Woody invaders do not alter rhizosphere microbial activity in a temperate deciduous forest

Abstract

Non-native, invasive plants are often strong competitors that have large effects on ecosystem functioning. While limited experimental evidence suggests invasive species can change soil carbon (C) and nitrogen (N) processes, little is known about how they alter biogeochemistry in the field. We examined soils collected from beneath native and non-native, invasive woody plants in a temperate forest in central New York, USA, to test whether invaders change rhizospheric C and N processes compared to that of common native species. We hypothesized that a combination of high-quality leaf and root litter and greater rates of rhizospheric deposition of invaders would enhance the quality of soil organic matter, leading to greater measured rates of C and N mineralization. We removed soil cores from directly below the canopy of 105 individuals of 8 native and 3 invasive species of shrubs and small trees, each paired with an adjacent sample to account for site effects on soil properties. We measured inorganic N pools, percent soil C and N, and potential C and N mineralization rates with 10-day laboratory incubations. Contrary to our hypothesis, we found that invaders did not significantly alter any of the measured soil traits. Instead, root biomass per sample, which did not vary by nativity, was a better predictor of potential mineralized C and N. This suggests plant tissue quantity controls available C and N pools, and plants that produce more roots are able to better stimulate microbial activity. Thus, understory invaders do not appear to alter soil biogeochemistry in this forest unless they drive large changes in forest root mass.