猫儿山交让木叶性状海拔变异格局及其环境影响因子

Altitudinal variation pattern in Daphniphyllum macropodum leaf traits and influencing environmental factors in Mao’er Mountain, China

分析相近树龄单一树种叶性状、叶性状网络的海拔变异格局及其影响因素,有助于排除遗传因素的影响,准确反映环境因子对叶片的作用规律。本研究对猫儿山海拔梯度上中龄林交让木叶片气孔性状、结构性状、化学性状和叶脉性状进行研究,分析了不同海拔(1100、1500和1900 m)叶性状和叶性状网络的变异格局、生活策略以及影响叶性状变异的主要环境因子。结果表明:交让木叶面积、比叶面积、叶厚、叶干物质含量、叶绿素含量、叶氮含量、叶磷含量、叶片C∶N、叶片C∶P、叶脉密度和叶脉直径在不同海拔间存在显著差异。年均温和总辐射分别解释叶性状42.1%和16.2%的变异,是驱动交让木叶性状海拔变异的关键环境因子。年均温对叶面积影响最大(R^(2)=0.73),总辐射对叶厚影响最大(R^(2)=0.72),均为显著正相关。1100 m低海拔交让木叶氮含量、叶磷含量较低,叶性状网络整体和内部均表现松散,采取资源保守型策略;1500 m中海拔交让木叶氮含量、叶磷含量较高,叶性状网络整体连接紧密局部松散,通过增强叶性状间的依赖性,显著提高磷利用效率,来应对落叶林分的竞争,采取资源获取型策略;1900 m高海拔交让木叶厚、叶干物质含量和叶绿素含量较大,叶面积较小,叶性状网络局部连接紧密而整体松散,体现了资源保守型策略。叶片C∶P-叶磷含量权衡关系与磷利用效率密切相关,其变化是辨识不同海拔交让木生活策略的重要指示。

Analyzing the pattern of altitudinal variation in the leaf traits and their networks of a particular tree species of similar age and its influencing factors could contribute to understanding the impacts of environmental factors on leaf traits and excluding the interference of genetic factors. We investigated the stomatal, structural, chemical, and vein traits of Daphniphyllum macropodum leaves in middle-aged forests, following the altitudinal gradient(1100, 1500, and 1900 m) on Mao'er Mountain. The objectives of this study were to reveal patterns in leaf trait and leaf trait networks variation, the life strategy of the tree species, and the major environmental factors affecting the altitudinal variations. The results showed that leaf area, specific leaf area, leaf thickness, leaf dry matter content, chlorophyll content, nitrogen content, phosphorus content, C:N, C:P, vein density, and vein diameter varied significantly across altitudes. Mean annual temperature and total radiation explained 42.1% and 16.2% of leaf-trait variation, respectively. They served as key environmental factors driving the altitudinal variation in leaf traits. Mean annual temperature exhibited the greatest influence on leaf area(R^(2)=0.73), and total radiation exerted the most prominent effect on leaf thickness(R^(2)=0.72). Both relationships were significantly positive. D. macropodum exhibited low leaf nitrogen and phosphorus at the low altitude of 1100 m, and the overall and local trait networks were loose, adopting a conservative resource strategy. At the medium altitude of 1500 m, leaf nutrient contents were relatively high. The overall network of leaf traits was tightly connected and local network was loose. By enhancing the dependency among leaf traits, and improving phosphorus utilization efficiency, D. macropodum could cope with competition in deciduous forests and adopt resource acquisition strategies. Further, at the highest altitude of 1900 m, D. macropodum had relatively large leaf thickness, chlorophyll content, and leaf dry matter content, but relatively small leaf area. The local network connections were tight while the overall network looseness, indicating a resource conserving strategy. The trade-off relationship between C:P and leaf phosphorus content was closely related to phosphorus use efficiency, and its variation was an important indicator for identifying life strategies of D. macropodum in different altitudes.