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Direct Effects of Simulated Acid Rain on Sexual Reproduction in Corn

Air Quality Research Program, North Carolina State Univ., 1509 Varsity Dr., Box 7632, Raleigh, NC 27606.

^* Corresponding author.

ABSTRACT

The process of sexual reproduction in flowering plants often exposes pollen grains to the environment and the potential effects of atmospheric deposition. Experiments were designed to determine whether simulated acid rain treatments just before or after pollination could adversely influence reproductive processes and seed set in corn (Zea mays L.). Container-grown corn with sexually mature tassels and ears were exposed once to simulated rain at four pH levels for 1 h, beginning 1 h after artificial pollination or ending 10 min before artificial pollination. The single, artificial pollination deposited an average of 85 pollen grains per silk. Simulated rain treatment at pH 4.5, 3.5, or 2.5 after pollination reduced the percentage seed set of treated ears 7, 29, and 34%, respectively, as compared with pH 5.5. Simulated rain at pH 5.5 after pollination reduced seed set 24% as compared with no-rain controls. The pH of simulated rain applied before pollination did not affect seed set, and pH 5.5 rain applied before pollination had no effects on seed set compared to no-rain controls. Microscopic observations indicated that pollen germination and pollen tube penetration of the silk were completed by the time the rain treatments began 1 h after pollination. This infers that simulated acid rain influenced pollen tubes after they entered the silks. These results suggest that plant sexual reproduction could be adversely affected by acidic precipitation at pH levels observed for rain events in eastern North America.

Cooperative investigations of the Dep. of Botany and the USDA-ARS Air Quality Research Program, North Carolina State Univ. Paper no. 11501 of the Journal Series of the North Carolina Agric. Res. Service. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Service of the products named, nor criticism of similar ones not mentioned.

Received for publication April 27, 1988.