ACIDIC FOG AND TEMPERATURE EFFECTS ON STIGMATIC RECEPTIVITY IN 2 BIRCH SPECIES

Factorial assays were performed to determine the effects of simulated acid fog (SAF) and temperature on stigmatic receptivity in two birch s pecies. Excised reproductive branches were sampled from representative individuals of mountain paper birch (Betula cordifolia Regel.) and pa per birch (Betula papyrifera Marsh.) in populations adjacent to the Ba y of Fundy, New Brunswick, Canada. Since 1979 these trees have exhibit ed branch dieback in association with abnormal foliar browning symptom s. This browning has been linked with acidity and nitrate deposited by fog, which is frequent in the area. In general, experimental results indicated that pollen germination increased with temperature, but pH e ffects were less obvious. Similarly, pollen tube growth responded posi tively to temperature and was little affected by fog acidity. ANOVA te sts indicated a significant difference (P < 0.05) between species in t heir pollen germination response only at 12-degrees-C, and not at the other three temperatures tested. For pollen tube growth, significant d ifferences between species (P < 0.05) were demonstrated at 12 and 22-d egrees-C. A significant pH effect was demonstrated at 27-degrees-C for germination, while pH effects on tube growth were significant at 27 a nd 12-degrees-C (P < 0.01). A response surface regression analysis ind icated that acidity significantly affected pollen germination in mount ain paper birch (P < 0.001) but not in paper birch. Temperature was no t a significant factor for in vivo pollen germination in either specie s. For pollen tube growth, however, temperature was more important tha n pH and produced highly significant effects in both species (P < 0.00 1). Acidity was also a significant factor in pollen tube growth for pa per birch.