Symbiotic Fungi Determine Plant Community Structure: Changes in a Lichen- Rich Community Induced by Fungicide Application

Abstract

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 rangiformis from the community and resulted in a large increase in the cover of the moss Ceratodon purpureus. There were also changes in the frequencies of several higher plant species in response to benomyl application. There were significant reductions in mycorrhizal colonization following fungicide application in Crepis capillaris and Erodium cicutarium, which were reduced in abundance by benomyl application, whereas the non-mycorrhizal Arenaria serpyllifolia and Rumex acetosella increased in abundance in fungicide-treated plots. Changes in the frequencies of mycorrhizal higher plant species were negatively correlated with reductions in mycorrhizal colonization of their root systems. There was also a 22% increase in plant species density m -2 in plots treated with benomyl. Ordination analyses showed that 60% of the variation in the vegetation data set could be accounted for by Carex arenaria, 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 sets of plots were vegetationally distinct. The results show that two groups of symbiotic fungi are important regulators of plant community structure: the lichen C. rangiformis was a keystone organism in the community studied and appeared to be able to suppress the moss C. purpureus, and arbuscular mycorrhizal fungi appeared to play a significant role in determining the interspecific competitive abilities of higher plant species.