Greenhouse-grown crops, like tomato, are ever more important, but scientists are still working on the best supplemental light formula to support growth. In an article recently published in the Annals of Botany, Lazzarin and Dupont et al have found for the first time that far-red light is beneficial to photosynthesis in tomato plants, but the effects are complicated by the intensity of light used.
Historically, the definition of photosynthetically active radiation (PAR) excludes far-red light because rates of photosynthesis decline in light longer than 700 nm in wavelength. Typically, 400-700 nm is considered the optimal range for photosynthesis, and lights in this range are used in production. However, plants grown in sunlight are naturally exposed to far-red light, and so scientists such as Lazzarin and Dupont et al have set out to empirically test whether far-red light holds any benefits to growth.
According to Lazzarin & Dupont et al their “study is the first to quantify the impact of short-term removal of far-red [light] in plants grown with a severely reduced amount of far-red [light] in the solar irradiance compared with plants grown with normal amounts of far-red.”
Lazzarin & Dupont et al grew tomato plants under artificial solar light conditions with either severely reduced or normal, sun-like levels of far-red light and found that tomato plants lacking exposure to far-red light had shorter stems and fewer leaves. The leaves were also smaller and darker than normal. Furthermore, the leaves and stems displayed purplish discolorations, likely due to increased anthocyanin, a molecule known to play a role in light absorption in photosynthesis.
When they measured photosynthesis, Lazzarin & Dupont et al found that the removal of far-red light at low light intensity had a negative impact on whole-plant photosynthesis, reducing plant and leaf carbon assimilation rates. No effect was seen at high light intensity.
Lazzarin & Dupont et al suggest that “The similarity in whole-plant photosynthetic rates [at high light intensity] can be explained by the higher photosynthetic rates of the individual leaves, which compensated for the reduction in leaf area in SUN(FR−)- compared with SUN-grown plants.” This explanation is based on individual leaf measurements of photosynthesis, which showed that the upper and lower leaves of the far-red restricted plants had higher photosynthetic rates than those exposed to normal levels of far-red light. Thus, the plants exposed to restricted far-red light at high light intensity were able to compensate for having fewer and smaller leaves. However, at low light intensity, the plants were not able to compensate for the loss of far-red light, and whole-plant photosynthesis was reduced.
Based on these data, Lazzarin & Dupont et al conclude that “in young plants, the presence of far-red [light] in the solar irradiance increases whole-plant photosynthesis in tomato, but only at low light intensity.”
READ THE PAPER
Lazzarin, M., Dupont, K., van Ieperen, W., Marcelis, L.F.M. and Driever, S.M. (2025) ‘Far-red light effects on plant photosynthesis: from short-term enhancements to long-term effects of artificial solar light’, Annals of Botany, 135(3), pp. 589-602. https://doi.org/10.1093/aob/mcae104
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