Altered ecosystem carbon and nitrogen cycles by plant invasion: A meta-analysis

A comprehensive evaluation of responses of carbon (C) and nitrogen (N) cycles to plant invasion is urgently needed to understand the impacts of biological invasion on ecosystem biogeochemical cycles. This study synthesized 105 experimental studies to quantify the extent to which C and N cycles respond to plant invasion using meta-analysis. Nineteen variables related to C and N cycles were examined in invaded and native ecosystems. These variables included C and N stocks in shoots, roots, and soils, C stock in litter, root:shoot ratio in biomass, soil C:N ratio, litter C:N ratio, aboveground net primary production (ANPP), litter decomposition, soil net N mineralization and nitrification, plant N concentration, litter N and lignin concentrations, and soil NH₄⁺ and NO₃^- concentrations. Our results showed that C and N stocks in plants and soils all significantly increased in invaded ecosystems relative to native ecosystems, ranging from a 4% increase in soil C stock to a 110% increase in shoot C stock. Root:shoot ratio in biomass, litter and soil C:N ratios were lower by 14, 20, and 5%, respectively, in invaded than native ecosystems. ANPP, rate of litter decomposition, rates of soil net N mineralization and nitrification increased on average by 41, 63, 43, and 91% respectively, in invaded ecosystems in comparison with native ecosystems. Plant N concentration, litter N and lignin concentrations, soil NH₄⁺ and NO₃^- concentrations were higher in invaded ecosystems by 43, 25, 8, 12 and 49%, respectively, than native ecosystems. Invasion by woody species usually generated larger impacts on C and N cycles than by herbaceous species. Invaded forests, grasslands, and wetlands did not show much differential response to plant invasion. All of these changes suggest that plant invasion profoundly alters ecosystem biogeochemical cycles.