© 1996 Heron Publishing—Victoria, Canada
Functional biodiversity of microbial communities in the rhizospheres of hybrid larch (Larix eurolepis) and Sitka spruce (Picea sitchensis)
Susan J. Grayston and Colin D. Campbell
Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, U.K. / Received October 25, 1995
Summary
The diversity of microorganisms associated with trees and their different functional capabilities is thought to be a consequence
of variation in carbon compounds in the rhizosphere. We used the Biolog® system (Biolog Inc., Hayward, CA), a redox-based
test, to construct sole carbon source utilization profiles (metabolic fingerprints) of microbial communities from the rhizospheres
and rhizoplanes of hybrid larch (Larix eurolepis A. Henry) and Sitka spruce (Picea sitchensis Bong. Carr.) taken from a farm woodland site and two second-rotation plantation forest sites. Canonical variate analysis
(CVA) of carbon utilization data 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 acids were
the substrates responsible for this discrimination. Carbon profiles of the microbial communities from the rhizospheres of
the two tree species also clustered when evaluated by CVA, as a result of differences 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 and quantitative differences in the culturable populations of microorganisms 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 substrates available in the particular ecosystem under study.
Keywords:
Biolog, carbon utilization profiles, metabolic fingerprints, root exudates.
