Abstract
The recent development of light-emitting diodes (LEDs) and their application in modern horticulture stimulated studies demonstrating that additional far-red (FR) radiation (700–800 nm) increases plant dry mass. This effect of FR has been explained by improved photosynthesis and/or plant architecture. However, the genotypic variation in this response is largely unknown. Here, we aim to explore and explain the genotypic variation in growth responses to additional FR. We expected the genotypic variation in the responses of plant dry mass to additional FR. Further, we hypothesized that a significant improvement of both net assimilation rate (NAR) and leaf area ratio (LAR) is responsible for a strong dry mass increase under additional FR, while some genotypes respond only marginally or even negatively in NAR or LAR under FR, thus resulting in a weak FR effect on plant dry mass. To test these hypotheses, we grew 33 different tomato genotypes for 21 days with 0, 25, or 100 μmol m–2 s–1 of FR added to a common white + red LED background lighting of 150 μmol m–2 s–1. Genotypes responded similarly with respect to plant height, stem dry mass, and shoot:root ratio; i.e., they all increased with increasing FR. However, the response of total plant dry mass varied among genotypes. We categorized the genotypes into three groups (strongly, moderately, and weakly responding groups) based on their relative response in total plant dry mass to FR. Growth component analysis revealed that the strongly responding genotypes increased strongly in NAR rather than LAR. The weakly responding genotypes, however, showed a substantial increase in LAR but not NAR. The increase in LAR was due to the increase in specific leaf area. Leaf mass fraction, which is the other component of LAR, decreased with FR and did not differ between groups. In conclusion, tomato genotypes that increased strongly in NAR in response to FR were able to achieve a more substantial increase in dry mass than did other genotypes. This is the first study to explain the differences in growth responses of a large number of tomato genotypes toward FR in their light environment.
Highlights
Far-red (FR) radiation (700–800 nm) is an important light signal perceived by plants via the phytochrome photoreceptor family
58% of the genotypes showed a positive response under 25 μmol m−2 s−1 of FR, and this percentage increased to 70% under 100 μmol m−2 s−1 of FR
Our result suggests that when grown under additional FR, tomato plants are not likely to be able to increase net assimilation rate (NAR) and leaf area ratio (LAR) simultaneously, and that the genotypes with a strong increase in NAR under FR allowed them to achieve a stronger increase in relative growth rate (RGR) than did other genotypes
Summary
Far-red (FR) radiation (700–800 nm) is an important light signal perceived by plants via the phytochrome photoreceptor family. A low R:FR ratio causes the equilibrium between the two isoforms of phytochromes to shift toward Pr, resulting in a set of morphological and physiological changes collectively known as the shade-avoidance syndrome (SAS). Plant photosynthesis is driven by photosynthetically active radiation (PAR; 400–700 nm). When added to PAR, FR radiation may increase yield (Ji et al, 2019, 2020) and total plant biomass production (Li and Kubota, 2009; Park and Runkle, 2017; Zhen and van Iersel, 2017). Several recent studies revisited this concept and proposed the reverse interpretation: FR radiation enhances the quantum yield of PAR (Zhen and van Iersel, 2017). Zhen and Bugbee (2020) demonstrated in an experiment with 14 species of both C3 and C4 crops that FR can be as efficient in driving photosynthesis as PAR, not by itself but when provided in addition to PAR
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
