Document Type

Article

Publication Date

Winter 2-2016

Abstract

The effects of spectral quality on growth, carbon-partitioning and whole-plant net assimilation remain poorly understood. Much of the research data is at light levels less than 10% of summer sunlight so interactions between light quality and quantity are poorly characterized.Several studies have reported that growth is increased under fluorescent lamps compared to mixtures of wavelengths from LEDs. Conclusions regarding the effect of green light fraction range from detrimental to beneficial. Here we report the effects of eight blue and green light fractions at two photosynthetic photon fluxes (PPF; 200 and 500 µmol m-2 s-1; daily light integral, 11.5 and 29 mol m-2 d-1) on growth, leaf expansion, stem and petiole elongation, and whole-plant net assimilation of seven diverse species. The treatments included cool, neutral, and warm white LEDs, and combinations of blue, green and red LEDs. At the higher PPF (500),increasing blue light in increments from 11 to 28% reduced growth (dry mass) in tomato,cucumber, and pepper by 22, 26, and 14% respectively, but there was no statistically significant effect on radish, soybean, lettuce or wheat. At the lower PPF (200), increasing blue light reduced growth only in tomato (41%). The effects of blue light on growth were mediated by changes in leaf area and radiation capture, with minimal effects on whole-plant net-assimilation. In contrast to the significant effects of blue light, increasing green light in increments from zero to 30% had a relatively small effect on growth, leaf area or net assimilation at either low or high PPF.Surprisingly, growth (dry mass) of three of the seven species was not reduced by a treatment with 93% green light compared to the broad spectrum treatments. Collectively, these results are consistent with a shade avoidance response associated with either low blue or high green light fractions.

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