Invasive water lettuce ( <i>Pistia Stratiotes</i> ) increase CO ₂ /CH ₄ emissions from a subtropical lake in Huixian wetland (Southwest China)

Despite tropical and subtropical aquatic systems suffering from increasing invasion of floating plants, the effects of floating plants invasion on aquatic greenhouse gas (GHG) emissions remain poorly understood. In this study, CO2 and CH4 fluxes were measured in water lettuce (Pistia stratiotes) and open water areas in Huixian wetland in Guangxi, Southwest China, from November 2020 to November 2021. Our results indicated that CO2/CH4 emissions showed obvious seasonal variations, CO2 fluxes for the water lettuce and open water zones showed a significant CO2 sink in winter, and CH4 fluxes for the water lettuce showed a maximum emission in September 2021. The annual cumulative CO2 fluxes for the water lettuce zone were 5,578.63 ± 957.99 g m−2 yr−1, which were significantly higher than that from the open water area (2,551.77 ± 482.49 g m−2 yr−1). Likewise, the annual cumulative CH4 emissions from the water lettuce area (693.39 ± 142.88 g m−2 yr−1) were significantly higher than those from the open water zone (119.17 ± 4.45 g m−2 yr−1). CO2 fluxes were significantly positively correlated with air and water temperature, and significantly negatively correlated with TN and DO. CH4 fluxes were significantly negatively correlated with HCO3−. This study indicated that the increased invasion of water lettuce may enhance GHG emissions from a subtropical lake, thus contributing to global warming. More attention should be paid to the invasion of floating plants into subtropical karst lakes because geological conditions and aquatic plants might significantly influence greenhouse gas emissions.