Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (N_tot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e. V_cmax, J_max) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25˚C (i.e. maximum rates of Rubisco carboxylation, V_cmax25 and of electron transport, J_max25) was higher in ES than in LS species (+ 58% and 68% for V_cmax25 and J_max25, respectively). While N_tot did not significantly differ between successional groups, the photosynthetic dependency on N_tot was markedly different. In ES species, V_cmax25 was strongly and positively related to N_tot but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25˚C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, R_d25 was positively related to N_tot for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic N_tot dependencies between species with different successional strategies.

当前，树种和树功能类型之间光合作用能力的差异主要是由叶片养分含量（尤其是氮（N））变化引起的。但是，最近的研究表明，叶片N含量通常不能很好地预测热带树木光合能力的变化。在这项研究中，我们探索了基于面积的总叶N含量（N _tot）和叶内N分配对光合能力与光收获在控制光合能力变化（即光收获）方面的相对重要性。V_的Cmax，Ĵ_最大）的12种，分属两种早期（ES）或晚演替（LS）组在卢旺达，中非热带山地雨林日益成熟的树木之中。普通叶片温度为25 leafC（即Rubisco羧化的最大速率，V_cmax25和电子传输，ĴES中的_max25）高于LS种（_max58和68％）V_cmax25和Ĵ_max25）。虽然连续组之间的N _tot没有显着差异，但是光合作用对N _tot的依赖性却明显不同。在ES物种中V_cmax25与N _tot呈正相关，但在LS物种中并非如此。但是，在叶片N的相对投资与使光合能力最大化的化合物与使光收成最大化的化合物之间没有重大的取舍。ES中的叶片暗呼吸在25˚C（+ 33％）以及更令人惊讶的是，表观的光合作用量子产率（+ 35％）高于LS物种。此外，对于ES和LS物种，R _d25与N _tot正相关。我们的结果表明，如果他们考虑将叶内氮分配与光合作用N _tot进行对比，则在量化热带山地雨林碳通量方面的工作将会得到改善。 具有不同演替策略的物种之间的依赖性。