Changes to the structure and function of microbial communities in Spartina alterniflora and Kandelia obovata sediments as a factor of stand age

Abstract

The effects of Kandelia obovata introduction and Spartina alterniflora invasion on the microorganisms are very important for coastal ecology and restoration. MiSeq sequencing of the 16S rRNA gene and Tax4Fun predictive functional profiles were used to investigate the diversity estimators, community structures and potential metabolic functions of benthic bacteria in surface sediments of coastal wetlands invaded by S. alterniflora and artificially planted with K. obovata at stand ages of 2-, 8-, 11-, 16- and 60-years on Ximen Island, Yueqing Bay, China. The results showed that the sediment bacterial richness was significantly decreased in 60-year K. obovata stands compared with younger K. obovata stands and S. alterniflora stands. The age of K. obovata and specie of exotic plants formed distinct bacterial communities and functional structures in sediments, respectively. With increasing plantation of K. obovata, the bacterial communities shifted from the class Anaerolineae, the genus Sulfurovum, and bacteria involved in sulfate reduction as abundant taxa to higher proportions of bacteria involved in degradation of plant polysaccharide and nitrate reduction. The shift in bacterial community structures was mainly driven by changes in sediment total organic matter, total nitrogen, total phosphorus, ammonium concentrations, pH and temperature. The community functions also changed from nitrogen fixation to more nitrate reduction and denitrification processes. Compared with 60-year K. obovata, S. alterniflora was occupied by higher proportions of the phylum Bacteroidetes, the orders Rhodobacterales, Flavobacteriales and Desulfuromonadales, and total nitrogen, total phosphorus concentrations and sediment temperature were major environmental factors affecting the variation. Among the major sulfur cycling processes examined, higher potential of dissimilatory sulfate reduction was observed in S. alterniflora. Our results indicated that K. obovata introduction has a greater effect on the bacterial community diversity and structure than S. alterniflora invasion. This study could improve the understanding of microbial processes and potential functions of K. obovata introduction and S. alterniflora invasion and provide reference in the restoration and management of the coastal wetlands.