Changes in methane emission and methanogenic and methanotrophic communities in restored wetland with introduction of Alnus trabeculosa

Purpose: The dynamics and uncertainties in wetland methane budgets affected by the introduction of Alnus trabeculosa H. necessitate research on production of methane by methanogenic archaea and consumption by methane-oxidizing microorganisms simultaneously. Materials and methods: This study investigated methane emission in situ by the closed chamber method, and methanogenic and methanotrophic communities using denatured gradient gel electrophoresis (DGGE) and quantitative PCR based on mcrA (methyl coenzyme M reductase), pmoA (particulate methane monooxygenase) genes in the rhizosphere and non-rhizosphere soils in the indigenous pure Phragmites australis T., and A. trabeculosa–P. australis mixed communities in Chongxi wetland. Results and discussion: Methane flux rate from the pure P. australis community was 2.4 times larger than that of A. trabeculosa–P. australis mixed community in the rhizosphere and 1.7 times larger in the non-rhizosphere, respectively. The abundance of methanogens was lower in the mixed community soils (3.56 × 10³–6.90 × 10³ copies g⁻¹ dry soil) compared with the P. australis community (1.47 × 10⁴–1.89 × 10⁴ copies g⁻¹ dry soil), whereas the methanotrophs showed an opposite trend (2.08 × 10⁶–1.39 × 10⁶ copies g⁻¹ dry soil for P. australis and 6.20 × 10⁶–1.99 × 10⁶ copies g⁻¹ dry soil for mixed community soil). A liner relationship between methane emission rates against pmoA/mcrA ratios (R² = 0.5818, p < 0.05, n = 15) was observed. The community structures of the methane-cycling microorganism based on mcrA and pmoA suggested that acetoclastic methanogens belonging to Methanosarcinaceae and a particular type II methanotroph, Methylocystis, were dominant in these two plant communities. Conclusions: The introduction of A. trabeculosa would promote the proliferation of methanotrophs, especially the dominant Methylocystis, but not methanogens, ultimately diminishing methane emission in the wetland.