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The Effects of SO₂ on in vitro Forest Tree Pollen Germination and Tube Elongation¹

ABSTRACT

The 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.

Key Words: Populus deltoides • Pinus resinosa • Pinus nigra • Picea pungens

¹ Contribution from the Department of Forestry, University of Wisconsin, Madison, 53706. Research supported by the School of Natural Resources, College of Agriculture and Life Sciences, University of Wisconsin; Hatch Project 1595 (Air Pollution Effects on Forest Trees); and by a grant from the Wisconsin Power and Light Co., the Madison Gas and Electric Co., and the Wisconsin Public Service Co.

² Research Assistant and Professor of Forestry, respectively.

Received for publication January 17, 1974.