ADAPTATION TO METAL-CONTAMINATED SOILS IN POPULATIONS OF THE MOSS, CERATODON PURPUREUS - VEGETATIVE GROWTH AND REPRODUCTIVE EXPRESSION

Many observations suggest that morphological evolution occurs slowly i n bryophytes, and this has been suggested to reflect low genetic diver sity within species. Isozyme studies, however, stand in apparent contr ast and have shown that bryophytes can contain high levels of genetic variability within and among populations. In light of this conflict, w e tested the potential of the moss, Ceratodon purpureus, to undergo ad aptive change (i.e., ecotypic differentiation) in response to soils th at have been contaminated with high levels of metals for 90 years by m easuring gametophytic growth and reproductive expression under experim ental conditions. Variation in protonemal growth in sterile culture in dicates that plants from one population growing on contaminated soil n ear a smelter are significantly more tolerant of zinc, cadmium, and le ad than plants from uncontaminated sites. Results from a common garden experiment, in which plants were grown on soil from the smelter site, indicate that plants from near the smelter are significantly more tol erant of contaminated soils than plants from uncontaminated sites for vegetative growth. The same experiment suggests that plants from the s melter site are also more tolerant in terms of gametangial production (although we could not test this statistically). Our results demonstra te that C. purpureus has been able to undergo relatively rapid evoluti on in response to strong selective pressures.