BACTERIAL COMMUNITY STRUCTURE AT DEFINED LOCATIONS OF PINUS-SYLVESTRIS SUILLUS-BOVINUS AND PINUS-SYLVESTRIS PAXILLUS-INVOLUTUS MYCORRHIZOSPHERES IN DRY PINE FOREST HUMUS AND NURSERY PEAT

Bacteria were isolated and characterized from uncolonized soil, nonmyc orrhizal and mycorrhizal short roots, and soil-colonizing external myc elium from intact Pinus sylvestris - Suillus bovinus and Pinus sylvest ris - Paxillus involutus mycorrhizospheres developed in microcosms con taining dry pine forest humus or nursery peat. Total numbers of colony -forming units (CFU/mg dry weight) in the different locations from all ectomycorrhizospheres indicated an overall bacterial-enrichment gradi ent towards the roots, whereas sporeformers were more evenly distribut ed. Fluorescent pseudomonads were commonly isolated from all mycorrhiz osphere locations in nursery peat, but they were nearly absent from th e forest humus community. In contrast, sporeformers were more abundant at all locations in the latter growth substrate. The;bacterial specie s composition of forest and nursery mycorrhizospheres was clearly dive rgent when characterized according to their carbon source utilization patterns in Biolog(R) GN or GP microplates. Factorial-designed ANOVA o f a principal component analysis of the carbon source utilization data showed significant differences between isolates from the two soil typ es and, to a lesser extent, between S. bovinus and Paxillus involutus mycorrhizospheres. Bacterial communities from mycorrhizospheres and un colonized soil were distinguished by their preferential utilization of carbohydrates and organic and amino acids, respectively. Suillus bovi nus associated bacteria appeared to favour mannitol and Paxillus invol utus associated bacteria appeared to favour fructose as carbon sources . This study demonstrates the combined effect of soil type, fungal sym biont, and precise location on bacterial communities associated with P inus sylvestris ectomycorrhizospheres.