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 ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) (Vcmax), stomatal control (Cgs%), leaf dry mass per area 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, whereas 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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叶子功能性状随叶龄的变化：亚马逊树的叶子何时会降低其光合能力？

亚马逊流域的大多数叶功能性状研究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。当考虑叶龄时，通常认为它是不连续的，并且根据定性观察将叶分为年龄类别。在这里，我们量化了叶片功能性状的年龄依赖性变化，例如 1,5-二磷酸核酮糖羧化酶/加氧酶 (Rubisco) (Vcmax)、气孔控制 (Cgs%)、每面积和叶片的叶片干质量的最大羧化率九种自然生长的亚马逊热带树木的常量营养素浓度，具有不同的物候策略。叶龄通过每月一次的枝级叶人口普查来评估；我们还根据叶子人口统计中第一次包含以来经过的天数，而不是预定的年龄等级，对叶子的实足年龄进行了叶子性状测量。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，年轻、发育中的叶片显示出最低的平均光合能力，在 45 天时增加到最大值，然后随着年龄逐渐下降。物种和物候习性之间的成熟时间差异很大，从 8 ± 30 到 238 ± 30 天，Vcmax 的下降速度从 -0.003 到 -0.065 μmol CO2 m-2 s-1 day-1 不等。气孔控制在幼叶中显着增加，但在达到峰值后保持不变。基于质量的磷和钾浓度与叶龄呈负相关，而氮没有随时间变化。因此，生活策略、叶片养分浓度和物候类型的差异，而不仅仅是叶龄效应，可能是理解亚马逊森林观察到的光合作用季节性的重要因素。此外，在不同的树木群落中分配叶龄类别可能不是研究亚马逊碳吸收季节性的推荐方法，因为无法确认所有树木的 Vcmax 和叶龄之间的关系。因此，可能是了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，在不同的树木群落中分配叶龄类别可能不是研究亚马逊碳吸收季节性的推荐方法，因为无法确认所有树木的 Vcmax 和叶龄之间的关系。因此，可能是了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，在不同的树木群落中分配叶龄类别可能不是研究亚马逊碳吸收季节性的推荐方法，因为无法确认所有树木的 Vcmax 和叶龄之间的关系。