Abstract: Spartina alterniflora invasion changes the function and balance of mangrove ecosystem. However, the effects of S. alterniflora invasion on soil phosphorus (P) fractions, P-cycling functional genes and their interactions are still unclear. In this study, we examined the variations of soil physical and chemical properties, P fractions, soil microorganisms and P-cycling functional genes across four different vegetation types (Kandelia obovata, Aegiceras corniculatum, Avicennia marina, Spartina alterniflora) in Zhangjiang Estuary. The results showed that: (1) The content of soil stable P was the highest, followed by moderately labile P, and the content of labile P was the least. The content of labile P in S. alterniflora soil was 91.7-143.8 mg·kg^-1, which was significantly higher than that in the three mangrove soils. The content of moderately labile P in K. obovata soil was 266.13±24.94 mg·kg^-1, which was the highest among the four vegetation types, indicating the largest supply potential of P. The content of stable P did not vary among different vegetation types. (2) S. alterniflora invasion increased α diversity and changed microbial community composition, while decreased the relative abundance of most P-cycling microorganisms. (3) P regulation and transportation genes were dominant in soil P cycling genes across the four vegetation types. The relative abundance of P regulation genes (PhoB, PhoR, PhoU) and transportation genes (PstSCAB, PhnCDE, ugpBACE) in A. marina soil was the highest, while S. alterniflora soil was the lowest. Therefore, S. alterniflora invasion led to the change of soil P cycle by changing the soil physical and chemical properties and consequently the composition of microbial community and gene expression.

Key words: Spartina alterniflora, wetland ecosystem, soil phosphorus fraction, metagenomics