Abstract
A common response of plant communities to increased nitrogen (N) deposition is a shift in species’ abundances. Multiple factors have been proposed to explain the changes in abundance, notably competition and soil acidification. We hypothesized that a plant species that decreased in abundance with elevated N would have lower ectomycorrhizal fungi, altered root‐associated bacteria communities, and/or greater susceptibility to Al toxicity than a species that increased in abundance with increasing N deposition. We examined changes in plant–microbe associations and Al toxicity in two dominant species from an alpine dry meadow community subjected to long‐term low‐level N addition. Carex rupestris has increased in cover over time with N addition and Kobresia myosuroideshas decreased. We conducted field sampling of soil microbes from treatment plots and tested whether field levels of Al have toxic effects on sedge species in a greenhouse study. Declines in ectomycorrhizal infection of Cenococcum geophilum occurred on Kobresia with increasing N treatment. In contrast, neither Al level nor changes in bacteria community composition corresponded with the change in cover of sedge species. Decreased ectomycorrhizal infection may have contributed to the decrease in abundance of Kobresia. This study contributes to an understanding of the types of plant–soil interactions that may influence how plant species respond to N deposition and rejects Al toxicity and changes in bacteria composition as factors that likely play a role in changes in sedge abundance.
