Effects of atmospheric ammonia and ammonium sulphate on vesicular–arbuscular mycorrhizal colonization in three heathland species

Abstract

Three heathland species. Arnica montana L., Viola canina L. and Nardus stricta L., were exposed to gaseous ammonia and artificial rain containing ammonium sulphate for 11 wk. Plants infected with Glomus fasciculatum (Thaxter Sensu Gerdemann) Gerd & Trappe grew faster than non-mycorrhizal plants. Ammonia increased the shoot dry weight of both mycorrhizal and non-mycorrhizal V. Canina and mycorrhizal N. stricta. Only mycorrhizal V. canina and non-mycorrhizal N. stricta grew faster when supplied with increasing concentrations of ammonium sulphate. The nitrogen tissue concentration, in all three species, was not influenced by vesicular-arbuscular mycorrhiza (VAM), but increased when plants Wete treated with ammonia. Mycorrhizal and non-mycorrhizal N. stricta and mycorrhizal V. canina had a higher N tissue concentration when supplied with ammonium sulphate. The phosphorus tissue concentration was higher when plants were infected VAM, but tended to be lower in the presence of ammonia or ammonium sulphate. Mycorrhizal plants had higher total amounts of N and P than non-mycorrhizal plants and plants treated with ammonia had higher total amounts of N than non-treated plants. VAM colonization increased in all three species when treated with ammonia but was not affected by exposure to ammonium sulphate. Mycorrhiza decreased the sensitivity of N. stricta to drought, while ammonia decreased the sensitivity to drought for all three species. The effects of additional nitrogen in relation to N/P ratios are discussed with respect to the ecological consequences for these heathland species.