Abstract
Riparian forests were frequently cleared and converted to agricultural pastures, but 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. The study was conducted in six riparian 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 surface soil and subsoil 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. 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, but functional composition was only related to soil texture. Our results suggest that the conversion of riparian forests to pasture is associated with significant changes in the soil bacterial community, and that 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.
Highlights
Land-use change can strongly affect vegetation, soil physicochemical properties, and soil bacterial communities [1,2,3,4]
We aimed to address the following questions: (a) Does soil bacterial community composition change with the conversion of riparian forest to agricultural pasture? (b) To what extent does revegetation of pasture restore the soil bacterial community composition to its original state? (c) Do land-use change effects on bacterial composition differ in the surface soil (0–10 cm) relative to subsoil (20–30 cm)? (d) Which vegetation properties and/or soil physicochemical properties better predict the soil bacterial community composition? We hypothesized that bacterial community composition would change with land use and soil depth
Our results suggest that revegetation has contributed to the return of some components of bacterial taxonomic diversity, but recovery is lacking in some phyla (e.g., Acidobacteria, Actinobacteria, Gemmatimonadetes, and Firmicutes)
Summary
Land-use change can strongly affect vegetation, soil physicochemical properties, and soil bacterial communities [1,2,3,4]. Bacterial community abundance, composition, and activity may be critical in improving soil properties and increasing plant establishment after land-use change [7,8,9]. Previous studies have shown differences in the soil bacterial communities were related to exotic and native groundcover vegetation [17]. These vegetation-driven changes in soil bacteria may be a bacterial response to plant root exudations, which are carbon-based compounds comprised of organic acids, carbohydrates, and amino acids [18,19]
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