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

Colonization of the spermosphere and rhizosphere by plant-beneficial bacteria is limited by competition with indigenous soil microbes for resources such as reduced carbon compounds. A study of the soil microbial community around germinating seeds was undertaken as a necessary first step in understanding the competition between the introduced plant-beneficial bacteria and the indigenous microbial community. Two soil types, Galestown gravely loamy sand soil, with pH 5.8 and 0.6% humic material, and Hatborough loamy sand soil, with pH 4.5 and 3.2% humic material, were compared. Five seed types, corn, cucumber, radish, soybean, and sunflower were used. Microbial communities were characterized functionally, using a substrate utilization assay, and structurally, using fatty acid methyl ester analysis, over a 96-h period after the onset of germination. Soil type affected the microbial communities far more than seed type. The communities in Hatborough soil had greater functional and structural changes compared with the control than Galestown soil. The communities changed more functionally than structurally, with increased substrate utilization compared with the soil controls.