Bacterial movement at high matric potentials—I. In artificial and natural soils

Abstract

The rate of active movement of five isolates from three genera of soil bacteria in an artificial and a natural soil at high matric potentials was studied. In nutrient-amended soils the order of motility at matric potentials of —50cm and —150cm of water was: Pseudomonus fluorescens > Bacillis subtilis (two isolates) > Azotobacter vinelandii > Azotobacter chroococcum. The rate of movement of all organisms was markedly greater at the same potential in the artificial soil than in the natural soil. The faster rate in the artificial soil was attributed to the lack of a component with a high surface charge density, onto which bacteria became adsorbed. Though the influence of soil physical factors on microbial activities may be more easily studied in artificial soil systems, the lack of such a component may limit its usefulness in interpreting activities involving adsorption phenomena. Thus, while A. vinelandii moved 26mm in 48 h in the artificial soil at —50cm matric potential, there was negligible movement (5 mm in 48 h) at the same potential in the natural soil. The results indicate that, in contrast to P. fluorescens, Bacillus subtilis and Azatobacter spp. are unlikely to move appreciably through natural soil at matric potentials of less than —150cm of water.