Author
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Feldhake, Charles |
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Submitted to: Sustainable Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/13/2001 Publication Date: 4/26/2002 Citation: FELDHAKE, C.M. BENEFICIAL SPECTRAL CHARACTERISTICS OF RED AND BLACK RASPBERRY PLANTS (RUBUS IDAEUS L.AND RUBUS OCCIDENTALIS L.). SUSTAINABLE AGRICULTURE. 2002. v. 19. p. 65-76. Interpretive Summary: In agroforestry production systems, understory crops must be managed to optimize utilization of a limited amount of light. Red and black raspberry plants are well adapted to partially shaded environments. However, leaf and cane surfaces have visual spectral characteristics that seem anomalous with what is expected under low light conditions. Color measuring instrumentation was used to quantify the light reflecting and absorbing nature of raspberry leaves and canes. This information was used to assess the relative impact of differences in raspberry plant surfaces compared to normal green plant surfaces in low light environments. The results suggest these plants have evolved complex strategies to protect themselves from pests and environmental stresses. The anomalous visual appearance is not likely to substantially impact photosynthesis directly. This work provides insights into characteristics that benefit plants in low light environments sin humid temperate climates. This information will help select appropriat species and cultivars for improving the productivity of agroforestry systems of benefit for small Appalachian farms. This information will benefit small farms with species diverse production systems. It will benefit rural economies by improving design of production systems that increase and diversify small farm income. Technical Abstract: In spite of thriving in relatively low solar radiation environments, some red and black raspberry plant (Rubus idaeus L. and Rubus occidentalis L.) surfaces are highly reflective, both species on leaf abaxial surfaces and black raspberry on cane surfaces. Surface cell color of canes also varies from green to dark red. The objective of this study was to quantify plant spectral characteristics and to assess their potential ecological significance. Reflectance and transmittance were determined using a Li-Cor LI-1800 Spectroradiometer with a fiber optic probe, a regulated light source, and a 1800-12 External Integrating Sphere. Reflected irradiance under natural sunlight was measured using the spectroradiometer with a Li- Cor LI-1800-06 Telescope/Microscope Receptor. Reflectance of abaxial leaf surfaces was 4.3 and 5.3 times greater than adaxial leaf surfaces for red and black raspberry. This amounted to 27 and 29% of possible reflected radiation from a white barium sulfate standard for red and black raspberry respectively. The glaucus coating on black raspberry canes reflected nearly half as much as a barium sulfate standard. The dark red color of surface cane cells was primarily due to higher absorption of green and yellow wavelengths rather than reflection of more red. The variety of spectral strategies employed by these raspberry species suggest a sophisticated system of protection from pests, disease, herbivores, ultraviolet radiation, oxygen free radicals, and high and low moisture conditions. |
