Sensitivity of Seven Diverse Species to Blue and Green Light: Interactions with Photon Flux

Abstract

Despite decades of research, the effects of spectral quality on plant growth, and development are not well understood. Much of our current understanding comes from studies with daily integrated light levels that are less than 10% of summer sunlight thus making it difficult to characterize interactions between light quality and quantity. 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; with a daily light integral of 11.5 and 29 mol m-2 d-1) on growth (dry mass), leaf expansion, stem and petiole elongation, and whole-plant net assimilation of seven diverse plant species. The treatments included cool, neutral, and warm white LEDs, and combinations of blue, green and/or red LEDs. At the higher PPF (500), increasing blue light in increments from 11 to 28% reduced growth 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 0 to 30% had a relatively small effect on growth, leaf area and net assimilation at either low or high PPF. Surprisingly, growth 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.

Toward an optimal spectral quality for plant growth and development: the importance of radiation capture

“…Contrary to several reports on significant green light effects on growth (both increases and decreases), Snowden et al (2016) found no consistent effect of green light among species on growth or photosynthetic efficiency. Nelson and Bugbee (2014) reported the photosynthetic (400-700 nm) photon efficiency and photon distribution pattern of multiple models of fixtures from four lighting technologies.…”

“…These results suggest that the effect of blue light on reducing leaf area and radiation interception was the underlying cause of the reduction in growth. Snowden et al (2016) also found that increasing blue light had a greater effect at PPF 500 than at 200 for cucumbers, radishes and peppers, but there was no significant interactions between PPF and blue light fraction for the other four species.…”

“…A tall plant without branches might have the same growth (dry mass) as a short highly branched plant, but they have developed differently. Although wheat, and possibly all grasses, appears to have minimal sensitivity to spectral quality (Dougher and Bugbee, 2001); tomatoes are exquisitely sensitive; cucumbers, radishes and peppers have intermediate sensitivity; soybeans and lettuce have low sensitivity (Snowden et al 2016). Blue light can alter secondary metabolism and these compounds provide protection from biotic and abiotic challenges.…”

“…In a comprehensive study with seven species, Snowden et al (2016) studied the effect of blue and green light fractions at PPFs of 200 and 500 umol m -2 s -1 . In contrast to some previous studies, growth (total dry mass) of three of the seven species was not reduced by a treatment with 93 % green light compared to the broad spectrum, multi-wavelength treatments.…”

Relation between Changes in Photosynthetic Rate and Changes in Canopy Level Chlorophyll Fluorescence Generated by Light Excitation of Different Led Colours in Various Background Light

“…", is still not easy to answer, since it depends on plant species, the ontogenesis stage, surrounding environment and how "maximal productivity" is defined. As an example, Snowden et al [5] measured the sensitivity to blue light for a number of species including cucumber and lettuce. Increasing the amount of blue light did not significantly affect plant growth for lettuce.…”