The Effect of Soil Texture on Richness and Diversity of Bacterial Communities

Bacterial diversity in soil is high relative to more homogeneous environments (e. g., freshwater or marine habitats). Isolation imparted by fragmented aquatic microhabitats in unsaturated soil likely plays a large role in creating this diversity. We evaluate the role of soil texture, which determines the extent and connectivity of microhabitats, in constraining bacterial diversity. Soil samples with a range of textures were collected from sixteen sites across Connecticut and Massachusetts. Soil particle size distributions were measured to determine soil texture (% sand, % silt and % clay). Soil chemical characteristics (e. g., pH, %, % N) that might influence diversity were quantified for each site. Terminal restriction fragment length polymorphism (T-RFLP) analysis was performed to characterize the diversity (richness, Shannon's H', and evenness) of soil bacterial communities. Bacterial species richness increased significantly (p = 0.04) with the coarseness of the soil, quantified as % sand. No trend in H' or E were observed; all communities exhibited high diversity and evenness. The increase in species richness in coarser soils is likely due to the increased number of isolated water films in soils with larger pores, suggesting that pore-scale hydrologic regime constrains bacterial richness in soil.