Regulation of greenhouse gas emissions and carbon sequestration in wetland by submerged plant mowing time and potential mechanisms.

Mowing is an important submerged plant growth management measure to maintain the balance of inland wetland ecosystems. However, systematic studies on plant mowing time affecting wetland greenhouse gas (GHG) emissions and carbon sequestration remain scarce. In this research a pilot-scale wetland system was established to investigate the effects of submerged plant Ceratophyllum demersum L. mowing time on GHG emissions and carbon sequestration, and metagenomic techniques were employed to explore the functional microorganisms and genes for carbon and nitrogen cycling in wetland. The results showed that C. demersum L. mowing resulted in CO2 flux reduction of 55.76%-79.34%, CH4 flux reduction of 83.54%-99.48%, and N2O flux reduction of 75.80%-82.88%. The optimal plant mowing time was July, achieving abetter trade-off between carbon sequestration and carbon emissions. The C. demersum L. biomass showed obvious temporal dynamics, with the highest biomass for mowing in July, increasing by 12.12% compared with that of control. However, plant mowing slightly reduced the water purification capacity. Microbial analysis revealed that plant mowing downregulated the expression of key functional genes (mcrA, pmoA, norB, nosZ) and decreased the abundance of methanogens and denitrifying bacteria, explaining the reduction in CH4 and N2O fluxes. These findings provide a scientific basis for wetland plant growth management. Future research should explore long-term field validation and effects of environmental variables.