Effects of drainage and long-term tillage on greenhouse gas fluxes in a natural wetland: insights from microbial mechanisms.

Abstract

Background: The conversion of natural wetlands to agricultural land through drainage contributes to 62% of the global wetland loss. Such conversion significantly alters greenhouse gas (GHG) fluxes, yet the underlying mechanisms of GHG fluxes resulting from drainage and long-term tillage practices remain highly uncertain. In this study, we measured GHG fluxes of a natural reed wetland (referred to as "Wetland") and a drained wetland that used as farmland (referred to as "Dryland").

Results: The results demonstrated that annual cumulative N₂O and CO₂ fluxes in Dryland were 282.77% and 53.79% higher than those in Wetland, respectively. However, CH₄ annual cumulative fluxes decreased from 12,669.45 ± 564.69 kg·ha^- 1 to 8,238.40 ± 207.72 kg·ha^- 1 in Dryland compared to Wetland. The global warming potential (GWP) showed no significant difference between Dryland and Wetland, with comparable average rates of 427.50 ± 48.83 and 422.21 ± 73.59 mg·CO₂-eq·m^- 2·h^- 1, respectively. Metagenomic analysis showed a decrease in the abundance of acetoclastic methanogens and their functional genes responsible for CH₄ production. Functional genes related to CH₄ oxidation (pmoA) and gene related to N₂O reduction (nosZ) exhibited a substantial sensitivity to variations in TOC concentration (p < 0.05). Candidatus Methylomirabilis, belonging to the NC10 phylum, was identified as the dominant methanotroph and accounted for 49.26% of the methanotrophs. Its relative abundance was significantly higher in Dryland than in Wetland, as the nitrogenous fertilizer applied in Dryland acted as an electron acceptor, with the nearby Wetland produced CH₄ serving as an electron donor. This suggests that Dryland may act as a CH₄ sink, despite the significant enhancement in CO₂ and N₂O fluxes.

Conclusions: In conclusion, this study provides insights into the influence of drainage and long-term tillage on GHG fluxes in wetlands and their contribution to global warming.