Editing Taiga (section)

===Pollution===
The effect of [[Sulfur dioxide|sulphur dioxide]] on woody boreal forest species was investigated by Addison et al. (1984),<ref name="add">Addison, P.A.; Malhotra, S.S.; Khan, A.A. 1984. "Effect of sulfur dioxide on woody boreal forest species grown on native soils and tailings". ''J. Environ. Qual.'' 13(3):333–36.</ref> who exposed plants growing on native soils and tailings to 15.2 μmol/m<sup>3</sup> (0.34 ppm) of SO<sub>2</sub> on CO<sub>2</sub> assimilation rate (NAR). The Canadian maximum acceptable limit for atmospheric SO<sub>2</sub> is 0.34 ppm. Fumigation with SO<sub>2</sub> significantly reduced NAR in all species and produced visible symptoms of injury in 2–20 days. The decrease in NAR of deciduous species (trembling aspen [''Populus tremuloides''], willow [''Salix''], green alder [''Alnus viridis''], and white birch [''Betula papyrifera'']) was significantly more rapid than of [[Pinophyta|conifers]] (white spruce, black spruce [''Picea mariana''], and jack pine [''Pinus banksiana'']) or an evergreen [[angiosperm]] (Labrador tea) growing on a fertilized Brunisol.

These metabolic and visible injury responses seemed to be related to the differences in S uptake owing in part to higher gas exchange rates for [[deciduous]] species than for [[Pinophyta|conifers]]. Conifers growing in [[oil sands]] tailings responded to SO<sub>2</sub> with a significantly more rapid decrease in NAR compared with those growing in the Brunisol, perhaps because of predisposing toxic material in the tailings. However, [[Sulfur|sulphur]] uptake and visible symptom development did not differ between conifers growing on the 2 substrates.

Acidification of precipitation by anthropogenic, acid-forming emissions has been associated with damage to vegetation and reduced forest productivity, but 2-year-old white spruce that were subjected to simulated [[acid rain]] (at [[PH indicator|pH]] 4.6, 3.6, and 2.6) applied weekly for 7 weeks incurred no statistically significant (P 0.05) reduction in growth during the experiment compared with the background control (pH 5.6) (Abouguendia and Baschak 1987).<ref name="abou">Abouguendia, Z.M.; Baschak, L.A. 1987. "Response of two western Canadian conifers to simulated acidic precipitation". ''Water, Air and Soil Pollution'' 33:15–22.</ref> However, symptoms of injury were observed in all treatments, the number of plants and the number of needles affected increased with increasing rain acidity and with time. Scherbatskoy and Klein (1983)<ref name="scher">Scherbatskoy, T.; Klein, R.M. 1983. "Response of spruce Picea glauca and birch Betula alleghaniensis foliage to leaching by acidic mists". ''J. Environ. Qual.'' 12:189–95.</ref> found no significant effect of [[chlorophyll]] concentration in [[white spruce]] at pH 4.3 and 2.8, but Abouguendia and Baschak (1987)<ref name="abou" /> found a significant reduction in white spruce at pH 2.6, while the foliar sulphur content significantly greater at pH 2.6 than any of the other treatments.