Although chemical deterrents to herbivory often exact costs in terms of plant growth, the manner in which those costs arise, and their physiological relationship to other functional traits, remain unclear. In the absence of appreciable herbivory, we examined interrelationships among chemical defense levels and other foliar functional traits (e.g., light-saturated photosynthesis, specific leaf area, nitrogen concentration) as co-determinants of tree growth and, by extension, competitive ability in high-density populations comprising 16 genotypes of Populus tremuloides. Across genotypes, concentrations of chemical defenses were not significantly related to other leaf functional traits, but levels of the salicinoid phenolic glycosides (SPGs) salicin, salicortin and tremulacin were each negatively correlated with relative mass growth (RMG) of aboveground woody tissue (P ≤ 0.001). RMG, in turn, underpinned 77% of the genotypic variation in relative height growth (our index of competitive ability). RMG was also positively related to light-saturated photosynthesis (P ≤ 0.001), which, together with the three SPGs, explained 86% of genotypic RMG variation (P ≤ 0.001). Moreover, results of a carbon balance simulation indicated that costs of resource allocation to SPGs, reaching nearly a third of annual crown photosynthesis, were likely mediated by substantial metabolic turnover, particularly for salicin. The lack of discernible links between foliar defense allocation and other (measured) functional traits, and the illustrated potential of metabolic turnover to reconcile influences of SPG allocation on RMG, shed additional light on fundamental physiological mechanisms underlying evolutionary tradeoffs between chemical defense investment and competitive ability in a foundation tree species.

中文翻译：

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竞争或防御：将功能性状变异与基础树种的生活史权衡联系起来。

尽管化学制止草食的方法通常会在植物生长方面确定确切的成本，但这些成本的产生方式及其与其他功能性状的生理关系尚不清楚。在没有明显的草食动物的情况下，我们研究了化学防御水平与其他叶片功能性状（例如光饱和的光合作用，比叶面积，氮浓度）之间的相互关系，这些相互关系决定了树木的生长，进而扩展了高树种的竞争能力密度种群，其中包括16个基因型的胡杨。在所有基因型中，化学防御作用的浓度与其他叶片功能性状没有显着相关，但水杨素酚醛糖苷（SPG）水杨素的水平 水杨素和海藻糖蛋白均与地上木质组织的相对质量增长（RMG）呈负相关（P≤0.001）。反过来，RMG支持相对身高增长（我们的竞争能力指数）的基因型变异的77％。RMG与光饱和光合作用也呈正相关（P≤0.001），该光合作用与三个SPG一起解释了86％的基因型RMG变化（P≤0.001）。此外，碳平衡模拟的结果表明，达到SPG的资源分配成本（几乎达到年度冠状光合作用的三分之一）可能是由大量的代谢周转所介导的，尤其是水杨素。叶面防御分配与其他（可衡量的）功能性状之间缺乏可辨别的联系，