College of Life and Environmental Sciences, Central South University of Forestry and Technology, Changsha, Hunan 410004, China; Huitong National Station for Scientific Observation and Research of Chinese Fir Plantation Ecosystems in Hunan Province, Huitong, Hunan 438107, China.
Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.
Sci Total Environ. 2024 Dec 10;955:177030. doi: 10.1016/j.scitotenv.2024.177030. Epub 2024 Oct 21.
Transpiration is a key process that couples the land-atmosphere exchange of water and carbon, and its maximum water transport ability affects plant productivity. Functional traits significantly influence the maximum transpiration rate; however, which factor plays the dominant role remains unknown. SAPFLUXNET dataset, which includes sap flux density of diverse species worldwide, provides fundamental data to test the importance of photosynthetic and hydraulic traits on maximum tree-level sap flux density (J). Here, we investigated variations in J of 2194 trees across 129 species using data from the SAPFLUXNET dataset, and analysed the relationship of J with photosynthetic and hydraulic traits. Our results indicated that J was positively correlated with photosynthetic traits at both leaf and tree level. Regarding hydraulic traits, J was positively related to xylem hydraulic conductivity (K), leaf-specific hydraulic conductivity (K), xylem pressure inducing 50 % loss of hydraulic conductivity (P), xylem vessel diameter (V), and leaf-to-sapwood area ratio (AA). Random forest model showed that 87 % of the variability in J can be explained by functional traits, and hydraulic traits (e.g., P and sapwood area, A) exerted larger effects on J than photosynthetic traits. Moreover, trees with a lower sapwood area or depth could increase their sap flux density to compensate for the reduced whole-tree transpiration. J of the angiosperms was significantly higher than that of the gymnosperms. Mean annual total precipitation (MAP) were positively related to J with a weak correlation coefficient. Furthermore, J showed a significant phylogenetic signal with Blomberg's K below 0.2. Overall, tree species with acquisitive resource economics or more efficient hydraulic systems show higher water transport capacity, and the efficiency of xylem hydraulic system rather than the demand for carbon uptake predominantly determines water transport capacity.
蒸腾作用是连接陆地-大气间水分和碳交换的关键过程，其最大水分运输能力影响植物生产力。功能性状显著影响最大蒸腾速率；然而，哪种因素起主导作用尚不清楚。SAPFLUXNET 数据集包含了全球多种物种的 sap 通量密度，为测试光合和水力性状对最大树木级 sap 通量密度（J）的重要性提供了基础数据。在这里，我们利用 SAPFLUXNET 数据集的数据，研究了 129 个物种的 2194 棵树木的 J 变化，并分析了 J 与光合和水力性状的关系。我们的结果表明，J 与叶片和树木水平的光合性状呈正相关。就水力性状而言，J 与木质部导水率（K）、叶片比导水率（K）、木质部压力诱导 50%导水率丧失（P）、木质部导管直径（V）和叶-木质部面积比（AA）呈正相关。随机森林模型表明，J 的 87%的变异性可以用功能性状来解释，水力性状（如 P 和木质部面积 A）对 J 的影响大于光合性状。此外，具有较低木质部面积或深度的树木可以增加 sap 通量密度来补偿整个树木蒸腾作用的减少。被子植物的 J 明显高于裸子植物。年平均总降水量（MAP）与 J 呈正相关，相关系数较弱。此外，J 表现出明显的系统发育信号，Blomberg 的 K 值低于 0.2。总体而言，具有资源获取经济或更高效水力系统的树种具有更高的水分运输能力，木质部水力系统的效率而不是对碳吸收的需求决定了水分运输能力。
