Photosynthetical characterization of different leaf layers of field - grown grapevines cv Thompson Seedless.

Abstract

Table grape producing systems in Chile are mostly parronal type (horizontal canopy at 2 m height). This leads to canopies with leaf area indices higher than 4 where there is big variation in the light intensity over the leaves. The objective of this work was to determine the photosynthetical characteristics of two types of leaves: those growing on top of the canopy and those growing on the lower part of the canopy. Three times during the 2000-2001 season, field-grown leaves that grow under two different PFD levels were evaluated in terms of photosynthetic parameters: fluorescence and CO2 exchange. It was found that leaves growing on top of the canopy are submitted to stress par excess PFD (values higher than 1500 micromol·m-2·s-1) and high temperatures, showing Fv/Fm values ranging between 0.75 and 0.3. Leaves on the lower part of the canopy (PFD ranging between 10-100 micromol·m-2·s-1) are very stable with values of Fv/Fm over 0.8. In terms of CO2 exchange both type of leaves increase photosynthesis up to 600 micromol·m-2·s-1, but the net CO2 rates are very different, being almost 10 times higher for top leaves.