Fall leaf color research could make it possible to predict timing, intensity, and location of fall color
Transitions of leaf color from the greens of the growing season to the mosaic of colors in autumn are a wonder that drive billions of dollars in tourism in each year. The biology behind the fading of green chlorophyll pigments that reveal underlying yellow carotenoid pigments is well known, but interpreting the ecology behind the production of anthocyanin, a red pigment, is problematic. Why use precious sugars to build new pigments in senescing leaves? One reason is that anthocyanins may protect leaves from stress and provide them more time to reabsorb precious resources for later use. But what stress is so prevalent that it would account for widespread expression in the fall? Forest Service scientists proposed that autumnal low temperatures, slow branch sugar transport, and increased leaf sugar concentrations trigger anthocyanin production. They tested this proposal using a unique refrigeration system that cooled branches in a sugar maple tree and induced a two- to nine-fold increase in leaf sugar and anthocyanin concentrations. Although the experiment was conducted at the branch-level, the same response could explain landscape-level variations in anthocyanin displays and help scientists and managers better predict the timing, intensity, and location of color displays cherished by the public.