Evolutionary significance of isoprene emission from mosses

Isoprene emission has been documented and characterized from species in all major groups of vascular plants. We report in our survey that isoprene emi ssion is much more common in mosses and ferns than later divergent land pla nts but is absent in liverworts and hornworts. The light and temperature re sponses of isoprene emission from Sphagnum capillifolium (Ehrh.) Hedw. are similar to those of other land plants. Isoprene increases thermotolerance o f S, capillifolium to the same extent seen in higher plants as measured by chlorophyll fluorescence. Sphagnum, species in a northern Wisconsin bog exp erienced large temperature fluctuations similar to those reported in tree c anopies. Since isoprene has been shown to help plants cope with large, rapi d temperature fluctuations, we hypothesize the thermal and correlated dessi cation stress experienced by early land plants provided the selective press ure for the evolution of light-dependent isoprene emission in the ancestors of modern mosses. As plants radiated into different habitats, this capacit y was lost multiple times in favor of other thermal protective mechanisms.