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AN INVESTIGATION INTO THE POSSIBLE CHANGES IN THE MICROBIAL POPULATION OF SOILS STORED AT — 15°C

E. GROSSBARD and D. M. HALL
Plant and Soil
Vol. 21, No. 3 (December 1964), pp. 317-332
Published by: Springer
Stable URL: http://www.jstor.org/stable/42932076
Page Count: 16
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AN INVESTIGATION INTO THE POSSIBLE CHANGES IN THE MICROBIAL POPULATION OF SOILS STORED AT — 15°C
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Abstract

The effect of storing soils at — 15°C on their microbial populations has been investigated. The counts of actinomycetes, bacteria, and fungi in soils stored frozen for various periods of time and thawed differ from those obtained from unfrozen soils. The differences are sometimes negligible, but extreme changes do occur. Counts of actinomycetes, and to some extent (though less consistently) those of bacteria, tend to fall with time of storage, while fungal counts increase in at least two out of four experiments. The most extreme differences are not associated with any specific period of storage. Some of the variations observed may possibly have been due to errors in sampling and counting rather than to genuine population changes. A drop in counts could have been anticipated in view of the known adverse effects of low temperatures on micro-organisms. The increase in colony counts is tentatively explained as resulting from a better release and dispersion of propagules due to the enhanced disintegration of soil and microbial aggregates brought about by freezing and thawing. Contributing biological factors may be a short burst in growth of cold-resistant organisms during the process of freezing and thawing and some stimulatory effects of low temperatures on germination, akin to vernalization. Although the true nature of any changes will not be fully elucidated until better sampling and counting methods have been developed the evidence presented here suggests that the storage of soils at sub-freezing temperatures cannot be regarded as a safe means of preserving the microbial equilibrium as it existed at collection time in the soil samples.

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