SYMBIOTIC FUNGI DETERMINE PLANT COMMUNITY STRUCTURE - CHANGES IN A LICHEN-RICH COMMUNITY INDUCED BY FUNGICIDE APPLICATION

1. The fungicide benomyl was applied to a lichen-rich plant community growing on a sandy soil in Suffolk, UK, once a month from November to May for 3 years. Benomyl application eliminated the lichen Cladonia ra ngiformis from the community and resulted in a large increase in the c over of the moss Ceratodon pulpureus. There were also changes in the f requencies of several higher plant species in response to benomyl appl ication. 2. There were significant reductions in mycorrhizal colonizat ion following fungicide application in Crepis capillaris and Erodium c icutarium, which were reduced in abundance by benomyl application, whe reas the non-mycorrhizal Arenaria serpyllifolia and Rumex acetosella i ncreased in abundance in fungicide-treated plots. Changes in the frequ encies of mycorrhizal higher plant species were negatively correlated with reductions in mycorrhizal colonization of their root systems. The re was also a 22% increase in plant species density m(-2) in plots tre ated with benomyl. 3. Ordination analyses showed that 60% of the varia tion in the vegetation data set could be accounted for by Carer arenar ia, Cladonia rangiformis and R. acetosella on the first component axis , and by Ceratodon purpureus, Hypnum cupressiforme var. lacunosum and Cerastium fontanum on the second axis, and demonstrated that the two s ets of plots were vegetationally distinct. 4. The results show that tw o groups of symbiotic fungi are important regulators of plant communit y structure: the lichen C. rangiformis was a keystone organism in the community studied and appeared to be able to suppress the moss C. purp ureus, and arbuscular mycorrhizal fungi appeared to play a significant role in determining the interspecific competitive abilities of higher plant species.