Covariation in Plant Functional Traits and Soil Fertility within Two Species-Rich Forests

The distribution of plant species along environmental gradients is expected to be predictable based on organismal function. Plant functional trait research has shown that trait values generally vary predictably along broad-scale climatic and soil gradients. This work has also demonstrated that at any one point along these gradients there is a large amount of interspecific trait variation. The present research proposes that this variation may be explained by the local-scale sorting of traits along soil fertility and acidity axes. Specifically, we predicted that trait values associated with high resource acquisition and growth rates would be found on soils that are more fertile and less acidic. We tested the expected relationships at the species-level and quadrat-level (20×20 m) using two large forest plots in Panama and China that contain over 450 species combined. Predicted relationships between leaf area and wood density and soil fertility were supported in some instances, but the majority of the predicted relationships were rejected. Alternative resource axes, such as light gradients, therefore likely play a larger role in determining the interspecific variability in plant functional traits in the two forests studied.沿环境梯度分布的植物物种格局，本可依据生物功能特性实现预测。植物功能性状（plant functional trait）研究已证实，性状值通常会沿大尺度气候与土壤梯度呈现可预测的变化规律。此类研究同时表明，在上述梯度的任意位点，均存在大量的种间性状变异。本研究提出，该种间变异可通过沿土壤肥力与酸度轴的局域尺度性状筛选得到合理解释。具体而言，我们预测：与高资源获取能力及生长速率相关的性状值，将富集于肥力更高、酸度更低的土壤中。我们依托巴拿马与中国的两处大型森林样地（共包含超过450个物种），分别在物种水平与20×20米样方（quadrat）水平上对上述预期关系开展了检验。部分案例中，叶面积、木材密度与土壤肥力间的预期关系得到了验证，但绝大多数预期关系并未获得支持。因此，在本研究涉及的两处森林中，其他资源轴（如光照梯度）可能在调控植物功能性状的种间变异方面发挥了更为关键的作用。