Effects of pentachlorophenol and 2,4,5-trichlorophenoxyacetic acid on the microflora of the soil in a beech wood

Summary Every second month for 2 years a beech forest floor was treated with pentachlorophenol and 2,4,5-trichorophenoxyacetic acid each in two concentrations. The microbial biomass and its respiration activity in the three litter horizons were measured during this time and during a recovery period of 2 years after the treatment was stopped. The microbial biomass, mainly fungi, was decreased dose-responsively, as was the respiration rate. The doubling time of the fungal biomass was estimated to be about 50–100 days in the F horizon, and considering the natural decreases and recovery times observed, it is suggested, following Domsch et al. (1983), that a biomass decrease of 75%–93.75% is tolerable, a decrease of less than 75% is negligible, and a decrease of over 93.75% is critical.