Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081186

    In situ characterization of soil microbe function in an ICH chronosequence
Project lead: Jones, Melanie (University of British Columbia)
Contributing Authors: Brooks, Denise; Jones, Melanie D.; Grayston, Susan J.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
The project addresses high priority topics of the Sustainability Program Eligible Research Topics 2007/08: Theme 1. Ecosystem structure and processes, and biodiversity related to forest management; Topic 1.2. Soil biology, ecology, and productivity; Priority b. Evaluating the relationships between soil biology/ecology and soil productivity In forest soils, ectomycorrhizal (ECM) fungi give roots increased access to nutrients such as nitrogen and phosphorus by releasing enzymes that break down soil organic matter. However, ECM fungal species differ from each other in this ability.
This will be the first study to examine in-situ changes in enzyme activity in ECM communities over successional time and to link them with forest management. The community of ECM fungi changes substantially following clearcutting (Jones et al. 2003). Work from an earlier FSP project was the first to determine that it takes approximately 65 years for the species composition of the ECM fungal community to stabilize in ICH forests after disturbance (Twieg 2006). However, we do not know how long it takes for the ECM fungal community to develop a full complement of nutrient cycling abilities. This might occur prior to stabilization of the fungal species composition because of redundancy in function amongst the 15,000 ECM fungal species thought to exist. Knowledge about the functional maturity of the soil microbial community will assist in the planning of harvesting patterns. It is important to leave a sufficient area of mature forest soil as an inoculum source for adjacent harvested areas.
This knowledge is not available elsewhere because ours is the only group in North America looking at physiology of ECM communities as it relates to forest management. By comparing microbial development following natural disturbance (wildfire) and clearcutting, we will continue to contribute to ecosystem management strategies. We will continue to work at a series of chronosequence sites in the ICH characterized by Twieg: four age classes of post-fire disturbance forest plots: young (3-6 years), canopy closure (24-27 years), stem exclusion (55-60 years), and older (88-100 years). The chronosequence also has stands in the younger two age classes that have regenerated from clearcuts. The chronosequence sites have been carefully selected to include mixed Douglas-fir/paper birch stands. We will learn whether birch-specific fungi have a unique functional role in organic matter degradation. We have developed and tested novel in-situ methods for studying the function of microbial communities at these sites. These rapid enzyme assays record enzyme activity directly from the soil profile and provide qualitative enzyme activity information. Our results indicate a marked shift in the quality of acid phosphatase activity in the stem exclusion age class with areas of phosphatase activity becoming larger and more intense than those seen either in the younger or canopy closure age classes and becoming similar to the profile seen in the older age class. We will investigate the ECM fungal contribution to this change in soil enzyme activity. One of our objectives will be to determine when the enzyme profile associated with the mycorrhizal hyphae is typical of a mature forest soil. We will use a new field-based method for isolating ECM hyphae in-situ which traps mycorrhizal hyphae and associated bacteria in sand-filled mesh bags (Wallander et al. 2001). We will test the organic matter-degrading ability of the mycorrhizal hyphae from these bags by quantifying the activities of phosphatase, -glucosidase, phenol oxidase, N-acetylglucosiminidase, and peroxidase (Sinsabaugh et al. 1999). This suite of enzymes breaks down chitin, cellulose, lignin, and organic phosphorus compounds to release nitrogen and phosphorus in forms that can be absorbed by roots and fungi. As soil bacteria also produce degradative enzymes, we will also use sand bags that trap soil bacteria while excluding hyphae in order to determine the relative enzyme activity contribution of ECM fungi versus soil bacteria. The hyphal sand bags will provide us unique access to a bacterial community strongly influenced by ECM fungi. The function of this community is largely unknown. These bacteria may be competing with ECM for nutrients (Koide et al. 2001) and/or complementing and amplifying ECM function through enzyme production (Colpaert and vanLaere 1996). Recent work has shown that the hyphal growth of certain ectomycorrhizal species is selectively promoted by some actinobacteria, while the growth of other species is inhibited (Riedlinger et al. 2006). The actinobacteria are also known for their antibiotic production and their inhibition of fungal pathogens (Axelrood et al. 1996). Therefore an additional goal will be to isolate and identify unique actinomycetes from the ECM-influenced bacterial community and visualize the interaction of these bacteria with ECM to determine if they play an important role in mycorrhiza function.
The results of this study will allow forest managers to plan cutting regimes with an increased understanding of the development of ICH soils. It is important that sites with a complement of physiologically diverse ECM fungi be present in the landscape. Some ECM fungi do not disperse effectively from spores and rely primarily on root-to-root spread. Therefore, patches of mature forest soils will act as sources of inoculum of mycorrhizal fungi with specific functional traits. Our comparison of sites regenerating from wildfire and clearcut logging will give forest managers a concrete baseline for evaluating whether forest management practices are maintaining soil microbial community functionality compared to natural disturbance regimes. This study will build on a growing body of research focused on the effects of forest management on microbial communities and the importance of these microbial communities to forest ecosystem function.
Related projects:  FSP_Y092186


Executive Summary (23Kb)
Root Window Technique Poster (91Kb)
Phosphorus Cycling Poster (0.1Mb)

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Updated August 16, 2010 

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