Data from: Intraspecific variability and reaction norms of forest understory plant species traits

1.Trait-based models of ecological communities typically assume intraspecific variation in functional traits is not important, though such variation can change species trait rankings along gradients in resources and environmental conditions, and thus influence community structure and function. 2. We examined the degree of intraspecific relative to interspecific variation, and reaction norms of 11 functional traits for 57 forest understory plant species, including: intrinsic water-use efficiency (iWUE), Δ15N, 5 leaf traits, 2 stem traits and 2 root traits along gradients in light, nitrogen, moisture and understory cover. 3. Our results indicate that interspecific trait variation exceeded intraspecific variation by at least 50% for most, but not all traits. Intraspecific variation in Δ15N, iWUE, leaf nitrogen content and root traits was high (47-70%) compared with most leaf traits and stem traits (13-38%). 4. Δ15N varied primarily along gradients in abiotic conditions, while light and understory cover were relatively less important. iWUE was related primarily to light transmission, reflecting increases in photosynthesis relative to stomatal conductance. Leaf traits varied mainly as a function of light availability, with some reaction norms depending on understory cover. Plant height increased with understory cover, while stem specific density was related primarily to light. Resources, environmental conditions and understory cover did not contribute strongly to the observed variation in root traits. 5. Gradients in resources, environmental conditions and competition all appear to control intraspecific variability in most traits to some extent. However, our results suggest that species cross-over (i.e., trait rank reversals) along the gradients measured here are generally not a concern. 6. Intraspecific variability in understory plant species traits can be considerable. However, trait data collected under a narrow range of environmental conditions appears sufficient to establish species rankings and scale between community and ecosystem levels using trait-based models. Investigators may therefore focus on obtaining a sufficient sample size within a single set of conditions rather than characterizing trait variation across entire gradients in order to optimize sampling efforts.

1. 基于性状的生态群落模型通常假定功能性状的种内变异并不重要，尽管这类变异会改变物种沿资源与环境梯度的性状排名，进而影响群落结构与功能。
2. 我们针对57种森林林下植物的11项功能性状，检验了种间变异相对种内变异的程度，以及这些性状在光照、氮素、水分与林下盖度梯度下的反应规范；所涉性状包括：内在水分利用效率（intrinsic water-use efficiency, iWUE）、Δ15N、5项叶片性状、2项茎性状与2项根性状。
3. 研究结果显示，多数（但并非全部）性状的种间变异至少较种内变异高出50%。与多数叶片性状（13%~38%）和茎性状相比，Δ15N、iWUE、叶片氮含量以及根性状的种内变异占比更高（47%~70%）。
4. Δ15N的变异主要沿非生物环境梯度发生，光照与林下盖度的影响相对较弱。iWUE主要与光照透射率相关，这反映了相较于气孔导度的光合作用提升。叶片性状的变异主要取决于光照可获得性，部分反应规范受林下盖度调控。植物株高随林下盖度增加而升高，而茎比密度则主要与光照相关。资源、环境条件与林下盖度对观测到的根性状变异并无显著贡献。
5. 资源梯度、环境条件与种间竞争在一定程度上均调控了多数性状的种内变异。不过，本研究涉及的梯度下，物种性状交叉（即性状等级反转）通常并非需要关注的问题。
6. 林下植物功能性状的种内变异可以相当显著。不过，在狭窄环境条件范围内采集的性状数据，似乎足以用于建立物种性状排名，并利用基于性状的模型实现群落与生态系统尺度的尺度推绎。因此，研究者可聚焦于单一组环境条件下获取足够的样本量，而非为优化采样效率而表征全梯度下的性状变异。