Non-native, invasive woody shrubs often exhibit higher assimilation rates and faster growth compared to neighboring native shrubs. One underexplored explanation for this difference in growth involves belowground interactions with microorganisms in the invaded range. Although invaders are known to associate with mutualistic arbuscular mycorrhizal fungi (AMF) that are involved in resource uptake, the nature of this interaction and its environmental dependence remains unknown. We asked how native and non-native species differ in growth in the context of mycorrhizal and nutrient status. We also explored whether species’ mycorrhizal growth response (MGR) is predictable from traits related to the leaf economic spectrum (LES). Using softwood cuttings from a common garden in Syracuse, NY, we grew 12 species of native and non-native shrubs in mycorrhizal and nonmycorrhizal conditions under high and low nutrient regimes. In a hierarchical Bayesian model, we tested whether MGR differed systematically for native and non-native species, and whether these responses depended on nutrient regime and LES species’ traits (leaf lifespan, photosynthetic rate, leaf extension rate and leaf nitrogen concentration).
Results/Conclusions
Mycorrhizal treatment, nativity, and nutrient regime were all shown to be important predictors of plant growth. Moreover, the interaction between nativity and AMF was also important, with native shrubs showing a greater growth in response to AMF colonization. Native and non-native species fell equally across the trait derived LES illustrating that nativity effects were not driven by differences in LES traits across groups. MGR was correlated with the LES (i.e. more “acquisitive” species experienced greater MGR), but only under low nutrient conditions. While our study shows that native shrubs gain the most from AMF colonization, non-native species exhibited greater biomass than natives across all treatments. Greater nonmycorrhizal growth may allow more facultative non-natives to thrive under certain conditions such as high disturbance. Root-shoot ratios were found to be greatest under treatments resulting in lower total biomass, indicating a tradeoff driven by mycorrhizas, nutrients and an AMF-nativity interaction. Thus, despite a greater growth response of native species to AMF colonization, our results help explain why nonnatives have greater capacity for competitive growth across an array of environments.