S20 - Session O4 - Contributions of photosynthetic parameters to overall gas exchange performance varied between vinifera and hybrid grape cultivars

Authors: Mu-Chen Liu, Kuo-Tan Li *

The hybrid grape cultivars ( Vitis vinifera L. x V . labrusca L.) are commonly cultivated in humid subtropical climates due to their superior vigor over the vinifera grapes ( V. vinifera ). However, the leaf structure of hybrid cultivars, inherited from V . labrusca L., often possesses dense trichomes on the abaxial side and would limit the diffusion rates of gas and water vapor, consequently, reducing leaf photosynthetic assimilation rate ( A ). In this study, leaf gas exchanges of vinifera grape 'Riesling' and two hybrid cultivars, 'Black Queen' and 'Golden Muscat', were measured to obtain light response and CO 2 response ( A - C i ) curves at an optimal air temperature of 25℃. The results showed that at ambient CO 2 concentration ( C a , 400 μmol∙mol -1 ), 'Riesling' had the highest A and g s in all three cultivars, while 'Golden Muscat' had the highest intrinsic water use efficiency (WUE). Gas exchange data were fitted in a modified Farquhar, von Caemmerer and Berry biochemical model ( FvCB ) for estimation of dark respiration rate ( R d ), mesophyll conductance ( g m ), Rubisco carboxylation ( V cmax ) and maximum electron transport capacity ( J max ). The results showed that 'Riesling' had the highest J max and V cmax at saturate light. Although g m was similar among the three cultivars, the scatter diagram indicated a positive relation between g m and A at C a , while WUE was more positively related to the ratio of g m to g s ( g m / g s ). A numerical integration approach was applied to partitioning the contributions of A parameters in hybrid cultivars using 'Riesling' as a reference. The outputs indicated that at optimal temperature, A of 'Black Queen' and 'Golden Muscat' was 40% and 38%, respectively, less efficient than that of 'Riesling'. Biochemical factors, mainly J max , contributed 3/4 of the inferior A performance in 'Black Queen', while biochemical and diffusional factors had equals shares in 'Golden Muscat'.