Invasive woody shrubs often exhibit higher assimilation rates and faster growth compared to neighboring native shrubs. One underexplored explanation for this difference in growth strategy involves belowground interactions with microorganisms in the invaded range. These plants are associated with mutualistic arbuscular mycorrhizal fungi that are involved in resource uptake, but the extent to which nativity and environmental factors determine the degree of association remains unknown. We asked how native and nonnative, invasive species differ in their allocation to above and belowground biomass in the context of mycorrhizal and nutrient status. We also investigated belowground functional traits (root length, root diameter, specific root length of absorptive roots, branching intensity, root tip density and percent colonization) to determine whether mycorrhizal status and nutrient regime affect growth strategy differences and plasticity within traits. Using softwood cuttings from a common garden in Syracuse, NY, we grew 20 species of native and nonnative shrubs in mycorrhizal and nonmycorrhizal conditions under high and low nutrient regimes. Plants were harvested and measured after 4 months, and the intact root systems were analyzed for differences in root functional traits.
Results/Conclusions
Across invasive species there was a difference in the biomass of mycorrhizal and nonmycorrhizal treatments, but only under low nutrients. For native species we found the mycorrhizal treatment difference significant under both nutrient regimes. Accordingly, mycorrhizal growth response—measured as the difference between mycorrhizal and nonmycorrhizal plant biomass—exhibited a difference in all treatments except invasive shrubs under high nutrients. Root biomass was lower across all mycorrhizal plants except invaders at high nutrient levels. This suggests there is little difference between mycorrhizal and nonmycorrhizal invasive shrub productivity at high nutrients, which could be due to the more highly facultative response of these invaders to the formation of mycorrhizae under favorable conditions. Consistent with this, mycorrhizal status affected branching intensity, root tip density and primary root length across native species, while invaders exhibited mycorrhizal-induced trait plasticity only at low nutrient levels. Our results suggest that native and nonnative shrubs differ in their belowground strategies, including allocation to roots and associated fungal mutualists, which may help us better understand how plant resource strategy translates to belowground contexts.