The goal of elucidating the primary mechanisms constraining the assembly and distribution of biodiversity remains among the central unresolved challenges facing the field of ecology. Simulation studies and experimental manipulations have focused on how patterns in community assembly result from bivariate relationships along productivity or environmental gradients. However, the joint influence of multiple resource gradients on the distribution of species richness in natural communities remains under-studied. Using data from a large network of multi-scale vegetation plots across forests and woodlands of the southeastern US, we find significant evidence for the scale dependent, joint constraints of forest structure and soil resources on the distribution of vascular plant species richness. In addition to their significant partial effects on species richness, understory light levels and soil fertility positively interact, suggesting a trade-off between the two limiting resources with species richness peaking both in high-light, low-fertility conditions as well as low-light, high-fertility settings. This finding provides a novel perspective on the biodiversity-productivity relationship that suggests a transition in limiting resources from soil nutrients to light availability when enhanced productivity results in reduced light resources for subordinate individuals. Results likewise have meaningful implications for our understanding of scale dependent community assembly processes as size-asymmetric competition replaces environmental filtering as the primary assembly mechanism structuring temperate forest communities along an increasing soil fertility gradient.

中文翻译：

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树冠覆盖限制了美国东南部植物群落的肥力-多样性关系

阐明限制生物多样性聚集和分布的主要机制的目标仍然是生态学领域面临的主要未解决挑战之一。模拟研究和实验操作集中在社区组装模式如何由生产力或环境梯度的双变量关系产生。然而，多种资源梯度对自然群落物种丰富度分布的共同影响仍未得到充分研究。使用来自美国东南部森林和林地的大型多尺度植被地块网络的数据，我们发现了森林结构和土壤资源对维管植物物种丰富度分布的规模依赖性、联合约束的重要证据。除了对物种丰富度的显着部分影响外，林下光照水平和土壤肥力正相互作用，表明两种有限资源之间的权衡，物种丰富度在高光、低肥力条件和低光条件下均达到峰值, 高生育率设置。这一发现为生物多样性-生产力关系提供了一个新的视角，表明当生产力提高导致下属个体的光资源减少时，限制资源从土壤养分到光可用性的转变。