Metabolic activity and population dynamics of rhizobia introduced into unamended and bentonite-amended loamy sand

Abstract

Respiration measurements showed that the cumulative amount of CO2 respired by rhizobia introduced into sterile bentonite-amended loamy sand was significantly higher than it was in unamended loamy sand. The maintenance respiration of rhizobial cells was not influenced by the presence of bentonite clay. Carbon was used more efficiently during growth in bentonite- amended than in unamended loamy sand. The presence of bentonite clay increased the growth rate of rhizobia introduced into sterile soil. Survival studies performed in nonsterile bentonite-amended loamy sand showed that the use of high (1010 cells per g of dry soil) rather than lower (104 to 107 cells per g of dry soil) inoculum densities increased the final survival levels of introduced rhizobia. In unamended loamy sand, the application of 1010 or 107 cells per g of dry soil resulted in similar final survival levels. Pore shape and the continuity of the water-filled pore system were suggested to largely determine the colonization rate of protective microhabitats.