Composition of bacterial communities in sand dunes of subtropical coastal forests

Coastal sand dunes are a hostile environment for forests. Little is known about the composition and diversity of the bacterial community in forest soils established on sand dunes. This study examines the soil bacterial community in the upland and lowland Casuarina and lowland Hibiscus successional forests in a coastal sand dune ecosystem. The 16S rRNA gene clone libraries were constructed to analyze the structure and diversity of communities. The Acidobacteria and Proteobacteria predominated in the sand dune forest communities, but the proportions of some phylogenetic groups differed among three communities. Some Actinobacteria- and Bradyrhizobium-related clones were only present or abundant in Casuarina forest soils. Because Casuarina could support a symbiotic, N-2-fixing soil bacterial community, the composition of the microbial community may reflect its potential roles in the nitrogen budget and the effects of vegetation. Based on the diversity indices, the lowland Casuarina soils had the least diverse community, and the upland Casuarina community was the most diverse. Compared to an inland natural forest community, the dune communities were more diverse and had different proportions of abundant bacterial groups from those in the inland soils. The distribution of the abundant operational taxonomic units also differed among coastal and inland forests. The topography and vegetation type could affect the soil bacterial community composition in sand dune forests. The high diversity of soil bacterial community may be a result of the succession phase of the sand dune ecosystem.