Most leaf functional trait studies in the Amazon basin do not consider ontogenetic variations (leaf age), which may influence ecosystem productivity throughout the year. When leaf age is taken into account, it is generally considered discontinuous, and leaves are classified into age categories based on qualitative observations. Here, we quantified age-dependent changes in leaf functional traits such as the maximum carboxylation rate of Rubisco (Vcmax), stomatal control (Cgs%), leaf dry mass per area (LMA) and leaf macronutrient concentrations for nine naturally growing Amazon tropical trees with variable phenological strategies. Leaf ages were assessed by monthly censuses of branch-level leaf demography; we also performed leaf trait measurements accounting for leaf chronological age based on days elapsed since the first inclusion in the leaf demography, not predetermined age classes. At the tree community scale, a nonlinear relationship between Vcmax and leaf age existed: young, developing leaves showed the lowest mean photosynthetic capacity, increasing to a maximum at 45 days and then decreasing gradually with age in both continuous and categorical age-group analyses. Maturation times among species and phenological habits differed substantially, from 8 ± 30 to 238 ± 30 days, and the rate of decline of Vcmax varied from -0.003 to -0.065 μmol CO2 m-2 s-1 day-1. Stomatal control increased significantly in young leaves but remained constant after peaking. Mass-based phosphorus and potassium concentrations displayed negative relationships with leaf age, while nitrogen did not vary temporally. Differences in life strategies, leaf nutrient concentrations, and phenological types, not the leaf age effect alone, may thus be important factors for understanding observed photosynthesis seasonality in Amazonian forests. Furthermore, assigning leaf age categories in diverse tree communities may not be the recommended method for studying carbon uptake seasonality in the Amazon, since the relationship between Vcmax and leaf age could not be confirmed for all trees.

中文翻译：

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叶片功能性状随叶片年龄的变化：叶片何时会降低亚马逊树木的光合能力？

亚马逊河流域的大多数叶片功能性状研究都没有考虑个体发育变异（叶龄），这可能会影响全年的生态系统生产力。考虑叶龄时，通常认为叶龄是不连续的，并且根据定性观察将叶分为年龄类别。在这里，我们量化了9种自然生长的亚马逊热带树木叶片功能性状的年龄相关变化，例如Rubisco的最大羧化率（Vcmax），气孔控制（Cgs％），单位面积的叶片干质量（LMA）和叶片宏观营养素浓度具有多种物候策略。叶龄通过每月一次的分支级叶人口统计普查来评估；我们还根据从叶子人口统计资料中首次包含入选日期起经过的天数（而不是预定的年龄类别）进行了说明叶子时间顺序的叶子性状测量。在树木群落尺度上，Vcmax与叶龄之间存在非线性关系：在连续和分类年龄组分析中，发育中的年轻叶片显示出最低的平均光合能力，在45天时增加至最大值，然后随着年龄的增长而逐渐降低。物种之间的成熟时间和物候习惯差异很大，从8±30天到238±30天，并且Vcmax的下降速率从-0.003到-0.065μmolCO2 m-2 s-1 day-1。幼叶的气孔控制显着增加，但在达到峰值后保持恒定。基于质量的磷和钾浓度与叶龄呈负相关，而氮在时间上没有变化。因此，生活策略，叶片养分浓度和物候类型（而不是单独的叶片年龄效应）的差异可能是理解亚马逊森林中观察到的光合作用季节性的重要因素。此外，在亚马逊地区研究碳吸收季节性的方法可能不建议在不同的树木群落中指定叶龄类别，因为无法确定所有树木的Vcmax与叶龄之间的关系。因此可能是了解亚马逊河森林中观察到的光合作用季节性的重要因素。此外，在亚马逊地区研究碳吸收季节性的方法可能不建议在不同的树木群落中指定叶龄类别，因为无法确定所有树木的Vcmax与叶龄之间的关系。因此可能是了解亚马逊河森林中观察到的光合作用季节性的重要因素。此外，在亚马逊地区研究碳吸收季节性的方法可能不建议在不同的树木群落中指定叶龄类别，因为无法确定所有树木的Vcmax与叶龄之间的关系。