Pastures to woodlands: changes in soil microbial communities and carbon following reforestation

Abstract

Reforestation of agricultural lands has the potential to sequester C, while providing other environmentalbenefits. It is well established that reforestation can have a profound impact on soil physicochemicalproperties but the associated changes to soil microbial communities are poorly understood. Therefore,the objective of this study was to quantify changes in soil physicochemical properties and microbialcommunities in soils collected from reforested pastures and compare then to remnant vegetation and un-reforested pastures. To address this aim, we collected soil from two locations (pasture and its adjacentreforested zone, or pasture and its adjacent remnant vegetation) on each of ten separate farms thatcovered the range of planting ages (0–30 years and remnant vegetation) in a temperate region ofsoutheastern Australia. Soils were analysed for a range of physicochemical properties (including C andnutrients), and microbial biomass and community composition (PLFA profiles). Soil C:N ratios increasedwith age of tree planting, and soil C concentration was highest in the remnant woodlands. Reforestationhad no clear impact on soil microbial biomass or fungal:bacterial ratios (based on PLFA’s). Reforestationwas associated with significant changes in the molecular composition of the soil microbial community atmany farms but similar changes were found within a pasture. These results indicate that reforestation ofpastures can result in changes in soil properties within a few decades, but that soil microbial communitycomposition can vary as much spatially within pastures as it does after reforestation.