INTERACTION OF SUBSTRATE C:N RATIO AND OSMOTIC POTENTIAL ON GROWTH AND OSMOREGULATION OF FOUR FILAMENTOUS FUNGI

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Abstract
Variation in the carbon to nitrogen ratio in the range 10:1 to 1000:1 had only a small effect on the radial growth rate of four species of fungus on a basic nutrient agar medium. There was no obvious pattern to the differences observed, whether the nitrogen source was organic or inorganic or the medium osmotic potential high or low. The final fresh weight of the colonies was more sensitive to C:N ratio and was depressed by high C:N ratios by as much as 90% in some treatments. Polyporus versicolor L. ex Fr. was the most efficient accumulator of biomass at C:N of 1000:1, but Penicillium chrysogenum Thom had the highest mycelial N content. Colony yield did not show the same relationship to external osmotic potential as did the radial growth rate, and the ratio at which the maximum yield at each osmotic potential occurred varied with the different treatments. Turgor potential was reduced by high C:N in the majority of treatments in Polyporus versicolor, Poria vincta (Berk.) Cke. and Phytophthora cinnamomi Rands but not at all in Penicillium chrysogenum. Water content increased with the C:N ratio and decreased with external osmotic potential in all the species except Phytophthora cinnamomi. There was no clear effect of C:N ratio in any of the hyphal solutes measured, that is Na+, K+, Cl-, proline or glycerol. Lower concentrations of the organic solutes were present in Phytophthora cinnamomi and Penicillium chrysogenum in these conditions than when KCl and Czapek-Dox with yeast extract medium was used; turgor potential of Penicillium chrysogenum also was 50% lower. Sodium chloride was used to adjust the external osmotic potential and Na+ and Cl- were taken up in increasing amounts as the osmotic potential decreased in all species. Potassium concentrations were similar between species and treatments. The hyphal osmotic potentials, calculated from these solutes alone, were lower (more negative) than the values measured in Poria vincta grown at -1 MPa and Penicillium chrysogenum grown at -10 MPa [megapascal] but very close to those for Phytophthora cinnamomi grown at -2.5 MPa.

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