Soil microbial characteristics in the rhizosphere of Sonneratia caseolaris and S. apetala forests at different stand ages in Shenzhen Bay

The present study examined the relationships between rhizosphere soil characteristics, microbial community and microbial activities in the forests artificially planted with two Sonneratia species at different stand ages (1-, 2-, 7-, 10- and 14-year-old for S. apetala and 1-, 4-, 7-, 10- and 14-year-old for S. caseolaris) in Futian National Nature Reserve, Shenzhen Bay. The rhizosphere soils in S. apetala and S. caseolaris forests at different stand ages were neutral or slightly acidic. The soil organic matter content increased with stand ages, but the total nitrogen (N) and total phosphorus (P) contents increased significantly only from 1- to 7-year-old stands and then decreased with ages. The temporal changes of the microbial biomass carbon, as well as the population sizes of bacteria, fungi and actinomycetes, were similar, with the maximum values in the 7-year-old forest. The microbial respiration rate in S. caseolaris was less than that in S. apetala at the same stand age. The microbial respiration rate increased with ages in S. caseolaris, but reached the peak value in the 7-year-old S. apetala forest. The canonical correlation analysis showed that the microbial biomass carbon and respiration rate in the rhizosphere were significantly correlated with soil organic matter content and pH.