Sulphite and ph effects on co2 evolution from decomposing angiospermous and coniferous tree leaf litters

Abstract The relative sensitivities of decomposing leaf litters to low concentrations (12.5–100.0μM) of sulphite were assessed. The experimental litter comprised four broadleaf species ( Ulmus glabra Hudson, Betula sp., Quercus sp., Fagus sylvatica L.) and two conifer species [ Picea sitchensis (Bongard) Carr. and Pinus sylvestris L.]. Carbon dioxide evolution from the coniferous litter was strongly inhibited by SO 3 2− at pH 3.0–6.0, P. sylvestris being the most sensitive of the litters tested. The broadleaf litters were consistently less sensitive than the coniferous litters. The inhibitory effect of SO 3 2− on CO 2 release from litter was increased by increasing the SO 3 2− concentration or decreasing the pH; coniferous litter respiration was inhibited strongly by SO 3 2− at pH 3.0 and 4.0 over 7 days. Spores of Cladosporium cladosporioides (Fres.) de Vries were more sensitive than mycelium growing on decomposing P. sylvestris litter, and both were markedly inhibited by 100.0 μ m SO 3 2− at pH 3.0 for 14 days. The concentrations shown to exert toxicity were the same as those which have been measured in U.K. rainfall and the results provide confirmatory evidence that SO 3 2− exhibits a toxic effect on litter fungi at environmentally-realistic concentrations.