Spectral irradiance available for turfgrass growth in sun and shade

The spectral quality of solar radiance affects plant growth and development . The purpose of this study was to assess the spectral quality of deciduous shade, coniferous shade, building shade, and full sun in a natural environ ment common to turfgrass growth throughout a day and throughout a growing s eason. A spectroradiometer was used to acquire solar spectra in these four environments. Acquisitions were made on an hourly basis from 0730 to 1930 h , biweekly, from vernal equinox to autumnal equinox at The Ohio Turfgrass F oundation Research and Educational Center and from 10 April to 1 July 1997 at The Ohio State University campus. Data were tested for variation in spec tral quality between morning hours and afternoon hours in full sun and amon g full sun and deciduous, coniferons, and building shade. Results indicated that changes in spectral quality occurred between morning and afternoon pe riods in full sun, but total (red + blue) photosynthetically active irradia nce was not affected, Measurements indicated that a deciduous tree and a co nifer tree filtered significantly more high activity (red + blue) quanta th an a building. Blue irradiance relative to total irradiance increased and r ed irradiance decreased with increasing shade density. Significant differen ces were detected between full sun, tree shade, and building shade for blue photoreceptor potential (blue photon flux/far-red photon flux) and phytoch rome potential (red photon flux/far-red photon nu). Results indicated that relationships among blue, red, and far-red irradiance that influence many p lant responses were affected by both shade source and shade density.