EFFECTS OF ATMOSPHERIC AMMONIA AND AMMONIUM-SULFATE ON VESICULAR-ARBUSCULAR MYCORRHIZAL COLONIZATION IN 3 HEATHLAND SPECIES

Three heathland species, Arnica montana L., Viola canina L. and Nardus stricta L., were exposed to gaseous ammonia and artificial rain conta ining ammonium sulphate for 11 wk. Plants infected with Glomus fascicu latum (Thaxter sensu Gerdemann) Gerd. and Trappe grew faster than non- mycorrhizal plants. Ammonia increased the shoot dry weight of both myc orrhizal and non-mycorrhizal V. canina and mycorrhizal N. stricta. Onl y mycorrhizal V. canina and non-mycorrhizal N. stricta grew faster whe n supplied with increasing concentrations of ammonium sulphate. The ni trogen tissue concentration, in all three species, was not influenced by vesicular-arbuscular mycorrhiza (VAM), but increased when plants we re treated with ammonia. Mycorrhizal and non-mycorrhizal N. stricta an d mycorrhizal V. canina had a higher N tissue concentration when suppl ied with ammonium sulphate. The phosphorus tissue concentration was hi gher when plants were infected with VAM, but tended to be lower in the presence of ammonia or ammonium sulphate. Mycorrhizal plants had high er total amounts of N and P than non-mycorrhizal plants and plants tre ated with ammonia had higher total amounts of N than non-treated plant s. VAM colonization increased in all three species when treated with a mmonia but was not affected by exposure to ammonium sulphate. Mycorrhi za decreased the sensitivity of N. stricta to drought, while ammonia d ecreased the sensitivity to drought for all three species. The effects of additional nitrogen in relation to N/P ratios are discussed with r espect to the ecological consequences for these heathland species.