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

摘要

In Chile, table grape (Vitis vinifera L) varieties are commonly grown on a particular trellis structure, named "parronal". Due to the horizontal distribution of the leaf layers, this system leads to big attenuation of the photon flux density (PFD) throughout the canopy, particularly when plants reach a leaf area index around 4. This commonly occurs after veraison when demand for photosynthates starts to be an active process. At that time, almost all of the direct PFD is intercepted by leaves growing on top of the canopy, raising concern about the real contribution of lower leaf layers to the total CO_2 assimilation of the plants. In fact, leaves situated on the lower layers would be close to the PFD compensation point for most of theday. This hasmade to suppose that in grapevine most of the photosynthates transported to the clusters come from leaves directly exposed to the sun (Smart 1974). However, in parronal system this seems to be not totally clear. Depending on the sun position and intensity of wind, leaves from the lower layers can also be reached by direct PFD in the form of sunflecks. As a consequence, parts of the lower canopy can have high photosynthesis rates for different periods. Contribution of this to the total plant photosynthesis is not well known and has not been evaluated in the parronal system.