Laughlin Daniel C, Lusk Christopher H, Bellingham Peter J, Burslem David F R P, Simpson Angela H, Kramer-Walter Kris R
Department of Botany University of Wyoming Laramie WY USA.
Environmental Research Institute School of Science University of Waikato Hamilton New Zealand.
Ecol Evol. 2017 Sep 21;7(21):8936-8949. doi: 10.1002/ece3.3447. eCollection 2017 Nov.
The worldwide plant economic spectrum hypothesis predicts that leaf, stem, and root traits are correlated across vascular plant species because carbon gain depends on leaves being adequately supplied with water and nutrients, and because construction of each organ involves a trade-off between performance and persistence. Despite its logical and intuitive appeal, this hypothesis has received mixed empirical support. If traits within species diverge in their responses to an environmental gradient, then interspecific trait correlations could be weakened when measured in natural ecosystems. To test this prediction, we measured relative growth rates (RGR) and seven functional traits that have been shown to be related to fluxes of water, nutrients, and carbon across 56 functionally diverse tree species on (1) juveniles in a controlled environment, (2) juveniles in forest understories, and (3) mature trees in forests. Leaf, stem, and fine root traits of juveniles grown in a controlled environment were closely correlated with each other, and with RGR. Remarkably, the seven leaf, stem, and fine root tissue traits spanned a single dimension of variation when measured in the controlled environment. Forest-grown juveniles expressed lower leaf mass per area, but higher wood and fine root tissue density, than greenhouse-grown juveniles. Traits and growth rates were decoupled in forest-grown juveniles and mature trees. Our results indicate that constraints exist on the covariation, not just the variation, among vegetative plant organs; however, divergent responses of traits within species to environmental gradients can mask interspecific trait correlations in natural environments. Correlations among organs and relationships between traits and RGR were strong when plants were compared in a standardized environment. Our results may reconcile the discrepancies seen among studies, by showing that if traits and growth rates of species are compared across varied environments, then the interorgan trait correlations observed in controlled conditions can weaken or disappear.
全球植物经济谱假说预测，维管植物物种的叶、茎和根性状相互关联，这是因为碳获取依赖于叶片获得充足的水分和养分供应，还因为每个器官的构建都涉及性能与持久性之间的权衡。尽管该假说在逻辑和直观层面颇具吸引力，但其实证支持参差不齐。如果物种内的性状对环境梯度的响应存在差异，那么在自然生态系统中进行测量时，种间性状相关性可能会被削弱。为了验证这一预测，我们测量了56种功能多样的树种的相对生长速率（RGR）以及七个已被证明与水分、养分和碳通量相关的功能性状，这些测量分别针对：（1）受控环境中的幼苗；（2）林下层的幼苗；（3）森林中的成年树。在受控环境中生长的幼苗的叶、茎和细根性状彼此密切相关，且与RGR相关。值得注意的是，在受控环境中测量时，七个叶、茎和细根组织性状跨越了单一的变异维度。与温室中生长的幼苗相比，在森林中生长的幼苗单位面积叶质量较低，但木材和细根组织密度较高。在森林中生长的幼苗和成年树中，性状与生长速率解耦。我们的结果表明植物营养器官之间的协变存在限制，而不仅仅是变异存在限制；然而，物种内性状对环境梯度的不同响应可能会掩盖自然环境中的种间性状相关性。当在标准化环境中比较植物时，器官之间的相关性以及性状与RGR之间的关系很强。我们的结果可能会调和不同研究之间的差异，表明如果在不同环境中比较物种的性状和生长速率，那么在受控条件下观察到的器官间性状相关性可能会减弱或消失。
