Temporal changes in functional diversity of culturable bacteria populations in Sitka spruce stumps

Changes in culturable aerobic bacterial communities of Sitka spruce stumps between 1 and 10 years old were investigated by isolating from the top 55 mm of the stumps. High numbers of bacteria were recovered from 15 mm below the surface of 1- and 2-year-old stumps, particularly in the sapwood, after which numbers dropped by an order of magnitude. Proportions of colony-forming units (cfu) capable of degrading cellulose and chitin increased with stump age, whereas siderophore producers decreased. Colony-forming units were grouped on the basis of 13 phenotypic characteristics, including colony form and colour, Gram stain, heat tolerance, siderophore production and production of various enzymes. Four groups of bacteria were identified; the proportions of the three Gram-negative groups varied with stump age. A quadratic relationship between bacterial diversity and stump age was detected using the Shannon-Weaver diversity index. Bacterial diversity was higher 15 mm below the stump surface than in deeper sampling points. The results are discussed in terms of the possible influence of prokaryotic organisms on the development of decay communities in Sitka spruce stumps.