The Effects of SO2 on in vitro Forest Tree Pollen Germination and Tube Elongation

Abstract

AbstractThe effects of SO2 on in vitro pollen germination and tube elongation were examined for Populus deltoides (Bartr.), Pinus resinosa (Ait.), Pinus nigra (Arnold), and Picea pungens (Engelm.). Comparisons were made between pollen fumigated in a dry condition and then placed on the germinating media, and moist pollen fumigated while on the germinating media.Moist P. deltoides pollen germination was significantly reduced at SO2 concentrations of 0.75 ppm and above. Populus deltoides pollen tube elongation was more sensitive to SO2 exposure and highly significant decreases in tube length occurred at 0.30 ppm for 4 hours. Tube elongation decreased linearly with increases in SO2 concentration. Frequent bursting of pollen tubes occurred at SO2 concentrations greater than or equal to 0.3 ppm for 4 hours.Exposure to SO2 caused similar effects on pollen germination and tube elongation for Pinus resinosa, Pinus nigra, and Picea pungens. Moist pollen was far more sensitive than dry pollen to SO2 exposure. A 4‐hour exposure to 1.4 ppm SO2 severely restricted moist pollen germination and tube elongation of the three conifer species. However, a similar exposure to 10 ppm SO2 had no effect on dry pollen of the three species.Absorption of SO2 resulted in an acidification of the germination media. Germination trials on acidified media indicated that the resultant acidification could account for much of the reduced germination and tube elongation in P. deltoides but could not adequately explain the reduced conifer pollen germination and tube elongation.