Effects of SO 2 and O 3 on the chemistry and fda activity of coniferous leaf litter in an open air fumigation experiment

Abstract

An open-air fumigation facility, developed for continuous fumigation of young conifers by SO 2 and O 3, was used for experimental exposure of decomposing coniferous leaf material. There were no treatment effects on the rates of mass loss from litter for exposure periods from 6 wk to 44 months. Sulphur dioxide treatment consistently increased the rate of removal of base cations from the litter, with the order of sensitivity of cations to SO 2-induced leaching being Mg > Ca > K > Na. The pH of naturally fallen Scots pine needles was reduced by 0.5 units in the high SO 2 treatments. Fluorescein diacetate (FDA) activity and rates of mass loss of naturally-fallen needles were lower in SO 2 fumigated plots than ambient controls. Transplantation experiments showed that the depression in decomposer activity was caused by exposure of needles to SO 2 while still green. Ozone fumigation exerted no effects on the chemical composition of litter, and an O 3-related increase in FDA activity in one season was attributed to enhanced nitrogen input due to N 2O 5 contamination.