珍稀濒危树种坡垒不同径级个体枝叶性状的变异性研究

Variation in branch and leaf traits among different diameter classes of the rare and endangered tree species Hopea hainanensis

关键词:  木质部组织，水分运输，叶片厚度，机械抗性，种内变异

Key words:  xylem tissue, water transport, leaf thickness, mechanical resistance, intraspecific variation

摘要:

坡垒(Hopea hainanensis)是国家一级保护植物，了解该种不同生长阶段的适应策略对制定迁地保护措施至关重要。枝叶功能性状及其种内变异被广泛地用于分析植物的环境适应性，但是关于坡垒的功能性状的相关研究较少。为探究坡垒不同径级枝叶结构的适应性，该研究选择不同时期种植在海南兴隆热带花园的坡垒个体(胸径范围1~17 cm)，测定其冠层枝条木质部结构性状(导管腔比例、导管壁厚度、薄壁组织比例、木射线组织比例、纤维组织比例、导管密度、导管壁加固系数)、水力性状(水力导管直径、理论导水率)、叶片形态解剖特征(叶片各组织厚度、比叶面积)以及机械抗性，采用Pearson相关性分析和主成分分析探讨性状与径级之间以及枝叶性状之间的相关关系。结果表明：(1)随着径级增大，单位枝条木质部横切面的导管腔和导管壁比例以及木质部薄壁组织比例、水力导管直径、理论导水率均显著增加，而纤维组织比例、导管密度、导管壁加固系数显著降低。 (2)叶片各组织(表皮、角质层、叶肉组织)厚度和机械抗性随着径级的增大而显著增加。(3)在个体水平上，枝条木质部水分运输能力与叶片厚度呈显著正相关。综上所述，坡垒大径级个体通过调整枝条木质部结构以增强水分运输能力，同时增加叶片厚度减少蒸腾耗水，枝叶结构的协同有利于维持水分平衡。该研究结果揭示了坡垒个体冠层枝叶结构随着径级增大(蒸腾需水、光照强度以及水汽压亏缺增加)的适应性变化规律，可为该种的保护与栽培管理提供参考。

Abstract:

Hopea hainanensis is a national first-class protected plant species in China. Understanding its adaptive strategies across different growth stages is critical for formulating effective ex situ conservation measures. Functional traits of branches and leaves and their intraspecific variation are widely used to analyze plants’ environmental adaptability. However, research on the functional traits of H. hainanensis remains scarce. To investigate the adaptability of branch and leaf structures at different diameter classes in?H. hainanensis, in this study, we selected individuals planted at different times in the Xinglong Tropical Garden, Hainan, China, with stem diameter at breast height (DBH ranged from 1-17 cm), and measured canopy branch xylem structural traits (vessel lumen proportion, vessel wall proportion, axial parenchyma proportion, ray parenchyma proportion, fiber proportion, vessel density, vessel wall reinforcement index), hydraulic traits (hydraulic vessel diameter, theoretical hydraulic conductivity), leaf morphological and anatomical traits (thickness of leaf tissues and specific leaf area), and mechanical resistance. Pearson correlation analysis and principal component analysis were used to explore the correlation between traits and diameter classes, as well as among branch and leaf traits. The results were as follows：(1) As the DBH increased, the proportion of vessel lumen and wall, and parenchyma cell per branch xylem cross-section area, hydraulically-weighted vessel diameter, and theoretical hydraulic conductivity significantly increased, while the fiber tissue proportion, vessel density, and vessel wall reinforcement coefficient significantly decreased. (2) The thickness of individual leaf tissues (epidermis, cuticle, and mesophyll) and the mechanical resistance of the leaf blade increased significantly with DBH. (3) At the individual level, the branch hydraulic efficiency was positively correlated with leaf tissue thickness. In conclusion, large diameter individuals of H. hainanensis enhance their xylem hydraulic capacity by adjusting branch xylem structure, while increaing leaf thickness to reduce transpirational water loss. The structural coordination between branch and leaf could maintain water balance. The results reveal the adaptive adjustment of branch and leaf structure with increasing DBH (corresponding to increasing transpirational water demand, light intensity, and vapor pressure deficit) in H. hainanensis, thus offering valuable implications for the species’ conservation and cultivation.