Microbial Functional Diversity - Assessing Impacts of Forest Management Practices.
Briony M. Lalor1, Natasha C. Banning1, W. Richard Cookson1, Carl D. Grant2, and Daniel V. Murphy1. (1) School of Earth and Geographical Sciences, Faculty of Natural and Agricultural Science, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, Australia, (2) Environmental Department, Alcoa World Alumina, PO Box 172, Pinjarra, Perth, Australia
Identifying tools which provide an understanding of how key ecological processes in forest ecosystems respond to anthropogenic disturbances or changes in management practises (e.g. burning, logging) is critical for sustainable forest management. Despite wide recognition that the soil microbial community is fundamentally important in mediating key ecological processes such as organic matter turnover and nutrient cycling, few studies have examined the recovery of these processes following disturbances in forest systems. Although diversity of higher organisms is considered important for the maintenance and stability of ecosystem processes, the question remains as to whether this is true for soil microbial communities. Even with the latest molecular genetic techniques, analysis of the vast genetic and taxonomic diversity of soil microorganisms is problematic. As the functional ability of the soil microbial community is central to understanding key ecological processes, a popular alternative has been to assess the diversity of heterotrophic functions. However, a rapid screening method is required to enable the microbial heterotrophic functional ability to be utilized as an indicator of recovery of soil function. There are currently two methodologies used to assess the diversity of heterotrophic ability or Community Level Physiological Profiles (CLPP) from whole soil. Both methods measure the metabolism of a range of organic substrates which vary in structural complexity. The method developed by Degens and Harris (1997) has been useful in assessing CLPP of soils under changing land-uses, from soils under successional series or from soils which have undergone recent disturbances. However, this technique is time-consuming and laborious when analyzing large numbers of samples, undermining its utility as a rapid assessment tool. Campbell et al. (2003) have recently developed an innovative microtiter plate based method (MicroRespTM) that allows the rapid assessment of metabolic response using a colormetric detection system and an automated plate reader. No comparison has previously been made between the Degens and Harris method and the MicroRespTM method. To test the ability of the two methods to distinguish between soils under different forest management, we used soil collected from rehabilitated bauxite mined forest and adjacent non-mined Jarrah (Eucalyptus marginata Donn ex Sm) forest soil from Western Australia. Multivariate statistical analysis demonstrated that the CLPP data generated using the MicroRespTM method resulted in greater pooling of replicates and was substantially better able to discriminate between the soils tested than that of the Degens and Harris method. In addition to greater discriminating ability, the MicroRespTM method has clear advantages over the Degens and Harris method, with the ability to test up to 96 substrates simultaneously on one plate. As a result the MicroRespTM method allows rapid optimization of substrates to suit the ecosystem of interest. Changing forest management practises can alter organic matter quality and quantity, which can in turn impact microbial turnover of organic matter and subsequent nutrient transformations. By including ecologically relevant carbon substrates such as plant root exudates or substrates known to be produced following a specific management practice (e.g. products of fire), the CLPP data generated can be more relevant to the forest ecosystem being investigated. At present we are optimizing the range of substrates required to determine whether prescription burning practises are influencing CLPP within rehabilitated bauxite mined forest and non-mined jarrah forest ecosystems. As the automated and cost efficient nature of the MicroRespTM method makes it a suitable rapid assessment tool, we believe it can be used to compliment other approaches such as bio-molecular methods and NMR, when assessing the impact of forest management on soil processes. A further explanation of the differences in discriminating ability of the two methods and the ecological significance to rehabilitated jarrah forest ecosystems will be discussed in detail.