The Effects of Agrochemicals on Litter Fungi

Abstract

The effects of the fungicides CAPTAN and VERDASAN, and the herbicides, MAZIDE, PARAQUAT, and 2,4,5-trichlorophenoxyacetic acid (2,4,5T) on the occurrence and physiology of fungi inhabiting the litter layer were studied. When applied at normal field rates, the fungicides slightly reduced the total fungal numbers and species numbers isolated from leaf litter of Agrostis tenuis, although there were little or no effects with the herbicides at either normal field rate or elevated rates. When applied at a rate three times greater than normal field rate the fungicides drastically reduced the number of species isolated, although only CAPTAN markedly reduced the total number of isolations. The species composition of the leaf litter mycoflora was also altered: Alternaria alternata and Ulocladium botrytis showed increased incidence from fungicide-treated leaves, although Epicoccum purpurascens and Fusarium spp. were reduced. U. botrytis was recorded as the major component of VERDASAN-treated leaf litter. Its numbers increased dramatically when the fungicide was applied at the higher rate. An attempt was made to isolate Basidiomycetes from a number of cellulosic substrates, and one which was successfully isolated was used in subsequent physiological studies. The growth of a number of mycorrhizal and non-mycorrhizal Basidiomycetes was studied. The non-mycorrhizal fungi showed higher growth rates than the mycorrhizal forms in media, both with and without agrochemical addition. The results obtained with Phallus impudicus indicated that it was more comparable with the mycorrhizal species. The effects of PARAQUAT and VERDASAN on the leakage of potassium, phosphate and amino acide from mycorrhizal and nonmycorrhizal Basidiomycetes were also studied. The mycorrhizal species generally leaked cellular metabolites faster and more copiously than the non-mycorrhizal species in the presence of agrochemicals. The organo-mercurial fungicide VERDASAN was shown to inhibit cellulase activity of a Basidiomycete found inhabiting leaf litter.