The influence of plant spacing and row orientation on spectral distribution of light received by growing soybean (Gykine max [L.] Meff.) plants was measured under field conditions. Light absorption, reflection and transnission of individual leaves showed that most of the blue and red was absorbed while most of the far-red was either reflected or transmitted. Plants growing in the field received different ratios of farred relative to red, depending on nearness and/or orientation of other vegetation. Plants grown in close-spaced rows, or high population densities, received higher far-red/red ratios than did those grown in wide rows, or sparse populations. Heliotropic movements of the leaves also contributed to the far-red reflection patterns associated with row orientation. Under field conditions, differences in far-red/red ratios associated with nearness of competing vegetation became more pronounced with low solar angle near the end of the day. Plants exposed to far-red for 5 minutes at the end of each day in controlled environments, and those grown in closespaced rows in the field, developed longer internodes and fewer branches. Red, far-red photoreversibility in the controlled environment study indicated involvement of phytochrome. Dry matter partitioning among plant components in the field was related to far-red/red light ratio received during growth and development.Plants of the same genotype frequently differ in phenotypic development when grown in crowded relative to sparse populations. It is apparent that each plant is genetically programmed for a number of alternate developmental patterns and that expression depends on the environmental combination that exists during plant growth and development (1,9,17 Spectral distributions of incoming radiation received by leaves near the top of the canopies were measured at 5-nm intervals between 400 and 850 nm with a LiCor2 Spectroradiometer LI-1800 equipped with a remote light collector on a fiber optic probe. A reference spectrum was obtained by measuring direct solar radiation. Spectral irradiances at 735 and 645 nm were used to calculate the FR/R ratios. These values were used because they approach the peaks for phytochrome action spectra in green plants; 645
Shifts in spectral distribution of light were determined within and below a canopy of field-grown burley tobacco (Nicotiana tabacum L cv. Burley 21). The Radiation measurements presented in this report were taken at about 1300 hours on September 1, 1967, a cloudless day. Transmission of sunlight through individual fully expanded tobacco leaves was tested with the same instruments on the same day.CONTROLLED ENVIRONMENT STUDY Plant Materials. The tobacco (cv. Burley 21) seedlings were started and grown in vermiculite for about 8 weeks under 14-hr, 1600-ft-c photoperiods at 28 C. During the starting period all plants were subirrigated daily with Hoagland's nutrient solution 1 (9). Roots were washed and cut back to a 1 cm "brush," and all leaves longer than 5 cm were removed at the beginning of the experimental period. Plants were placed about 30 cm apart in plastic pans, and roots were suspended in aerated nutrient solution (9) during the treatment period.Treatments. Throughout the controlled environment experiment, all plants were kept in the same growth environment except during the daily irradiations with red or far red light.The chamber was kept at 25 C, and the plants received 8-hr, 2200-ft-c photoperiods from cool-white fluorescent lamps. Red light (360 uw/cm' over the wavelength band of 600-700 nm) was obtained by filtering radiation from cool-white fluorescent lamps through two layers of red cellophane. Far red (360 ,w/cm' over the region of 700-770 nm) was obtained from internal reflector incandescent-filament flood lamps through two layers of red and two layers of dark blue cellophane. Red and far red irradiations were applied for 5 min each day, at 775 www.plantphysiol.org on May 10, 2018 -Published by Downloaded from
Allocation of photosynthate among leaves, stems, and roots is critical in seedling establishment. Corn (Zea mays L.) seedlings were grown in different spacing patterns in a field and with different reflected far‐red (FR) to red (R) light ratios to test the effects of a modified FR/R ratio on photoassimilate allocation. Green leaves absorbed most of the R and reflected much of the FR. Therefore, close‐spaced plants received more reflected FR and higher FR/R ratios. Seedlings that received the higher FRJR ratios developed longer and narrower leaves, longer stems, and less massive roots. Stem elongation was an early response to increased FR/R ratio even though fight did not impinge directly on the stems, which were initially at or below the soil surface and covered by several layers of leaves. Row orientation did not significantly alter FR/R ratio or seedling morphology because corn leaves are not heliotropic and did not function as directional FR reflectors, as was observed for soybean [Glycine max (L.) Merr.] in a previous study. An increase in the FR/R ratio reflected up to seedlings from the soil surface also resulted in increased shoot size and shoot/root biomass ratio. Early morphological responses of corn seedlings to FR/R ratio in reflected light are relevant to seedling establishment and are not dependent on the cause of the altered ratio.
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