Abstract

Leaf ecophysiological traits are known to change with leaf and tree age. In the present study, we measured the effect of leaf and tree age on leaf ecophysiological and morphological traits of nitrogen-fixing Alnus nepalensis (D. Don) which is a pioneer tree species in degraded lands. Three naturally occurring A. nepalensis forest stands, namely young (5–8 years old), mature (40–55 years old), and old (130–145 years old), were considered in this study. We also investigated the seasonal variations in leaf ecophysiological and morphological traits during leaf flushing, fully expanded, and leaf senescence phenological stages. The ecophysiological and morphological traits were compared between leaf and tree ages using a linear mixed-effect model (LMM) and Tukey’s HSD test. Fully expanded leaves and young trees demonstrate ecophysiological traits consistent with acquisitive resource-use strategies. Our results revealed that net photosynthetic capacity (A_area and A_mass), leaf stomatal conductance (gsw_area and gsw_mass), transpiration rate (E_area and E_mass), specific leaf area (SLA), predawn and midday water potential (Ψ), leaf total chlorophyll concentration, photosynthetic N- and P-use efficiency (PNUE and PPUE) were higher in younger trees than mature and old trees. We found lower water-use efficiency (WUE) and intrinsic water-use efficiency (WUE_i) in young trees than in mature and old ones. Mass-based net photosynthetic capacity (A_mass) was positively correlated with PNUE, PPUE, transpiration rate, stomatal conductance, SLA and chlorophyll concentrations but negatively correlated with WUE and WUE_i. However, mass-based leaf nitrogen (N) and phosphorus (P) concentrations were the highest in fully expanded leaves and did not vary with tree age despite N concentration being negatively correlated with SLA. Overall, this study provides valuable insights into the age-related changes in leaf ecophysiological traits of A. nepalensis. The findings underscore the importance of considering tree age when studying plant ecophysiology and highlight the acquisitive resource-use strategies employed by young trees for rapid growth and establishment.

中文翻译：

---

喜马拉雅中部尼泊尔桤木叶和树龄相关的叶生态生理特征、养分和适应策略的变化

摘要

众所周知，叶子的生态生理特征会随着叶子和树龄的变化而变化。在本研究中，我们测量了叶子和树龄对退化土地上的先锋树种尼泊尔桤木(D. Don) 的叶子生态生理和形态特征的影响。本研究考虑了三种自然存在的尼泊尔云杉林分，即年轻林分（5-8岁）、成熟林分（40-55岁）和老年林分（130-145岁）。我们还研究了叶片冲洗、完全展开和叶片衰老物候阶段叶片生态生理和形态特征的季节变化。使用线性混合效应模型 (LMM) 和 Tukey 的 HSD 检验比较叶龄和树龄之间的生态生理和形态特征。完全展开的叶子和幼树表现出与获取资源利用策略一致的生态生理特征。我们的结果揭示了净光合能力（A_面积和 A_质量）、叶片气孔导度（gsw_面积和 gsw_质量）、蒸腾速率（E_面积和 E_质量）、比叶面积 (SLA)、黎明前和中午水势 (Ψ) ）、叶片总叶绿素浓度、光合氮和磷利用效率（PNUE 和 PPUE）在幼树中均高于成熟树和老树。我们发现幼树的水分利用效率（WUE）和内在水分利用效率（WUE _i）低于成熟树和老树。基于质量的净光合能力（A_质量）与PNUE、PPUE、蒸腾速率、气孔导度、SLA和叶绿素浓度呈正相关，但与WUE和WUE _i呈负相关。然而，基于质量的叶片氮 (N) 和磷 (P) 浓度在完全展开的叶片中最高，并且不随树龄变化，尽管氮浓度与 SLA 呈负相关。总体而言，这项研究为尼泊尔猕猴桃叶子生态生理特征与年龄相关的变化提供了有价值的见解。研究结果强调了在研究植物生态生理学时考虑树龄的重要性，并强调了幼树为快速生长和建立而采用的获取资源利用策略。