Effects of Pinus sylvestris root growth and mycorrhizosphere development on bacterial carbon source utilization and hydrocarbon oxidation in forest and petroleum-contaminated soils

The hypothesis that Pinus sylvestris L. root and mycorrhizosphere developme nt positively influences bacterial community-linked carbon source utilizati on, and drives a concomitant reduction in mineral oil levels in a petroleum hydrocarbon- (PHC-) contaminated soil was confirmed in a forest ecosystem- based phytoremediation simulation. Seedlings were grown for 9 months in lar ge petri dish microcosms containing either forest humus or humus amended wi th cores of PHC-contaminated soil. Except for increased root biomass in the humus/PHC treatment, there were no other significant treatment-related dif ferences in plant growth and needle C and N status. Total cell and culturab le bacterial (CFU) densities significantly increased in both rhizospheres a nd mycorrhizospheres that actively developed in the humus and PHC-contamina ted soil. Mycorrhizospheres (mycorrhizas and extramatrical mycelium) suppor ted the highest numbers of bacteria. Multivariate analyses of bacterial com munity carbon source utilization profiles (Biolog GN microplate) from diffe rent rhizosphere, mycorrhizosphere, and bulk soil compartments, involving p rincipal component and correspondence analysis, highlighted three main nich e-related groupings. The respective clusters identified contained bacterial communities from (i) unplanted bulk soils, (ii) planted bulk PHC and rhizo spheres in PHC-contaminated soils, and (iii) planted bulk humus and rhizosp here/mycorrhizosphere-influenced humus, and mycorrhizosphere-influenced PHC contaminated soil. Correspondence analysis allowed further identification of amino acid preferences and increased carboxylic/organic acid preferences in rhizosphere and mycorrhizosphere compartments. Decreased levels of mine ral oil (non-polar hydrocarbons) were detected in the PHC-contaminated soil colonized by pine roots and mycorrhizal fungi. These data further support our view that mycorrhizosphere development and function plays a central rol e in controlling associated bacterial communities and their degradative act ivities in lignin-rich forest humus and PHC-contaminated soils.