SUMMARY: A study has been made, using a plating technique, of the fungi occurring in acid sandy podsol soils and of their distribution at different levels of the soil profile. The most widespread species, characteristic of this type of soil, included: and A number of other species were locally abundant, including sp., sp. (roscum series), and

The plate counts of viable fungal units decreased sharply from upper to lower levels, though there was occasionally a secondary maximum in the upper part of the B horizon. Most species were characteristically found most abundantly in upper layers of the A horizon, but was notable for its abundance at much lower levels; in several of the profiles examined it was isolated in almost pure culture from the B horizon.

Of the sixty-five species isolated, about half produced antibiotics. Most of these were toxic to fungi and bacteria; only a few cases of specific antifungal or antibacterial activity were encountered. The Phycomycetes differed from other groups in that none produced antifungal substances. The capacity to produce antifungal antibiotics appears to be correlated with the distribution of species; of the widespread and locally abundant fungi, 45% produced such antibiotics as compared with 15% of the rare fungi. Nevertheless, certain widespread species (e.g. ) did not produce antifungal antibiotics, so it cannot be considered to be a necessary character of widespread soil fungi. There is some evidence that such widespread non-producers of antibiotics are relatively resistant to the antibiotics produced by other species.

An attempt has been made to group the fungi isolated into Burges' ecological categories of ‘sugar-fungi’ and ‘humus-fungi’ on the basis of their capacity to attack and utilize carboxymethylcellulose (CMC). Only 26% of the fungi were unable to utilize CMC, Phycomycetes being prominent among these. Whereas 35% of the rare fungi and 54% of locally abundant fungi were ‘sugar-fungi’, only 17% (all Phycomycetes) of the widespread fungi were ‘sugar-fungi’.

These results are believed to lend support to the view that antibiotic production is of ecological significance to soil fungi. They also provide information which can form the basis of an experimental search for more direct evidence.


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