Comparison of two methods that assess soil community level physiological profiles in a forest ecosystem

There are currently two approaches that use whole soil to determine community level physiological profiles (CLPP) based on C-substrate utilization. We assessed the Degens and Harris and MicroResp™ approaches for their ability to distinguish between previously mined and non-mined forest soils that are characterized by gradients in biological, chemical and physical properties. Surface soils (0-5 cm) were collected from two ages of forest rehabilitation (3- and 16-years post mining), within mounds and furrows (caused by contour ripping) and from adjacent non-mined forest soil. Microbial respiration response to individual substrates was six times greater from the Degens and Harris (1.84 μg CO₂-C g soil h⁻¹) than the MicroResp™ (0.31 μg CO₂-C g soil h⁻¹) approach. The MicroResp™ approach was able to distinguish between CLPP of the two ages of rehabilitation (P=0.05), whereas the Degens and Harris approach did not. Neither approach identified an overall difference between the CLPP of mined and adjacent non-mined forest. The MicroResp™ approach revealed a significant difference (P=0.03) in CLPP from mounds of the two rehabilitation ages but no differences between the furrows. In addition there was a difference (P=0.03) in CLPP between the mounds and furrows within the 3-year old rehabilitation but no difference between the mounds and furrows within the 16-year-old rehabilitation. However, the CLPP of mounds of the 3-year old rehabilitation were different (P=0.059) to adjacent non-mined forest, while the furrows were not. There was no difference in CLPP between the mounds or the furrows of the 16-year-old rehabilitation and adjacent non-mined forest. These results suggest that the aspect of microbial heterotrophic function measured in this study takes up to 3 years to re-establish in the furrows and between 3-16 years in the mounds of post-mined rehabilitation soils. Our results also indicated that the MicroResp™ was substantially better than the Degens and Harris approach in distinguishing between treatments; this is likely to be due to differences in substrate concentrations and soil water potentials between approaches. Testing of a more comprehensive range of organic compounds would likely provide greater ecological interpretation of the CLPP data.