FUNCTIONAL BIODIVERSITY OF MICROBIAL COMMUNITIES IN THE RHIZOSPHERES OF HYBRID LARCH (LARIX EUROLEPIS) AND SITKA SPRUCE (PICEA-SITCHENSIS)

The diversity of microorganisms associated with trees and their differ ent functional capabilities is thought to be a consequence of variatio n in carbon compounds in the rhizosphere. We used the Biolog(R) system (Biolog Inc., Hayward, CA), a redox-based test, to construct sole car bon source utilization profiles (metabolic fingerprints) of microbial communities from the rhizospheres and rhizoplanes of hybrid larch (Lar ix eurolepis A. Henry) and Sitka spruce (Picea sitchensis Bong. Carr.) taken from a farm woodland site and two second-rotation plantation fo rest sites. Canonical variate analysis (CVA) of carbon utilization dat a differentiated among the microbial communities from the three forest sites, with the greatest discrimination between the farm woodland and the two second-rotation forest sites. Carbohydrates and carboxylic ac ids were the substrates responsible for this discrimination. Carbon pr ofiles of the microbial communities from the rhizospheres of the two t ree species also clustered when evaluated by CVA, as a result of diffe rences in utilization of carboxylic acids and amino acids, suggesting that these tree species differ in the exudates they produce. Isolation and enumeration of organisms confirmed that there were qualitative an d quantitative differences in the culturable populations of microorgan isms at the different sites and between tree species. We conclude that Biolog is a useful technique for evaluating the functional diversity of microbial communities; however, to interpret the results accurately , they must be assessed in conjunction with the actual carbon substrat es available in the particular ecosystem under study.