Far-red light is needed for efficient photochemistry and photosynthesis

Abstract

The efficiency of monochromatic light to drive photosynthesis drops rapidly at wavelengths longer than 685nm. The photosynthetic efficiency of these longer wavelengths can be improved by adding shorter wavelength light, a phenomenon known as the Emerson enhancement effect. The reverse effect, the enhancement of photosynthesis under shorter wavelength light by longer wavelengths, however, has not been well studied and is often thought to be insignificant. We quantified the effect of adding far-red light (peak at 735nm) to red/blue or warm-white light on the photosynthetic efficiency of lettuce (Lactuca sativa). Adding far-red light immediately increased quantum yield of photosystem II (Φ) of lettuce by an average of 6.5 and 3.6% under red/blue and warm-white light, respectively. Similar or greater increases in Φ were observed after 20min of exposure to far-red light. This longer-term effect of far-red light on Φ was accompanied by a reduction in non-photochemical quenching of fluorescence (NPQ), indicating that far-red light reduced the dissipation of absorbed light as heat. The increase in Φ and complementary decrease in NPQ is presumably due to preferential excitation of photosystem I (PSI) by far-red light, which leads to faster re-oxidization of the plastoquinone pool. This facilitates reopening of PSII reaction centers, enabling them to use absorbed photons more efficiently. The increase in Φ by far-red light was associated with an increase in net photosynthesis (P). The stimulatory effect of far-red light increased asymptotically with increasing amounts of far-red. Overall, our results show that far-red light can increase the photosynthetic efficiency of shorter wavelength light that over-excites PSII.

Low red/far-red ratio as a signal promotes carbon assimilation of soybean seedlings by increasing the photosynthetic capacity

“…1 and 2) [9]. In addition, the promotive effect of additional Fr radiation on photosynthesis and whole-plant net assimilation was previously reported in lettuce and geranium [12,18]. Together, these results suggested that the high enrichment of Fr light possibly contributed to increased starch and sucrose contents by improving photosynthetic capacity of soybean leaves.…”

“…Plant leaves absorb less amount of Fr light (λ > 700 nm); therefore, it contributes less towards the quantum yield of photosynthesis [17]. However, Zhen and van Iersel [18] reported that Fr light is required for efficient photochemistry and photosynthesis. Similarly, the Fr light of the shade is higher than that of low light, thereby increasing the net photosynthesis rate (P n ) under the same light intensity condition [11], resulting in increased the whole-plant net assimilation [6,9].…”

“…Similarly, the Fr light of the shade is higher than that of low light, thereby increasing the net photosynthesis rate (P n ) under the same light intensity condition [11], resulting in increased the whole-plant net assimilation [6,9]. Typically, a shorter wavelength is used with longer wavelengths to enhance its photosynthetic efficiency, and this overall phenomenon is called the Emerson enhancement effect [18]. The reverse effect, which is the enhancement of the quantum yield of short light wavelength by Fr light (e.g., at low R/Fr ratio) in different light intensity environments, has not received considerable attention.…”

“…The reverse effect, which is the enhancement of the quantum yield of short light wavelength by Fr light (e.g., at low R/Fr ratio) in different light intensity environments, has not received considerable attention. Some studies only indicate that Fr light can increase plant photosynthesis and biomass [6,18]. Therefore, in uncoupling R/Fr ratio from shade, whether low R/Fr ratio (Fr light enrichment) in different light intensity regulates the photomorphogenic process needs further analysis.…”

“…Photosystems I and II (PS I and II, respectively) operate in series to carry out the primary photochemical reactions of photosynthesis [18]. These processes are involved in light absorption and energy and electron transfer, which are carried out by different related proteins [11,19].…”