Effects of photosynthetic photon flux density, frequency, duty ratio, and their interactions on net photosynthetic rate of cos lettuce leaves under pulsed light: explanation based on photosynthetic-intermediate pool dynamics

Abstract

Square-wave pulsed light is characterized by three parameters, namely average photosynthetic photon flux density (PPFD), pulsed-light frequency, and duty ratio (the ratio of light-period duration to that of the light-dark cycle). In addition, the light-period PPFD is determined by the averaged PPFD and duty ratio. We investigated the effects of these parameters and their interactions on net photosynthetic rate (P ) of cos lettuce leaves for every combination of parameters. Averaged PPFD values were 0-500 µmol m s. Frequency values were 0.1-1000 Hz. White LED arrays were used as the light source. Every parameter affected P and interactions between parameters were observed for all combinations. The P under pulsed light was lower than that measured under continuous light of the same averaged PPFD, and this difference was enhanced with decreasing frequency and increasing light-period PPFD. A mechanistic model was constructed to estimate the amount of stored photosynthetic intermediates over time under pulsed light. The results indicated that all effects of parameters and their interactions on P were explainable by consideration of the dynamics of accumulation and consumption of photosynthetic intermediates.

Down-Regulation of Photosynthetic Electron Transport and Decline in CO2 Assimilation under Low Frequencies of Pulsed Lights

“…under intermittent lights, they deduced that at the end of the light period, the photochemical reactions cease immediately but the biochemical reactions continue until the photochemical products are consumed by the biochemical reactions, with no other reactions possible until further illumination. This principle underlies the recent kinetic model introduced by Jishi et al [9,11] explaining the relation between net photosynthetic rates Pn of cos lettuce leaves and the characteristics of idea that the oxidation of PQH 2 by Cyt b 6 f limits the steady-state rate of LEF, and that this oxidation has a first-order dependence on PQH 2 [35]. Thus, the conductance (the inverse of resistance) to LEF at Cyt b 6 f can be obtained by the ratio of the rate of LEF over the redox state of the PQ pool estimated by the "1-qL" parameter [36].…”

Cos lettuce growth under pulsed light generated with full-wave rectification of 50 Hz sine-wave alternating-current power

“…However, NPR declination has been reported at frequencies below 100 Hz ( Jishi et al, 2012). The reason for the reduced photosynthetic efficiency has been explained previously in that photosynthetic intermediates are saturated during the long light period and a greater proportion of the absorbed light energy is dissipated as heat ( Tennessen et al, 1995;Jishi et al, 2018). Pulsed light with lower frequencies risks a smaller NPR ( Jishi et al, 2015).…”

The Effect Mechanism and Model Optimization of Pulsed Light Dark Duration on Lettuce

“…A photosynthetic intermediate buffer pool (PIs pool) exists in leaves, which can accumulate a certain amount of photosynthetic intermediate during the application of the light and maintains a continued carbon assimilation process when the light stops. However, the assimilation rate will gradually decrease with time, which may be related to the consumption and regenerated of the RuBP (Ribulose-1,5-bisphosphate), ATP (Adenosine triphosphate) and NADPH (Nicotinamide adenine dinucleotide phosphate) supplies [33][34][35].…”