Soil bacterial community responds to land-use change in riparian ecosystems

Background and Objectives: Riparian forests were frequently cleared and converted to agricultural pastures. In recent times these pastures are often revegetated in an effort to return riparian forest structure and function. We tested if there is a change in the soil bacterial taxonomy and function in areas of riparian forest cleared for agricultural pasture, then revegetated; and if soil bacterial taxonomy and function is related to vegetation and soil physicochemical properties. Materials and Methods: The study was conducted in six study areas in south - eastern Australia, each comprising of three land-use types: remnant riparian forest, cleared forest converted to pasture and revegetated pastures. We surveyed three strata of vegetation and sampled top-soil and sub-soil to characterize physicochemical properties. Taxonomic and functional composition of soil bacterial communities were assessed using 16S rRNA gene sequences and community level physiological profiles respectively. Results: Few soil physiochemical properties differed with land-use despite distinct vegetation in pasture relative to remnant and revegetated areas. Overall bacterial taxonomic and functional composition of remnant forest and revegetated soils were distinct from pasture soil. Land-use differences were not consistent for all bacterial phyla, as Acidobacteria were more abundant in remnant soils, conversely Actinobacteria were more abundant in pasture soils. Overall bacterial metabolic activity, and soil carbon and nitrogen content decreased with soil depth, while bacterial metabolic diversity and evenness increased with soil depth. Soil bacterial taxonomic composition was related to soil texture and soil fertility, while functional composition was only related to soil texture. Conclusions: Our results suggest that the conversion of riparian forests to pasture is associated with significant changes in the soil bacterial community, whereby revegetation contributes to reversing such changes. Nevertheless, the observed changes in bacterial community composition (taxonomic and functional) were not directly related to changes in vegetation, but were more closely related to soil attributes.