Photosynthetic light responses in relation to leaf temperature in sun and shade leaves of grapevines

Dennis Greer, Mark Weedon

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7 Citations (Scopus)
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How light attenuation influences the photosynthetic properties of different leaves within grapevine canopies was investigated by measuring photosynthesis along the shoots over the growing season and light responses of selected leaves derived at different temperatures. Differences in rates of photosynthesis became apparent in late spring when the canopies start to close; rates of photosynthesis of shaded leaves peaked at 7 'mol (CO2) m-2 s-1 some 40% behind exposed leaf rates, and these differences accentuated as the season progressed. By mid-season, rates of photosynthesis at 12 'mol (CO2) m-2 s-1 were nearly three-fold higher in sun compared with shade leaves at 5.5 'mol (CO2) m-2 s-1. Basal and mid-node position leaves gradually become shaded while leaves at the apical shoot end still maintained high rates. Photosynthetic light responses showed typical sun/shade contrasts with higher maximum photosynthesis, lower apparent photon yields and higher light-saturation in the sun leaves. However, these responses were highly temperature ' dependent and Pmax was optimal at 25oC and declined at 20 and 35oC and above. Similarly, the apparent photon yield was also highly temperature-dependent, optimal at 25oC and declining with increasing temperatures. By contrast, light intensities required to saturate photosynthesis increased from about 600 'mol (photons) m-2 s-1 at 20oC to over 1100 'mol (photons) m-2 s-1 at 35 - 40oC. We conclude that although shade has a marked impact on photosynthesis, the temperatures that the vines experience over the growing season also has a marked impact on the photosynthetic responses to light.
Original languageEnglish
Pages (from-to)149-156
Number of pages8
JournalActa Horticulturae
Publication statusPublished - Oct 2012

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