Poster: Photosynthesis

Abs # 311: CO₂assimilation rates and photosystem II activities in Campbell Early and Kyoho grapevine cultivars under various PPFD conditions

Presenter:	Lee, Hee Jae , heejlee@snu.ac.kr
Authors	Lee, Hee Jae  (A)   Yu, Duk Jun  (A)   Kim, Su Jin  (A)
Affiliations:	(A): School of Plant Science, Seoul National University

CO₂ assimilation rates and PSII activities under various PPFD conditions were compared in one-year-old cuttings of Vitis vinifera x V. labrusca cv. Campbell Early and Kyoho grown in pots containing soil, peat, and sand at a rate of 1:2:1. The CO₂ assimilation rate was higher in Campbell Early than in Kyoho by 1-3 mmol m^-2 s^-1 depending on PPFD ranged from 500 to 2,000 mmol m^-2 s^-1. However, apparent quantum yield, light compensation point, and dark respiration rate were similar in both cultivars. Stomatal conductance was cuvilinearly related to CO₂ assimilation rate under PPFD conditions beyond light compensation point, indicating that CO₂ assimilation was affected by both stomatal and non-stomatal factors. Quantum yields of PSII in both cultivars were abruptly increased at 100 mmol m^-2 s^-1 PPFD and then linearly decreased with increasing PPFD. The decrease of quantum yield was associated with the increase of radiationless energy dissipation which was estimated from non-photochemical quenching (NPQ) of PSII. NPQ increased with increasing PPFD. Both cultivars exhibited similar NPQ below 200 mmol m^-2 s^-1 PPFD, but Kyoho showed higher NPQ than Campbell Early at higher PPFD and the difference in NPQ between the cultivars became more apparent with increasing PPFD. Electron transport rate was higher in Campbell Early than in Kyoho beyond 500 mmol m^-2 s^-1 PPFD. The responses of electron transport rate to incident PPFD were curvilinearly related to those of net CO₂ assimilation rate. Our results demonstrated that both cultivars had similar photosynthetic characteristics at low PPFD. At high PPFD, however, Campbell Early exhibited higher CO₂ assimilation rate, while Kyoho had higher excessive energy dissipation of NPQ.