EFFECTS OF SO2 AND O3 ON THE CHEMISTRY AND FDA ACTIVITY OF CONIFEROUSLEAF-LITTER IN AN OPEN-AIR FUMIGATION EXPERIMENT

An open-air fumigation facility, developed for continuous fumigation o f young conifers by SO2 and O3, 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 t o 44 months. Sulphur dioxide treatment consistently increased the rate of removal of base cations from the litter, with the order of sensiti vity of cations to SO2-induced leaching being Mg > Ca > K > Na. The pH of naturally fallen Scots pine needles was reduced by 0.5 units in th e high SO2 treatments. Fluorescein diacetate (FDA) activity and rates of mass loss of naturally-fallen needles were lower in SO2 fumigated p lots than ambient controls. Transplantation experiments showed that th e depression in decomposer activity was caused by exposure of needles to SO2 while still green. Ozone fumigation exerted no effects on the c hemical composition of litter, and an O3-related increase in FDA activ ity in one season was attributed to enhanced nitrogen input due to N2O 5 contamination.