Light heterogeneity interacts with plant-induced soil heterogeneity to affect plant trait expression

Phenotypic plasticity, the expression of traits dependent on an individual’s environment, should increase the range of communities in which a plant can establish, potentially influencing community assembly. Plasticity may be induced by either the mean or variance in conditions; however, plant responses to variance in the environment remain largely unquantified. We conducted a greenhouse experiment in northeastern Ohio using two congeneric pairs of perennial species in a design that crossed two soil heterogeneity and two light heterogeneity treatments. Nested within the soil heterogeneity treatment were patches of congener and conspecific origin, which tests the effects of possible plant-soil feedbacks on trait expression. We used plant biomass to measure performance and root:shoot ratio and specific leaf area (SLA) to measure resource acquisition and allocation. Plant biomass responded to the origin of the soil, consistent with the literature demonstrating that plant-soil feedbacks influence plant performance. Soil and light heterogeneity interacted to significantly affect resource acquisition traits (i.e., SLA) demonstrating that plants integrated both above- and belowground resource variance. All four species showed light-dependent, non-additive effects of soil mixture, though these effects were only marginally significant (P < 0.10). This is important in the context of community assembly because studies find the variance in environmental drivers to be as, or more, important than the means in determining community structure. This study provides some of the first evidence that plant trait expression responds to the variance of environmental drivers, including those driven by plant-soil feedbacks, as well as the means.