Impacts of vegetation, tidal process, and depth on the activities, abundances, and community compositions of denitrifiers in mangrove sediment.

Coastal mangrove wetland is well known to be intense in nitrogen cycling. The tidal process and plants are key factors in controlling the microbial processes in wetlands. However, mechanisms on how these factors and their interactions affect the microorganisms involved in denitrification remain poorly understood. In this study, the impacts of vegetation (bulk, Kandelia obovata, and Spartina alterniflora) and tidal process (falling tide and rising tide) on denitrification activities, abundances, and community compositions of denitrifiers in the sediments from different depths (0-5 and 5-10 cm) were investigated in a microcosm experiment. A significant enhancement of denitrification activities and gene abundances (nirS, nirK, and nosZ) in the vegetated sediments was observed. Activities and abundances were significantly higher in the 0-5-cm sediments when compared with the 5-10-cm counterparts. The effect of interaction between vegetation and tide or depth was also significant. Terminal restriction fragment length polymorphism (T-RFLP) analysis revealed that not only vegetation but also plant species had a significant impact on the community compositions of nirK denitrifiers, while the tidal process affected the community compositions of nirS and nosZ denitrifiers but not nirK denitrifiers. However, depth only significantly shaped the nirS denitrifier communities. These findings demonstrate the effects of these factors and their interactions in shaping the denitrifiers in sediments.