Volatiles From Soil Influencing Activities of Soil Fungi

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Abstract
Volatile compounds were detected in natural soils. Among these, dosage-response curves for acetone, ethylene, ammonia and formaldehyde were developed. Concentrations of ethylene and acetone considerably above those detected in soil were necessary to inhibit germination of conidia of test soil fungi. Formaldehyde was detected in some soils at concentrations high enough to inhibit spore germination. Inhibition of conidium germination of Aspgergillus flavus by formaldehyde was nullified by exogenous N and C, but the same phenomenon was not observed for conidia of Fusarium solani f. sp. phaseoli. The ED50 values for conidium germination of Penicillium chrysogenum and Gonatobotrys simplex were below 1 .mu.g ammonia/g air. Reduced germination due to volatiles from 5 soils, limed and not limed, was correlated directly with concentrations of volatile ammonia accumulated for 24 h above these same soils. At certain concentrations, ammonia, ethylene and acetone stimulated growth and/or germination of some of the test organisms. Ammonia must be considered a prime candidate for a volatile inhibitor in soil. Formaldehyde may inhibit some fungi in certain soils. Bioassays provided evidence for another volatile component present in the atmospheres of acid soils. So far, it has not been identified by chemical analysis.

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