Soil microbial activity and nutrient dynamics with soil depth, under mixed tree species environmental plantings in NSW, Australia

Ms Apsara Amarasinghe1, Mrs Christine  Fyfe1, Dr Oliver  Knox1, Associate Professor Lisa  Bruyn1, Associate Professor Paul Kristiansen1, Associate Professor Brian  Wilson1

1School of Environmental and Rural Sciences, Faculty of Science Agriculture Business and Law, University of New England, Armidale, Australia

The impacts of mixed tree species environmental plantings on soil biology is an emerging topic. A pilot study was conducted to determine the variability of microbial activity, total soil organic carbon (C), nitrogen (N) and available phosphorus (P) under Eucalyptus camaldulensis and Acacia pendula used for mixed tree species environmental plantings in NSW. A 13 year old tree planting was selected from a chronosequence of established environmental plantings near Gunnedah, NSW. Soil samples were taken from both inside and outside the tree canopy at depths of: 0–5 cm, 5–10 cm, 10-20 cm, 20-30 cm and 30-50 cm. The soil was tested for heterotrophic respiration (MicroRespTM), total C and N (LECO), and available P (Colwell).

For both tree species, greater microbial activity was observed at: 0-5 and 5-10 cm soil depths compared with the deeper soil layers (20-50 cm). Further, both basal and substrate induced (glucose) respiration rates were higher under the tree canopy compared with outside the tree canopy by 3% and 12%, respectively. Basal respiration rate was significantly higher under E. camaldulensis canopy compared to A. pendula canopy at the 5-10 cm soil depth, however, at 30-50 cm, this result was reversed for the two tree species. For both tree species, C, N and P significantly decreased with depth up to 20 cm. However, no significant difference were detected between 20-30 cm and 30-50 cm. Further, C, N and P contents were lower under the E. camaldulensis canopy than outside whereas, those were not different under and outside of A. Pendula canopy. Under A. pendula the C, N and P were higher than under E. camaldulensis, however, the differences were significant only for total N. Furthermore, microbial respiration was positively correlated with C, N and P. These results suggest trees in environmental plantings do have positive impacts on soil microbial activity and enhance soil nutrient status.


Key Words: Available Phosphorous, Environmental plantings, Microbial respiration, Soil organic carbon, Total nitrogen


Apsara Amarasinghe is a UNE PhD candidate. She completed her Bachelor of Science (Agric) in 2010 and Master of Philosophy in 2017 at Wayamba University of Sri Lanka. Further she has completed a Postgraduate diploma in 2017 at University of Colombo Sri Lanka. She is a Lecturer at Wayamba University of Sri Lanka and obtained International Postgraduate Research Award (IPRA) to carry out her PhD at University of New England. Her PhD is one component of a larger project funded by the Environmental Trust NSW for “Soil biodiversity benefits from environmental plantings”.



7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia


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