Light utilisation and thermal dissipation in light- and shade-adapted leaves of Vitis genotypes

Light responses of chlorophyll fluorescence and photosynthetic parameters were determined using light- and shade-adapted leaves of cvs Muller-Thurgau, Riesling and Dornfelder. The quantum yield of photochemical energy conversion (Y) decreased with increasing light intensity (PAR), shade-adapted leaves showing a stronger decline already at very moderate PAR. For both leaf types the electron transport rate (ETR) increased with PAR but to distinctly higher values in light-adapted leaves. Correspondingly, rates of maximum CO2 assimilation at ambient CO2 concentration (A max) and stomatal conductance a A max were higher in light-adapted than in shade-adapted leaves, cv. Dornfelder always showing higher photosynthetic performance than cvs Riesling and Muller-Thurgau. Maximum ETR of light-adapted leaves of 11 genotypes varied between 85 (Müller-Thurgau) and 220 (Lemberger), red genotypes generally showing higher values than white genotypes. In light-adapted leaves of cvs Muller-Thurgau, Riesling and Dornfelder non-photochemical quenching (NPQ) increased up to PAR = 2,350 µmol m-2 s-1. In shade-adapted leaves of Muller-Thurgau and Riesling NPQ reached saturation already at PAR = 500 µmol m-2 s-1, indicating a limited capacity for thermal dissipation of energy; in contrast, in shade-adapted leaves of Dornfelder the NPQ increase was similar to that of light-adapted leaves. The beta -carotene and lutein content and the xanthophyll pool size (violaxanthin + antheraxanthin + zeaxanthin) of light-adapted leaves (cvs Muller-Thurgau, Riesling and Dornfelder) were higher than in shade-adapted leaves. In light-adapted leaves the xanthophyll pool was lowest for Muller-Thurgau and highest for Dornfelder indicating a higher capacity of thermal dissipation of energy for the latter variety. It is concluded that the high photosynthetic fight use and photoprotective ability of Dornfelder contribute to its lower proportion of excess PAR and reflect its superior ability for adaptation to high light.