Microbial community structure and function in the spermosphere as affectedby soil and seed type

Colonization of the spermosphere and rhizosphere by plant-beneficial bacter ia is limited by competition with indigenous soil microbes for resources su ch as reduced carbon compounds. A study of the soil microbial community aro und germinating seeds was undertaken as a necessary first step in understan ding the competition between the introduced plant-beneficial bacteria and t he indigenous microbial community. Two soil types, Galestown gravely loamy sand soil, with pH 5.8 and 0.6% humic material, and Hatborough loamy sand s oil, with pH 4.5 and 3.2% humic material, were compared. Five seed types, c orn, cucumber, radish, soybean, and sunflower were used. Microbial communit ies were characterized functionally using a substrate utilization assay, an d structurally, using fatty acid methyl ester analysis, over a 96-h period after the onset of germination. Soil type affected the microbial communitie s far more than seed type. The communities in Hatborough soil had greater f unctional and structural changes compared with the control than Galestown s oil. The communities changed more functionally than structurally, with incr eased substrate utilization compared with the soil controls.