Variation in soil microbial communities: elucidating relationships with vegetation and soil properties, and testing sampling effectiveness

Abstract

Understanding the extent of heterogeneity in soil microbial community structure and function at different scales within vegetation communities is critical to designing appropriate sampling protocols. Environmental factors (e.g. disturbance) make sampling in the riparian zone particularly challenging as vegetation communities are highly heterogeneous. To assess whether heterogeneity in soil and vegetation factors is reflected in microbial communities, a study was conducted in a riparian area in southern Australia. Nine quadrats were established encompassing different environmental conditions. Within quadrats physical, chemical and biological soil properties were analysed at two depths (top-soil = 0–10 cm and sub-soil = 20–30 cm), and floristic composition of ground cover, sub-canopy and canopy vegetation assessed. Soil biological analyses included microbial community composition (genetic analysis using ITS and 16S regions), and function (microbial metabolic activity using EcoPlates). Variation in soil microbial communities (fungi, bacteria, archaea) was related to differences in vegetation factors, particularly sub-canopy, and to a lesser extent, soil chemical properties. Relationships between variation in microbial communities and vegetation composition were stronger in top-soil than sub-soil. These observations were consistent for fungal communities excluding the phylum Glomeromycota, where the relationship was stronger with ground cover and only for top-soil. Variation in soil microbial community function was not related to variation in microbial community composition, soil physicochemical properties or vegetation factors. Our findings suggest there is little variation in the composition of soil microbial communities within areas with similar vegetation, and a small sampling effort would be needed to adequately describe the characteristics of such soil communities.