Soil microbial communities and activities in sand dunes of subtropical coastal forests

Abstract To understand the soil microbial activities and community structures in different forests in a sand-dune ecosystem, we conducted a study of 2 topographic conditions, upland and lowland, under a Casuarina forest. As well, in the lowland site, we compared forest soil microbial properties under 3 coastal forests ( Casuarina , Hibiscus and mixed stand). The soil microbial biomass did not significantly differ between the upland and lowland Casuarina forest sites. At the lowland site, the soil microbial biomass was higher in the Hibiscus than Casuarina forest soil. Cellulase, xylanase, phosphatase and urease activities did not show a consistent trend by topography or vegetation. Analysis of phospholipid fatty acids (PLFAs) of bacteria and actinomycetes revealed a significant difference in microbial community structure by both topography and vegetation. PLFA content was higher at upland than lowland sites in the Casuarina forest. At the lowland site, the level of PLFAs was higher in Hibiscus than Casuarina forest soil. In addition, we examined the ratios 16:1ω7t/16:1ω7c and, cy17:0/16:1ω7c as indicators of physiological stress; the soil in the Casuarina forest had the highest values, which suggests that the microbial community in the Casuarina forest soil is under physiological stress or starvation conditions. Comparison of soil microbial properties suggest that planting Hibiscus may help to enrich soil fertility and increase microbial activities in coastal sand-dune Casuarina forest.