - Ministry of Education, Northeast Forestry University, Harbin 150040, China.
Center for Ecological Research, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China; Key Laboratory of Sustainable Forest Ecosystem Management - Ministry of Education, Northeast Forestry University, Harbin 150040, China.
Sci Total Environ. 2021 Mar 25;762:143077. doi: 10.1016/j.scitotenv.2020.143077. Epub 2020 Oct 17.
Defoliation resulting from herbivory, storm, drought, and frost may seriously impair tree growth and forest production. However, a comprehensive evaluation of defoliation impacts on tree carbon (C) assimilation and growth has not been conducted. We performed a meta-analysis of a dataset that included 1562 observations of 40 tree species from 50 studies worldwide, and evaluated defoliation impacts on photosynthetic capacity, C allocation, and tree growth. Our results showed that the reduced tree-level leaf area by defoliation outweighed the enhanced leaf-level photosynthesis, leading to a net reduction in tree C assimilation that was accompanied with decreases in nonstructural carbohydrates (NSCs) concentrations. The negative effects of defoliation on leaf NSCs decreased over time, but leaf production increased following defoliation, suggesting a shift in the C allocation towards shoots over roots. Defoliation intensity negatively affected tree growth, but post-defoliated recovery time did oppositely. The structure equation modelling showed that defoliation reduced tree growth mainly by indirectly reducing C assimilation (r = -0.4), and minorly by direct negative effect of defoliation intensity (r = -0.28) and positive effect of post-defoliated time (r = 0.33). These findings suggest that tree growth declines caused by defoliation are co-limited by C-source and sink activities, which provide a physiological basis of tree growth that is of significance in tree growth modelling and forest management under global changes.
由于食草、风暴、干旱和霜冻导致的落叶会严重损害树木的生长和森林的生产力。然而，对于落叶对树木碳（C）同化和生长的影响还没有进行全面的评估。我们对包括来自全球 50 项研究的 40 个树种的 1562 个观测数据的数据集进行了荟萃分析，并评估了落叶对光合作用能力、C 分配和树木生长的影响。我们的结果表明，落叶导致的树木层面叶片面积减少超过了增强的叶片层面光合作用，导致树木 C 同化的净减少，同时伴随着非结构性碳水化合物（NSC）浓度的降低。落叶对叶片 NSC 的负面影响随着时间的推移而减少，但落叶后叶片的产生增加，表明 C 分配向树枝而不是根部转移。落叶强度对树木生长有负面影响，但落叶后的恢复时间则相反。结构方程模型表明，落叶主要通过间接减少 C 同化（r=-0.4）来降低树木生长，其次是落叶强度的直接负效应（r=-0.28）和落叶后时间的正效应（r=0.33）。这些发现表明，落叶导致的树木生长下降受到 C 源和汇活动的共同限制，这为树木生长模型和全球变化下的森林管理提供了重要的生理基础。
