Abstract: To explore the differences in structure and diversity of nirK-type denitrifying microbial community in marsh soils at different invasion stages of Spartina alterniflora, the mudflat (MF, before invasion) and the S. alterniflora marsh after seaward invasion for 1-2 years (SAN) and 6-7 years (SA) in Shanyutan of the Minjiang River estuary were investigated by high-through put sequencing method. Results showed that the seaward invasion of S. alterniflora reduced the richness and diversity of nirK-type denitrifying microbial community in marsh soils. The nirK-type denitrifying microbial community in soils at different invasion stages included Proteobacteria and Actinobacteria, with Proteobacteria as the dominant one. The seaward invasion of S. alterniflora greatly altered the composition of nirK-type denitrifying microbial community in marsh soils. The highest relative abundance of genus in soils from different invasion stages were Bradyrhizobium, Mesorhizobium and Alcaligenes, respectively. The seaward invasion of S. alterniflora increased the spatial heterogeneity of nirK-type denitrifying microbial community composition in marsh soils. In SAN plot, the enhancement of spatial heterogeneity was primarily due to higher environmental disturbances in plots and the increased spatial heterogeneity of environmental variables caused by the seaward invasion of S. alterniflora. The seaward invasion of S. alterniflora altered the physico-chemical properties (e.g., grain composition, pH and moisture) and N nutrient conditions (total N, NH₄⁺-N and NO₃^--N) in marsh soils, which greatly altered the structure and diversity of nirK-type denitrifying microbial community. Our findings reveal the microbial mechanism of denitrification process in marsh soils during the seaward invasion of S. alterniflora.

Key words: nirK, high-throughput sequencing, microbial diversity, community structure, Spartina alterniflora, Minjiang River estuary