Response of SO2-fumigated Pinus resinosa seedlings to postfuniigation temperature

Abstract

Effects of postfumigation temperature on SO2-fumigated seedlings of red pine (Pinus resinosa Ait.) were studied. Seedlings were fumigated with either 0.2 ppm SO2 for 91 h or with 0.5 ppm SO2 for 30 h. Seedling injury was much greater at the higher SO2 concentration. At the lower SO2 concentration, only root weight of fumigated seedlings was affected, and it was about 20% less than that of unfumigated controls after 6 weeks at 12, 22, or 32 °C; there was no interaction between SO2 treatment and postfumigation temperature on growth rate. Postfumigation growth was reduced more by the higher concentration of SO2. Significant interaction between SO2 and postfumigation temperature occurred, with growth of roots, primary needles, and secondary needles being reduced most at 12 °C. At higher postfumigation temperatures, SO2-fumigated seedlings recovered (partially) and initiated secondary needles, thereby providing a new source of photosynthate and further reducing growth inhibition. But at 12 °C, shoot growth was slow and injured needle tissue was not replaced; hence the dry weight of roots of plants fumigated at the higher SO2 concentration was <30% of that of controls after 6 weeks. Interpretation of effects of fumigation temperature on SO2 toxicity should also consider influences of postfumigation temperature regimes.