Limits to Microbial Growth in Soil

More organic carbon was released into solution from soils that had been air-dried and rewetted than from the natural soils. Irradiation and autoclaving of a range of air-dried or field soils greatly increased the amount of carbon that was released into solution. The carbon released appeared to provide substrates for fungal spore germination and bacterial growth, thereby relieving microbiostasis. The percentage germination of Penicillium citrinum spores was at least doubled in sterilized soil and halved in untreated soil compared with spores germinating in the absence of soil. In general, a streptomycin-resistant strain of Agrobacterium radiobacter made significant growth only in sterilized soils.