Spatial distribution of soil microbial activity and soil properties associated with Eucalyptus and Acacia plantings in NSW, Australia

Abstract

Although much work has been completed in Australia to examine the effects on aboveground ecology of environmental plantings using mixed species of native trees, only limited attention has been focused on their effects on soils and soil microbial population. A study was conducted to determine the spatial distribution of microbial activity, total soil organic carbon (TOC), total nitrogen (TN) and extractable phosphorus (P) in soils under Eucalyptus camaldulensis and Acacia pendula. A 13-year-old environmental planting with mixed native tree species at Gunnedah, New South Wales, was used as a study site. Soil samples were taken from both inside and outside the tree canopy at each of the four compass points (N, S, E and W) at depths of 0–5, 5–10, 10–20, 20–30 and 30–50 cm. The soil was tested for heterotrophic respiration (MicroRespTM), TOC and TN (LECO) and P (Colwell). Microbes were more active inside compared with outside the tree canopy in both A. pendula and E. camaldulensis. The basal respiration rate was significantly higher under A. pendula canopy compared with E. camaldulensis canopy. The relative activity of the microbes and concentrations of TOC, TN and P declined with soil depth. Further, TOC, TN and P contents under the canopy of A. pendula were higher than those of E. camaldulensis and showed a significant positive correlation with basal respiration. However, no difference was detected in the various soil properties measured and microbial activity at four compass points around trees. Changes in soil TOC, TN and extractable P due to the tree plantings were significant only for the 0–5 cm soil depth and changes in microbial activity were mostly confined to the upper 20 cm depth. The improved levels of soil microbial activity and soil nutrients under the tree canopy could be used to measure restoration success of environmental plantings.