| In the 21 st century, facing the food crisis caused by global population growth, modern photosynthetic physiology research focused on how to improve the photosynthetic rate of plant leaves, improve light utilization efficiency and efficient operation of photosynthetic apparatus. Improving photosynthetic efficiency of crop became the core of the Second Green Revolution, and its potential mainly focused on the stage of carbon assimilation. In previous studies of our laboratory, the dynamic response of photosynthetic apparatus in tomato leaf had been studied with light intensity step and anti-step change. On the basis,tomato leaf was used to carry out the experiment. With illumination of tomato leaf by different pulsed light frequencies、duty cycles、pulsed photon flux density and high-low intensity pulsed light from light-emitting diodes(wavelength 625 nm), the dynamic response characteristics of photosynthetic apparatus were researched, and explored the dynamic response mechanism of photosynthetic apparatus to further improve the light utilization efficiency and discover crop yield potential. The major results were summarized as follows:1. The insignificant effect of pulsed light frequencies on Gs value was observed,which didn’t prevent CO2 diffusion from leaf chamber into tomato mesophyll cell.However, the pulsed light frequency distinctly affected Pn character with oscillation. The oscillation range gradually reduced to minimal value(0) accompanied with corresponding increase of light conversion efficiency(LCE′) to maximal value(0.36) when pulsed light frequencies varied from 0.01 Hz to 10.00 Hz. The relative variable quantity of assimilatory charge(ΔACr), which was calculated from oscillation curve of photosynthesis during a period of pulsed light illumination, had almost reduced to 0 values when pulsed light frequencies varied from 0.10 Hz to 10.00 Hz. And relative rate of CO2 uptake(VPn on/off)was equal to 1 or greater than 1. It demonstrated that higher buffering capacity of ribulose-1,5-bisphosphate(Ru BP) pool should play an important role in holding equilibrium state of consumption and regeneration of Ru BP.2. With illumination of tomato leaf by different duty cycles(10%~100%)from pulsed light each at 0.04 Hz, oscillation curve of photosynthesis could demonstrate relaxation time history, therefore it demonstrated photosynthetic oscillation, and the peak values and valleyvalues increased with the increasing of duty cycle. With the increasing of duty cycle, LCE′rapidly increased and reached to a steady station when the duty cycle was 60%. But LCE′of 0.40 Hz is higher than that in 0.04 Hz when the duty cycle was lower than 50%.When Pn demonstrated photosynthetic oscillation each at frequency 0.04 Hz and duty cycle30% ~ 40%, the value of ΔACr was maximum, but the value of VPn on/off closed to 1.Consequently, the stability of photosynthetic oscillation under pulsed light was closely related to the buffering capacity of Ru BP pool. The frequency and duty cycle impacted on Ru BP regeneration and accumulation, therefore they associated the buffering capacity of Ru BP pool.3. The oscillation phenomenon of Pn showed peak-valley type in the pulsed photon flux density of pulsed light with frequency of 0.04 Hz, and there wasn’t oscillation phenomenon in 0.40 Hz. The trend of average carbon assimilation rate(Pn′) for different pulsed light was in the order of continuous light、0.40 Hz and 0.04 Hz. When the pulsed photon flux density was less than 500 μmol·m-2·s-1, the LCE′ of continuous light was more than that under pulsed light. While the pulsed photon flux density was more than 500μmol·m-2·s-1, the LCE′ of 0.40 Hz was more than that under continuous light. Under the pulsed light illumination with frequency of 0.04 Hz and pulsed photon flux density of 600μmol·m-2·s-1, VPn on/off was less than 1 and reached to minimum value, but ΔACr related to Ru BP consumption was in the medium level. When pulsed photon flux density reduced to300~ 400 μmol·m-2·s-1, the ΔACr was lower accompanied with higher value of VPn on/off(more than 1). With the increasing of pulsed photon flux density from 900 to 1500μmol·m-2·s-1, the ΔACr and VPn on/off all gradually increased to 1. Consequently, the relative quantity and rate of Ru BP regeneration and consumption were influenced by frequency and pulsed photon flux density of pulsed light, which was associated with buffering capacity and storage capacity of Ru BP pool.4. Pn charactered with peak-valley oscillation, and oscillation amplitudes of Pn decreased as the increasing of PAR within low intensity time under 0.04 Hz. However, Pn didn’t character with oscillation under 0.40 Hz. The Pn′ under high-low intensity pulsed light rapidly increased as the increasing of PAR within low intensity time, and approached the values under continuous light. The LCE′ each at 0.04 Hz and 0.40 Hz significantly increased than that under continuous light. With the increasing of PAR within low intensity time under 0.04 Hz, ΔACr rapidly decreased and reached to 0, but VPn on/off <1. It demonstrated that Ru BP pool has lower buffering capacity. Consequently, the pulsed light frequency and PAR of pulsed light impacted on LCE′ and the buffering capacity of Ru BP pool, and the optimum combination can significantly improved LCE′ in tomato leaf. |
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