EFFECT OF HIGH CO2 AND LOW O2 TENSIONS ON THE SOIL MICROBIOTA

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Abstract
The influence of high pCO2 and low pO2 on the microbiota derived from four tropical soils and on microorganisms in pure culture was investigated. Incubation under atmospheres containing more than 90% CO2 reduced the number of organisms developing on soil dilution plates, but most organisms recovered when the plates were subsequently incubated in air. Inhibition by high CO2 tensions was the result primarily of CO2 concentration and not absence of O2; many organisms developed under 100% N2, and presence of O2 mitigated the inhibitory effects, especially when CO2 concentration was 95% or less. The actinomycete population was most sensitive to high pCO2 and low pO2 and the fungal population least sensitive. Some fungi were capable of developing under 100% N2 and under atmospheres containing as much as 98% CO2; most identified species developed in air after exposure to the various gases. Fusarium oxysporum f. cubense was more tolerant to low O2 and high CO2 tensions than most of the soil mycobiota.