Data from: Species-specific responses of foliar nutrients to long-term nitrogen and phosphorus additions in a lowland tropical forest

1) The concentration, stoichiometry, and resorption of nitrogen (N) and phosphorus (P) in plant leaves are often used as proxies of the availability of these growth-limiting nutrients, but the responses of these metrics to changes in nutrient availability remains largely untested for tropical forest trees. 2) We evaluated changes in N and P concentrations, N:P ratios, and resorption for 4 common tree species after 13 years of factorial N and P additions in a lowland tropical forest in Panama. 3) Chronic P addition increased foliar P concentrations, decreased P resorption proficiency, and decreased N:P ratios in three locally common eudicot tree species (Alseis blackiana, Heisteria concinna, Tetragastris panamensis). The increase in foliar P involved similar proportional increases in organic and inorganic P in two species and a disproportionately large increase in inorganic P in A. blackiana. 4) Nitrogen addition did not alter foliar N concentrations in any species, but did decrease N resorption proficiency in H. concinna. 5) A fourth species, the palm Oenocarpus mapora, demonstrated remarkably static foliar nutrient concentrations, responding only with a marginal decrease in P resorption proficiency under N plus P co-addition. 6) Synthesis: Collectively, these results suggest that adjustment of N:P ratios can be expected in eudicots exposed to elevated P, but foliar N appears to already be at optimal levels in these lowland rainforest tree species. The complexity of species-specific responses to altered nutrient availability highlights the difficulty in predicting future responses of tropical forest trees to a changing world.1) 植物叶片的氮（N）、磷（P）浓度、化学计量比及养分重吸收（nutrient resorption）常被用作这类限制生长养分的可利用性的替代指标，但针对热带林木的这些指标对养分可利用性变化的响应，目前仍未得到充分验证。 2) 本研究针对巴拿马低地热带森林中的4种常见林木，在开展13年的氮、磷双因子添加实验后，评估了其叶片氮、磷浓度、氮磷比及养分重吸收的变化。 3) 长期磷添加可提升3种本土常见真双子叶植物（eudicot）Alseis blackiana、Heisteria concinna、Tetragastris panamensis的叶片磷浓度，降低其磷重吸收完全度，并缩小其氮磷比。其中两种物种的叶片磷含量提升同时伴随有机磷与无机磷的同等比例增长，而A. blackiana的无机磷增幅则显著高于有机磷。 4) 氮添加未改变任何受试物种的叶片氮浓度，但可降低Heisteria concinna的氮重吸收完全度。 5) 第4种受试物种为棕榈科的Oenocarpus mapora，其叶片养分浓度表现出显著的稳定性，仅在氮磷共添加处理下出现磷重吸收完全度的小幅下降。 6) 综合分析：整体而言，上述结果表明暴露于高磷环境的真双子叶植物的氮磷比可发生适应性调整，但这些低地雨林林木的叶片氮浓度似乎已处于最优水平。不同物种对养分可利用性变化的响应存在显著特异性，这凸显了预测热带林木未来对全球变化响应的难度。