The distribution of nutrients, both vertically and horizontally in a forest, has long been theorized to influence primary productivity. Working at La Selva Biological Station, Costa Rica, we gathered the most comprehensive foliar samples to date for a lowland tropical rainforest to measure horizontal and vertical trends in foliar nutrients. The mean traits of foliage from forest floor to top-of-canopy were determined at 45 plots placed across the landscape in a stratified random design. Area-basis foliar N and P for these vertically integrated columns varied by a factor of 3, while foliar N:P and mass-basis foliar N and P varied by a factor of 2. The variance in plot-level foliar N:P and P was best explained by total soil P, while variance in foliar N was best explained by soil pH (regression trees: r² \(\ge \) 0.20, p \(\le \) 0.01). Other soil, topographic, and forest structure factors offered no additional explanatory power for variation of foliar nutrients from plot to plot. To explore vertical trends, we aggregated the data across the landscape into ~ 2 m vertical segments. We found that foliar N:P was unrelated to height in the canopy, and that area-basis foliar N and P increased with height in the canopy (linear regression: r² = 0.82 and r² = 0.65 respectively, p < 0.0001 for both). We compared these vertical trends to those of the eight other elements quantified in the leaves, and the only other element enriched with height was potassium (K). Vertical nutrient enrichment was driven by increases in leaf mass per area (LMA), not mass-basis concentrations. Altogether, these findings suggest that, even in diverse tropical rainforests, foliar chemistry may reflect environmental constraints.

从理论上讲，垂直和水平分布在森林中的养分分布都会影响初级生产力。在哥斯达黎加的La Selva生物站工作时，我们收集了迄今为止最全面的低地热带雨林的叶面样品，以测量叶面养分的水平和垂直趋势。从森林地面到树冠顶部的树叶的平均特征是通过分层随机设计在整个景观上放置的45个样地中确定的。这些垂直整合柱的面积基准叶面N和P变化系数为3，而叶面N：P和质量基面叶面N和P变化系数为2。 P最好用总土壤P来解释，而叶面N的变化最好用土壤pH来解释（回归树：r ² \（\ ge \） 0.20，p \（\ le \） 0.01）。其他土壤，地形和森林结构因素都无法为不同地块的叶面养分变化提供额外的解释力。为了探索垂直趋势，我们将整个景观中的数据汇总为约2 m的垂直段。我们发现叶冠层N：P与冠层的高度无关，而面积基准叶冠N和P随冠层的高度而增加（线性回归 分别为r ²  = 0.82和r ² = 0.65，p 两者均<0.0001）。我们将这些垂直趋势与叶片中定量的其他八种元素进行了比较，唯一富含高度的其他元素是钾（K）。垂直养分的富集是由单位面积叶片质量（LMA）而不是质量基准浓度的增加驱动的。总而言之，这些发现表明，即使在多样的热带雨林中，叶面化学物质也可能反映出环境限制。