N-133. Impacts of Water Stress on Carbon Monoxide-Oxidation in Recent Volcanic Deposits

C. F. Weber, G. M. King;
Louisiana State Univ., Baton Rouge, LA.

Water availability oscillates dramatically on young volcanic deposits and likely plays a significant role in controlling the distribution and activity of microbes throughout biological succession. In this study, we examined the effects of water potential on the activity of carbon monoxide (CO)-oxidizing bacteria in unvegetated (Bare) and vegetated (Canopy) sites on a 1959 volcanic deposit on Kilauea Volcano (Hawaii). Throughout the day, water potentials varied little in the top 2 cm of Canopy soil (-0.0 MPa to -0.2 MPa), while water potentials varied dramatically in Bare site surface tephra. On clear days, morning dew on the surface tephra resulted in water potentials near -0.0 MPa, but water potentials measured near midday were as low as -93 MPa. However, water potential measurements of subsurface layers of the Bare site (3-15 cm) were at or near -0.0 MPa. Despite dramatic fluctuations in water potential in the Bare site surface tephra, vertical profiles of CO oxidation rates revealed that the fastest rates of CO-oxidation are present in the surface. CO-oxidation and growth by strains of Mycobacteria, Burkholderia and Mesorhizobium isolated from volcanic deposits were completely inhibited at water potentials at and below -2.2 MPa. Preliminary activity data suggests that this may also be the case for CO-oxidizing communities in the Bare and Canopy sites. However, surface material from Bare and Canopy sites stored in a desiccator for 12 days (<-300MPa) resumed CO oxidation at near pre-desiccation rates after rewetting. Collectively, these results indicate that in situ CO-oxidation may cease rapidly as water potentials drop below -0.0 MPa, but may resume rapidly upon rewetting. Such resilience may contribute to the ability of CO-oxidizers to persist in water stressed substrates during the early stages of biological succession.