Spatial and Temporal Variability and Driving Factors of Carbon Dioxide and Nitrous Oxide Fluxes in Alpine Wetland Ecosystems

Plants regulate greenhouse gas (GHG) fluxes in wetland ecosystems, but the mechanisms of plant removal and plant species that contribute to GHG emissions remain unclear. In this study, the fluxes of carbon dioxide (CO(2)) and nitrous oxide (N(2)O) were measured using the static chamber method from an island forest dominated by two different species, namely Betula platyphylla (BP) and Larix gmelinii (LG), in a marsh wetland in the Great Xing’an Mountains. Four sub-plots were established in this study: (1) bare soil after removing vegetation under BP (SBP); (2) bare soil after removing vegetation under LG (SLG); (3) soil with vegetation under BP (VSBP); and (4) soil with vegetation under LG (VSLG). Additionally, the contributions of the dark respiration from plant aerial parts under BP (VBP) and LG (VLG) to GHG fluxes were calculated. We found that the substantial spatial variability of CO(2) fluxes ranged from −25.32 ± 15.45 to 187.20 ± 74.76 mg m(−2) h(−1) during the study period. The CO(2) fluxes decreased in the order of SBP > VSLG > VSBP > SLG > VLG > VBP, indicating that vegetation species had a great impact on CO(2) emissions. Particularly, the absence of vegetation promoted CO(2) emission in both BP and LG. Additionally, CO(2) fluxes showed dramatically seasonal variations, with high CO(2) fluxes in late spring (May) and summer (June, July, and August), but low fluxes in late summer (August) and early autumn (September). Soil temperatures at 0–20 cm depth were better predictors of CO(2) fluxes than deeper soil temperatures. N(2)O fluxes were varied in different treatments with the highest N(2)O fluxes in SLG and the lowest N(2)O fluxes in VBP. Meanwhile, no significant correlation was found between N(2)O fluxes and air or soil temperatures. Temporally, negative N(2)O fluxes were observed from June to October, indicating that soil N(2)O fluxes were reduced and emitted as N(2), which was the terminal step of the microbial denitrification process. Most of the study sites were CO(2) sources during the warm season and CO(2) sinks in the cold season. Thus, soil temperature plays an important role in CO(2) fluxes. We also found that the CO(2) flux was positively related to pH in a 10 cm soil layer and positively related to moisture content (MC) in a 50 cm soil layer in VSBP and VSLG. However, the CO(2) flux was negatively related to pH in a 30 cm soil layer in SBP and SLG. Our findings highlight the effects of vegetation removal on GHG fluxes, and aid in the scientific management of wetland plants.