Effect of the chlorinated hydrocarbon herbicide, paraquat dichloride, on the growth properties and diversity of soil fungi

Abstract

This study explored acute herbicide-induced changes in soil fungal biomass, relative abundance, diversity and hyphal extension in response to five different application concentrations (1.625mg/kg – 25.00mg/kg) of paraquat dichloride using the media dilution technique. There was a general decline in all the parameters investigated with increasing concentration and contact time. Of all the isolates obtained, Penicillium and Fusarium were the most frequently occurring amongst the filamentous fungi while Saccharomyces was the more frequently occurring yeast. Investigation of soil mycelial biomass revealed that the lowest dry weight was attained at the highest application rate of 25mg/kg representing a 61.71% reduction in mycelial biomass compared to the control. Based on the tolerance indices, the three isolates studied could be ranked in increasing order of tolerance as Mucor < Fusarium < Penicillium. Mucor showed no linear extension at concentrations of 3.25mg/kg and above while Penicillium exhibited linear extension even at 25mg/kg. At paraquat dichloride concentrations of 6.50mg/kg and over, growth inhibition levels for total soil fungi were over 50%; for Mucor, it was 100% at concentrations over 3.25mg/kg. Fusarium only exhibited 100% growth inhibition at the highest application concentration of 25mg/kg. Penicillium and total soil fungi were inhibited by 94% and 75% respectively at 25mg/kg. Statistically, soil fungal abundance and linear extension at herbicide concentrations of 3.25mg/kg and over were significantly different (at 95% confidence interval) from those obtained in the control experiments. It was concluded that the soil fungal community structure was radically altered by acute exposure to the herbicide, paraquat dichloride.