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.
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