No abstract

To investigate the possible natural development of heavy metal tolerance in VA-mycorrhizal fungi, plants of Agrostis capillaris from an uncontaminated, a copper-contaminated and a zinc/cadmiumcontaminated area were examined for VA-mycorrhizal infection. During a period of 5 years (1987 to 1991) the plants of the copper-tolerant population were hardly infected, whereas the population on the uncontaminated soil showed a mean infection of nearly 60% and the zinc/cadmium-tolerant population of 40%. A detailed analysis of the surroundings of the copper-enriched site revealed the presence of VA-mycorrhizal fungi and a negative correlation between the infection rate of A. capillaris and the copper content of the soil. In contrast to the copper-contaminated soil, the abundant presence of VA-mycorrhizal fungi in the area contaminated by zinc and cadmium indicates that these fungi have evolved a zinc and cadmium tolerance and that they may play a role in the zinc and cadmium tolerance of A. capillaris.

Three populations of the perennial grass Agrostis capillaris, growing on limestone derived clay with and without natural enrichment of the heavy metals cadmium, lead, and zinc, and on a sandy soil polluted by a metal smelter have been investigated with regard to the percentage and seasonality of infection with vesicular-arbuscular mycorrhizal (VAM) fungi and its impact on mineral nutrition.In all populations VAM infection was lowest during winter, and highest during late summer and autumn. The population at the metal smelter site was less infected by VAM fungi than both other populations. The concentration of mineral nutrients for the three populations was clearly related to the soil concentration, but hardly modified by the degree of VAM infection.

Hybridization and introgression between Quercus robur and Q. petraea was investigated in 12 Dutch populations, using multivariate analysis. Compared with the reference groups, the differences between the two taxa are slight, but distinct. The Q. petraea types differ more from their reference group than the Q. robur types, possibly due to greater selection pressure. In most populations a range of specimens occurs between pure Q. robur and pure Q. petraea. The latter category is poorly represented, and actual F,-and F 2-hybrids are most uncommon. Products ofintrogression between primary hybrids and Q. robur as well as Q. petraea constitute an important part of the populations. Hybridization and introgression is partly due to planting of Q. robur by man. In the natural population of the Meinweg a gradient is established between Q. robur in the lower, moist levels and Q. petraea in the higher, relatively dry levels.

Male sterility was investigated in 19 Dutch Origanum vulgare populations by counting stamens and relating the numbers to several environmental factors. A mean of 11.5% male sterility was found for all populations, while 12 populations had a low value ofQ-4.5~~~and the other 7 a higher one of 8.9-64.2%. Of the 53 plants counted 43% showed no staminal reduction and 57% a reduction of0.2-100%. Only 2 plants were found with a IOO~, reduction, which is c. 4%. Considerable variation inmale sterility was established for individual plants within one population and also, rather frequently, for different stems on one plant. Of 4384 flowers counted 9.5% had no stamens, while 1.3;', had I, 1.5% had 2 and 1.0% had 3 well developed stamens. The remaining 86.7% had all 4 stamens welldeveloped. It was found that populations growing in relatively undisturbed Mesobromionl Trifolion vegetation possessed low male sterility values, and that populations in disturbed Arrhenatherion] Lolio-Potentillion vegetation often had much higher male sterility percentages. Further it was ascertained that small, isolated populations usually had a much higher male sterility than compact populations. No correlations could be found between male sterility and the following environmental factors: acidity, calcium, phosphorus, organic matter, sand. clay, gradient and aspect.