Raspberries' Year-Round Protective Light Show

By Don Comis
February 27, 2004

Raspberries are playing enough tricks with light to suggest they are likely doing this to hide themselves from insects and deer, as well as protect themselves against disease, ultraviolet rays, oxidation and dehydration in freezing weather, according to a soil scientist with the Agricultural Research Service.

Charles M. Feldhake, at ARS' Appalachian Farming Systems Research Center in Beaver, W.Va., used a special light sphere and fiber optic probe connected to a spectroradiometer to measure light reflected by wild black raspberries and an old variety of red raspberry growing along the edge of a row of scarlet oaks. It's part of Feldhake's research in agroforestry, the science of interspersing livestock and farm crops with trees and shrubs.

Feldhake is studying raspberries as one of many possible "pick-your-own" crops for Appalachian farmers to plant at the edge of trees that might be grown for firewood, for example. He found that the fuzzy "white" undersides of raspberry leaves were highly reflective, about a third as much as a pure-white surface. In deserts, it's the upper sides of plant leaves that normally are reflective, to keep the plant from overheating.

But raspberries grow well under partially shaded, moist conditions, so the light-reflecting fuzziness on the leaves' undersides seems instead designed to hide the plant from insects that expect plant leaves to be green. It also repels water, helping prevent moisture from spreading plant diseases, as well as keeping the leaf stomata free of moisture and open for the gas exchange required for photosynthesis.

The "cane" stems of raspberries turn from green to red in the winter, offering protection against ultraviolet rays and oxidation. A white, waxy coating on the canes should help the plant blend in with snow and hide itself from deer when it is some of the only browsing food above the snow. The cane coating reflected nearly half as much light as a white surface.

ARS is the U.S. Department of Agriculture's chief scientific research agency.