2025/03/03 by Changhyeon Kim, Chieri Kubota · 1 voice
Agricultural and Biological Sciences · #Light effects on plants
paper · doi:10.21273/horttech05581-24
openalex publication_date 2025/03/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/26
The light compensation point (LCP) is a key plant photosynthetic parameter and represents the light intensity at which the photosynthetic rate equals the respiration rate, indicating the light level for the null leaf carbon balance. In general, the LCP is calculated from a photosynthetic light response curve (LRC), which characterizes changes in the net photosynthetic rate (P n ) in response to the photosynthetic photon flux density (PPFD; 400–700 nm). However, recent reports highlight a positive contribution of far-red (FR) light (specifically in the range of 700–750 nm) to photosynthesis. FR light is abundant in ecosystems and widely used in indoor crop production, yet its effect on the LCP remains unclear. The objective of this study was to evaluate the effect of FR light (700–750 nm) on the LCP. In this experiment, light conditions with varying FR to extended photosynthetically active radiation [ePAR; 400–750 nm, a revised definition of photosynthetically active radiation (PAR) including FR photons] ratios, representing an abundance of FR light in the light source, were applied during acclimatization and LRC measurements in tomato ( Solanum lycopersicum cv. Maxxiany). Tomato plants were acclimatized under light conditions with 2% or 44% FR-to-ePAR ratios, with the same extended photosynthetic photon flux density (ePPFD; PPFD for ePAR; 400 μmol·m –2 ·s –1 ) in a growth chamber. P n was measured under varying PPFD or ePPFD levels of 2% or 44% FR-to-ePAR ratios. The PPFD- and ePPFD-based LCP were calculated using the photosynthetic parameters estimated from the P n model. Acclimatization under 44% FR light resulted in significantly greater LCPs compared with 2% FR light in both PPFD-based (20.8 ± 4.5 and 18.0 ± 4.5 μmol·m –2 ·s –1 for 44% and 2% FR light, respectively) and ePPFD-based (similarly 27.6 ± 3.6 and 23.9 ± 4.0 μmol·m –2 ·s –1 ) measurements. The higher LCPs under 44% FR light suggest the contribution of FR photons to photosynthesis, compensating for its lower PAR levels. This supports that PPFD-based LCPs are likely underestimated when higher FR photons are present in the light source, as the contribution of FR light to photosynthesis is ignored. These findings emphasize the importance of revision of PAR definition to include FR photons (ePAR), which is essential to obtain accurate LCP values, particularly FR-rich light conditions.