Species-specific effects of vascular plants on carbon turnover and methane emissions from wetlands

Species composition affects the carbon turnover and the formation and emission of the greenhouse gas methane (CH4) in wetlands. Here we investigate the individual effects of vascular plant species on the carbon cycling in a wetland ecosystem. We used a novel combination of laboratory methods and controlled environment facilities and studied three different vascular plant species (Eriophorum vaginatum, Carex rostrata and Juncus effusus) collected from the same wetland in southern Sweden. We found distinct differences in the functioning of these wetland sedges in terms of their effects on carbon dioxide (CO2) and CH4 fluxes, bubble emission of CH4, decomposition of C-14-labelled acetate into (CH4)-C-14 and (CO2)-C-14, rhizospheric oxidation of CH4 to CO2 and stimulation of methanogenesis through root exudation of substrate ( e. g., acetate). The results show that the emission of CH4 from peat - plant monoliths was highest when the vegetation was dominated by Carex (6.76 mg CH4 m(-2) h(-1)) than when it was dominated by Eriophorum (2.38 mg CH4 m(-2) h(-1)) or Juncus (2.68 mg CH4 m(-2) h(-1)). Furthermore, the CH4 emission seemed controlled primarily by the degree of rhizospheric CH4 oxidation which was between 20 and 40% for Carex but > 90% for both the other species. Our results point toward a direct and very important linkage between the plant species composition and the functioning of wetland ecosystems and indicate that changes in the species composition may alter important processes relating to controls of and interactions between greenhouse gas fluxes with significant implications for feedback mechanisms in a changing climate as a result.