ADAPTATION OF THE SOIL MICROBIOTA TO HIGH CO2 AND LOW O2 TENSIONS

Abstract

The ability of the soil microbiota to adapt to atmospheres of high CO₂ and low O₂ tensions was investigated. Subsamples of soil were incubated (conditioned) in gases containing different concentrations of CO₂ and O₂, and the tolerance to adverse atmospheric conditions of organisms subsequently isolated was compared with that of organisms present in the soil before conditioning. Although apparent adaptation of the fungal, bacterial, and actinomycete populations occurred, it was not established whether physiological adaptation, rather than enrichment of segments within the populations tolerant to these conditions, occurred. Adaptation appeared to be enhanced by conditioning the soil in gases similar to, but not the same as, that under which the organisms were subsequently isolated. Although adaptation, in general, increased as the CO₂ tension of the conditioning atmospheres decreased, the CO₂ concentration, rather than reduced O₂ tensions, induced adaptation. Aspergillus, Fusarium, Penicillium, and Trichoderma exhibited greater tolerance and adaptability to high CO₂ and low O₂ tensions than other genera of the mycobiota. Possible implications of the capacity to adapt to adverse atmospheric conditions in the ecology of microorganisms in soil are discussed.