Warming effects on the flux of CH4 from peatland mesocosms are regulated by plant species composition: Richness and functional types.

Peatlands in northeast China are experiencing severe climate warming. Most studies on peatlands focus on the responses of CH4 dynamics to temperature. However, they rarely consider the synchronous changes in the composition of plant communities caused by the expansion of vascular plants. In this study, an experiment combined warming with the manipulation of plants to examine the concentrations of CH4 porewater and its fluxes in the mesocosm. We found that warming increased the concentration of CH4 and its fluxes relative to the control treatments, and it was strongly modulated by plant richness and functional types. The average CH4 fluxes in the warming and non-warming mesocosms varied from 72.10 to 119.44 and 97.95 to 194.43 mg m-2 h-1, respectively. Plant species richness significantly increased CH4 flux at the warming level of 3.2 °C (P < 0.01). The presence of vascular plants, such as Carex globularis and Vaccinium uliginosum, significantly increased the CH4 fluxes after warming had occurred. Our results suggest that the distinct response of CH4 to richness and species primarily stemmed from the direct or indirect effects of plant biomass and functional characteristics. Therefore, more consideration should be given to the diversity changes caused by vascular plant expansion when estimating CH4 flux in boreal peatland, especially in the context of future climate warming.