A study was carried out on the influence of 15.2 µmol m–3 (0.34 ppm) (Canadian maximum acceptable limit) of SO2 on net CO2 assimilation rate (NAR) and visible symptom development of several boreal forest woody species. Fumigation with SO2 significantly reduced NAR in all species and produced visible symptoms of injury in 2 to 20 d. The decrease in NAR of deciduous species {aspen (Populus tremuloides Michx.), willow (Salix sp.), green alder [Alnus crispa (Ait.) Parsh], and paper birch (Betula papyrifera Marsh)} was significantly more rapid than of conifers { jack pine (Pinus banksiana Lamb.), white spruce [Picea glauca (Moench) Voss], and black spruce [P. mariana (Mill.) BSP]} or an evergreen angiosperm [Labrador tea (Ledum groenlandicum Oeder)] when grown on a fertilized Brunisol. cases did not appear until NAR had decreased considerably. The response of these metabolic and visible responses appeared to be related to differences in S uptake owing in part to higher gas exchange rates for deciduous species than for conifers.

Conifers growing in oil sands tailings responded to SO2 with a significantly more rapid decrease in NAR as compared with those growing in the Brunisol. Because both soils were fertilized, nutrient status was ruled out as a cause. It is suggested that the conifers obtained from the railings dike were predisposed to SO2 fumigation by either the presence of toxic material in the tailings sand or their history of exposure to moderate levels of SO2. Sulfur uptake and visible symptom development were not different on tailings as compared with the Brunisol.