ROOT SYMBIOSES OF ALNUS-GLUTINOSA (L) GAERTN AND THEIR POSSIBLE ROLE IN ALDER DECLINE - A PRELIMINARY-STUDY

During the last few years alder has declined in South Bohemia. The pos sible role of mycorrhizal and actinorhizal symbioses is reviewed and s ome of the preliminary results from experiments testing the influence of these symbioses on alder growth and the influence of eutrophication on the development of these symbioses are reported. Seedlings of Alnu s glutinosa were inoculated with arbuscular mycorrhizal (AM) fungi and the actinomycete Frankia in experiment I,and with rhizosphere soil co llected from field sites with different degrees of alder damage in exp eriment 2. In both experiments, a solution containing nitrate, ammonia and phosphorus in concentrations simulating eutrophic waters, was app lied. Both symbioses markedly promoted the growth of the seedlings in experiment 1. The plants inoculated with the rhizosphere soil microflo ra in experiment 2 were larger than the control plants. Response of th e seedlings to the inoculation with the soil from the rhizosphere of d amaged alder trees from six field sites differs, even though no correl ation was found relating growth to the health status of the trees. Nut rient treatment did not have any effect on the growth of seedlings in either experiment. The dry weight of Frankia was greater in mycorrhiza l plants compared to nonmycorrhizal plants and mycorrhizal colonizatio n is reduced in Frankia inoculated plants supplemented with phosphorus in experiment 1. Nitrogen enhanced mycorrhizal colonization in nodula ted plants which were not supplemented with phosphorus no effect of ni trogen on actinorhiza was observed.