Temporal analysis of the soil microbial community along a toposequence in Pineland soils

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The stability and function of a soil ecosystem depends on the cycling of nutrients by the soil microbial community. To evaluate native variability in the functional soil microbial community, temporal changes in microbial community size, activity and metabolic diversity were measured by bacterial population densities, microbial biomass, dehydrogenase activity and metabolic diversity (BIOLOG) assays in native New Jersey Pineland soils. Native soils were sampled and assessed seasonally for five consecutive seasons along a toposequence with an O horizon that varied in organic matter (1.0–91.7%) and a water content that ranged from well-drained to poorly drained (0.21–4.30 g water g −1 dry wt soil). Significant differences ( P<0.05) were found in bacterial population densities, microbial biomass, and dehydrogenase activity between soil types in each sampling period. Seasonal variability was found in bacterial populations and dehydrogenase activity, but not in microbial biomass. Principal component analysis (PCA) revealed consistent differences in the metabolic diversity patterns of the A horizon of the low organic, xeric upland microbial community as compared to the transitional and lowland soil microbial communities. When the upland O and A soil horizons were compared, the two horizons showed different metabolic diversity patterns. Metabolic diversity patterns varied little over time, indicating a stable functional heterotrophic microbial community. The various indicators of microbial community dynamics used in this study demonstrated general seasonal microbial activity differences associated with a reasonably stable microbial biomass and metabolic diversity. Factors affecting metabolic diversity appeared to be linked closely with variation in the composition of the vegetation in the aboveground community along the toposequence.