Effects of acidity on invitro pollen germination and tube elongation in four hardwood species

The effects of media acidity on pollen germination and tube elongation of four northeastern tree species, flowering dogwood (Cornusflorida L.), black birch (Betulalenta L.), yellow birch (Betulaalleghaniensis Britton), and sugar maple (Acersaccharum Marsh.), were investigated. Pollen was collected and germinated in growth media that were acidified to pH values ranging from 5.0 to 2.6. Pollen of all four species were affected by acidification of the germination medium to below pH 4.2. At pH 3.0 and 2.6 no pollen germinated in any species. Betwee pH values of 4.2 and 3.4, germination was reduced by more than 50% from that at pH 5.0. Mean tube length was reduced at the lowest pH at which germination occurred. The pH of the growth medium increased during pollen germination to at least 5.2 when initial pH values were 3.8 and above. These results suggest that media acidity can influence pollen germination and, consequently, acid rain, which now occurs in eastern North America, may affect reproductive processes in northern hardwood forests.