Microbial production of ethylene in desert soils

Ethylene production was monitored in 12 desert soils. In all but two soils with high organic matter content, C₂H₄ production was low. Statistical analysis showed a good correlation between organic matter content and C₂H₄, production. Minimum levels of C₂H₄ were observed in saline and sodic soils. Addition of l-methionine to soil significantly increased C₂H₄ formation, indicating its possible role as a precursor for C₂H₄. Addition of salt to the high C₂H₄-producing soils suppressed C₂H₄ production most probably because of a direct effect on C₂H₄-producing microorganisms through toxic salt levels, high osmotic pressure, increased pH or a combination of these factors. Leaching of four saline soils and subsequent incubation resulted in significant increases in C₂H₄ in two soils. Ethylene producers, previously inhibited by salinity, were probably reactivated when the salts were removed. A Fusarium isolated from the high C₂H₄-producing soil, produced the most C₂H₄ in pure culture followed by isolates belonging to the genera Aspergillus, Penicillium, Curvularia and Rhizopus. A sterilized saline soil produced significant C₂H₄ when inoculated with spores of Mucor hiemalis or the Fusarium isolate, indicating an originally low population of C₂H₄-producing organisms in the saline soil. The two high organic matter soils when sterilized and similarly inoculated produced only a fraction of the C₂H₄ produced in non-sterilized samples, indicating the involvement of a number of species in the production of C₂H₄ in these soils.