Wetland methane emissions altered by vegetation disturbance: An interaction between stem clipping and nutrient enrichment

Abstract

Plant-mediated transport is the dominant means of methane release from vegetated wetlands. Whether aboveground plant disturbances affect the emission of methane is largely unknown. We tested the effects of stem clipping on methane emissions from freshwater wetland mesocosms vegetated with Sagittaria lancifolia, Panicum hemitomon, Echinochloa walteri, or Eleocharis macrostachya under different nutrient regimes. Mesocosms vegetated with E. macrostachya showed an effect of treatments on CH4 emission which was elevated in high nutrient level treatment and suppressed in mid nutrient level treatment as compared to controls when the plant was clipped to 3cm above water line. S. lancifolia and P. hemitomon showed a similar pattern, and E. walteri showed no response to treatments. Mean CH4 emission significantly differed between species, being up to 56% higher in mesocosms vegetated with P. hemitomon. Treatments where plants were clipped below the water line had low initial emission rates, but these increased after three days. Sediment samples were analyzed for patterns in the microbial functional genes mcrA (methanogens) and pmoA (methanotrophs), but no changes in microbial communities in response to treatments were observed. Changes in methane emissions due to plant disturbances in wetlands warrant further investigation, but this study demonstrates that the available nutrient pool must also be considered. Additionally, initial responses to treatments were observed, but these responses tended to dissipate after three days, emphasizing the importance of monitoring CH4 emissions over time rather than only observing initial responses. Our results suggest that nutrient enrichment alone can suppress CH4 emission, however interactions with plant disturbances can be of equal importance.