Red Leaf Color as an Indicator of Environmental Stress
Vistas of colorful fall foliage hold tremendous public and media interest, and associated tourism to the Northern Forest is estimated to add billions of dollars to the regional economy each year. This natural spectacle of diverse leaf coloration is based on the physiology of leaf pigments. In addition to its aesthetic value, the biology of one pigment (anthocyanin) may provide insights to how some trees survive environmental stress.
Anthocyanins are red, blue or purple pigments most often seen in flowers and fruits. Although the biochemistry and physiology of chlorophylls (foliar green pigments) are well understood, less is known about anthocyanins - especially their biological roles in autumn leaves. Many stress factors are known to induce anthocyanin synthesis in foliage including UV-B radiation, osmotic stress, drought, low temperature, nutrient deficiency, wounding, pathogen infection and ozone exposure. Recent work on woody species has emphasized the potential value of anthocyanins as a “light screen” that protects the photosynthetic apparatus of senescing leaves and enables prolonged nutrient absorption before leaf abscission. It is also possible that anthocyanins may provide protection from oxidative stress or increase plant cold hardiness and drought resistance. Still, the specific causes and consequences of anthocyanin - and how this relates to overall tree and forest health - remains unclear.
Our research team is 1) identifying factors that stimulate anthocyanin biosynthesis during autumn and in response to environmental stress, and 2) evaluating the possible ecological benefits of anthocyanin production in senescing leaves.
Our past research specifically evaluated factors, such as mineral nutrition, carbohydrate concentrations, and water content that influence leaf color development in sugar maple (Acer saccharum) leaves during autumn. We found that nutrient limitations (particularly nitrogen deficiency) and associated carbohydrate buildups may provide the biochemical triggers, energy and carbohydrate building blocks needed for the production of anthocyanins. We recently expanded our studies to include experimental manipulations to evaluate the possible connections between autumnal anthocyanin expression and stress response. To best simulate native environmental stresses that may cause disruptions in sugar mobilization via phloem transport (e.g., low temperatures and wounding), we physically girdled branches of mature sugar maple trees. Branch girdling significantly increased foliar sugar concentrations and anthocyanin expression. The same basic physiological connections are similar to reports of red leaf coloration found in branch wounding and insect and fungal damage. Another of our recent studies provides the first anatomical evidence in support of the hypothesis that anthocyanin accumulation may benefit trees by extending foliar nutrient resorption from senescing leaves and into woody storage sites.
We hope to gain a detailed understanding of the linkage between environmental stress exposures and anthocyanin production which may provide better insight into the role(s) anthocyanins play in plant stress response systems. This knowledge is particularly important as invasive pests, climate change and sustained air pollution threaten the overall health of Northern Forest tree species.
Archetti, M.; Doring, T.F.; Hagen, S.B.; Hughes, N.M.; Leather, S.R.; Lee, D.W.; Lev-Yadun, S.; Manetas, Y.; Ougham, H.J.; Schaberg, P.G.; Thomas, H. 2008. Unravelling the evolution of autumn colours: an interdisciplinary approach. Trends in Ecology and Evolution 24:166-173.
Murakami, P.F., Schaberg P.G.; Shane, J.B. 2008. Stem girdling manipulates leaf sugar concentrations and red expression in sugar maple trees during autumn. Tree Physiology 28:1467-1473.
Schaberg, P.G.; Murakami, P.F.; Turner, M.R.; Heitz, H.K.; Hawley, G.J.. 2008. Associations of red coloration with senescence of sugar maple leaves in autumn. Trees 22:573-578.
Murakami, P.F.; Turner, M.R.; van den Berg, A.K.; Schaberg, P.G. 2005. An instructional guide for leaf color analysis using digital imaging software. Gen. Tech. Rep. NE-327. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 33 p.
Schaberg, P.G.; van den Berg, A.K.; Murakami, P.F.; Shane, J.B.; Donnelly, J.R. 2003. Factors influencing red expression in autumn foliage of sugar maple trees. Tree Physiology 23:325-333.
- Paul G. Schaberg, US Forest Service - Northern Research Station - Research Plant Physiologist
- Paula F. Murakami, US Forest Service - Northern Research Station - Research Associate
- John B. Shane, The University of Vermont - Senior Researcher
- Gary J. Hawley, The University of Vermont – Senior Researcher
Last Modified: 07/24/2009