Differential stoichiometric homeostasis and growth in two native and two invasive C₃ grasses

Global changes interact with plant invasions by differentially impacting native and invasive species. For example, invasive plants often benefit from eutrophication to a greater degree than native plants. While this is well-documented, a broad, trait-based explanation for this phenomenon is lacking. Recent research shows that stoichiometric homeostasis predicts plant species responses to eutrophication and drought, but this research has not been extended into an invasion ecology paradigm. We tested the hypotheses that stoichiometric homeostasis would differ between native and invasive plants, that expressed levels of stoichiometric homeostasis would respond to water availability, and that differences in stoichiometric homeostasis would match differences in growth. In a nutrient and water manipulation study, we found that stoichiometric homeostasis differed between native grasses (Elymus canadensis and Pascopyrum smithii) and invasive grasses (Agropyron cristatum and Bromus inermis), that differences in stoichiometric homeostasis matched differences in growth in well-watered grasses, and that expressed levels of stoichiometric homeostasis were stable across the water supply treatments. These results suggest that invasive plants maintain growth advantages over native plants in eutrophic conditions because of differential homeostatic requirements. We argue that stoichiometric homeostasis is therefore a useful functional trait to explain and predict differential native and invasive plant responses to global change.