Nutrient supply alters goldenrod’s induced response to herbivory

Recent interest in using trait-based approaches to understand and predict ecosystem processes and evolutionary responses to environmental change (both biotic and abiotic), highlights the need to understand the relative importance of genetic and environmental sources of intraspecific trait variation within local populations of dominant species. Here, I combine plant defense theory with functional approaches to quantify genetic trait variation and phenotypic trait plasticity of nine goldenrod (Solidago altissima) genotypes derived from a local field population in Connecticut, USA to herbivory along a nutrient supply gradient. I found that increasing nutrient supply changed the dominant plant defense strategy from tolerance to induced resistance. Induced resistance was detected through decreased herbivore growth rates and a behavioral feeding shift of grasshoppers to older leaf tissue. This could not be fully accounted for through stoichiometric changes in leaf tissue quality. A multi-dimensional phenotype approach revealed that abiotic and biotic environments (nutrients and herbivory) accounted for almost as much whole-plant trait variation (31%) as did plant genotype (36%). Increasing nutrient supply and herbivory resulted in independent and differential effects on whole-plant trait expression. Increasing both treatments concurrently produced a unique plant phenotype with increased leaf carbon content and allocation to asexual reproduction (ExE). Notably, individual genotypes exhibited different magnitudes of multivariate trait plasticity to nutrient and herbivory gradients. However, the population of genotypes as a whole within a given environment expressed an approximately equal magnitude of trait variation across both permissive (high nutrient, no herbivory) and stressful (low nutrient, high herbivory) environments. Quantifying plasticity in defensive strategy in concert with correlated whole-plant trait expression changes across multiple abiotic and biotic factors may be key to providing a mechanistic understanding of how heterogeneous landscapes impact community interactions and ecosystem processes.

近年来，学界对利用基于性状的研究方法（trait-based approaches）理解并预测生态系统过程，以及解析生物与非生物环境变化下的进化响应的兴趣日益浓厚，这凸显了厘清优势物种本地种群内种内性状变异（intraspecific trait variation）的遗传与环境来源相对重要性的迫切需求。本研究将植物防御理论（plant defense theory）与功能性状研究方法相结合，针对采自美国康涅狄格州某本地田间种群的9株高一枝黄花（Solidago altissima）基因型，量化其在养分供应梯度下面对植食作用时的遗传性状变异与表型性状可塑性（phenotypic trait plasticity）。本研究发现，养分供应水平提升会将优势植物的防御策略从耐性（tolerance）转变为诱导抗性（induced resistance）。诱导抗性可通过植食者生长速率下降以及蝗虫的取食行为转向老叶组织得以观测到。该现象无法仅通过叶组织质量的化学计量变化（stoichiometric changes）得到完全解释。多维表型研究方法（multi-dimensional phenotype approach）结果显示，非生物与生物环境（养分与植食作用）对全株性状变异的解释度（31%）与植物基因型（36%）几乎相当。提升养分供应与施加植食作用，对全株性状表达的影响相互独立且存在差异。同时提升两种处理因素的水平，会产生一种独特的植株表型：叶片碳含量升高且无性繁殖（asexual reproduction）的资源分配增加（即ExE处理组）。值得注意的是，不同基因型对养分与植食作用梯度的多变量性状可塑性（multivariate trait plasticity）幅度存在差异。然而，在特定环境下，该基因型种群整体在适宜环境（高养分、无植食作用）与胁迫环境（低养分、高植食作用）中展现出的性状变异幅度大致相当。综合量化防御策略的可塑性，以及跨多种非生物与生物因素的全株性状关联表达变化，或是从机制层面理解异质景观如何影响群落互作（community interactions）与生态系统过程（ecosystem processes）的关键所在。