The effect of floating vegetation on CH4 and N2O emissions from subtropical paddy fields in China

Duckweed (Lemna minor), a floating macrophyte belonging to the Lemnaceae family, is commonly found in subtropical paddy fields. This plant rapidly takes up nutrients from water and forms dense floating mats over the water surface that may impact the biogeochemical processes and greenhouse gas production in paddy fields. In this study, we measured CH4 and N2O emissions from duckweed and non-duckweed plots in a subtropical paddy field in China during the period of rice growth using static chamber and gas chromatography methods. Our results showed that CH4 emission rate ranged from 0.19 to 26.50 mg m(-2) h(-1) in the duckweed plots, and from 1.02 to 28.02 mg m(-2) h(-1) in the non-duckweed plots. The CH4 emission peak occurred about 1 week earlier in the duckweed plots compared to the non-duckweed counterparts. The mean CH4 emission rate in the duckweed plots (9.28 mg m(-2) h(-1)) was significantly lower than that in non-duckweed plots (11.66 mg m(-2) h(-1)) (p < 0.05), which might be attributed to the higher water and soil Eh in the former. N2O emission rates varied between -50.11 and 201.82 A mu g m(-2) h(-1), and between -28.93 and 54.42 A mu g m(-2) h(-1) in the duckweed and non-duckweed plots, respectively. The average N2O emission rate was significantly higher in the duckweed plots than in the non-duckweed plots (40.29 vs. 11.93 A mu g m(-2) h(-1)) (p < 0.05). Our results suggest that the presence of duckweed will reduce CH4 emission, but increase N2O flux simultaneously. Taking into account the combined global warming potentials of CH4 and N2O, we found that growing duckweed could reduce the overall greenhouse effect of subtropical paddy fields by about 17 %.