Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 65. (Budapest 1973)
Bohus, G.: Soil acidity and the occurrence of fungi in deciduous forests
Accordingly, subsequent research took two courses. Physiological experiments were conducted, and soil pH measured in situ of the fruitbodies. Physiological experiments with macro-fungi have been conducted by many authors with the application of synthetic culture media (15 species have been investigated in this regard in the framework of the present study). However, the results obtained could be connected only with difficulties with observations in the field, if only for the reason that applied culture media have compositions widely different from those of the respective soils. According to the composition of the culture media, diverse inferences can be drawn. Some examples are highly illustrative: if in the modified Treschow solution the carbon source is saccharose, then, in the case of either a glycocoll or a pepton nitrogen source, Agaricus macrosporoides practically stops to grow about 7 pH, but development is rather satisfactory about 4 pH (in our own experiments). If, however, the carbon source is d-glucose, then a normal growth of uniform rate ensues about both 7 pH and 4 pH (Table 3). In LINDEBERG'S experiments with Marasmius graminum, "the calcium ion was effective in overcoming the toxic effect of an initial pH of 3.3". Looking for some other method, the thought arose to examine the regulating ability of the mycelia or fruitbodies of fungus species — the ability to influence the acidity of their immediate site — with a view to obtain, if at all, data connectible with field observations by which one might infer that certain species not only tolerate but definitely prefer certain pH values. Method 1. Determining the regulating ability of the fruitbody and the mycelium Rir-ACEK's method (1948, 1966), applied for other objects, was modified at a rate necessary for fungi and used as follows : 10x5x5 mm bits were cut with rust-proof knife from fresh fruitbodies. Ten pieces each were placed for 1 hour at 24 C° in 30 ml solutions with their pH set by 0.01 in NaOH and HCl solutions at 3, 4, 5, 6, 7, 8 pH. After 1 hour, the altered pH values were measured by electric pH-meter and glass electrode. Concerning regulation, the ratio 10 pieces of fruitbody and 30 ml solution proved to be satisfactory (Table 4). It seems that the loose or more compact state of the fruitbodies can be left out of consideration in determining the appropriate number of fruitbody prisms (Table 5), but they must be fresh and healthy. Thin fruitbodies (e. g. Gortinarius vibratilis) are not suitable for the experiments. Lactarius fruitbodies secreting latex copiously are also unsuitable, because it is not known to what extent the comparatively greater amount of latex modifies pH. To study mycelial regulation, the mycelium of the given species are incubated in modified Treschow culture solution (50 ml solution on 100 ml test flasks) at 24 C° until it extends over the surface, then after removing the solution the mycelium is shaken with 80 ml distilled water at 24 C°, and then again soaked in 100 ml distilled water for 15 minutes. After pouring off the water for washing, 10 ml of the various solutions set at various pH (as given above) is added to the mycelium. The material is incubated at 24 C° for 1 hour, and then the pH measured. The washed-out rate of the solutions proved to be sufficient in the course of control measurements (Table 6,7). The rate of development of the mycelia has no effect on the rate of regulation. After investigations running through the entire series it was found that it is generally sufficient to determine the regulating ability of the mycelium or the fruitbody in solutions with pH values 4 and 5. Among the terricolous macro-fungi, the humicolous species, living exclusively on a thick litter cover, were left out of consideration. These species have hardly any connection with the soil under the leaf litter, and thus the effect of soil acidity is hardly or only moderately prevailing (IIINTIKKA 1970). 2. Measuring soil pH values The soil samples were taken at the site of growth of the fruitbodies, the homogenized material of a 0-20 cm section. The proportion of material and the boiled distilled w T ater was 1:2.5. Mixing with water was made on the day following sampling (the soil samples •5 Természettudományi Múzeum Évkönyve 1973.
