INTERACTIONS OF LEAF AGE, FRUITING, AND EXOGENOUS CYTOKININS IN SANGIOVESE GRAPEVINES UNDER NONIRRIGATED CONDITIONS .1. GAS-EXCHANGE

The interactions of leaf age and gas exchange, together with modifications induced by fruiting and exogenous kinetin treatments, were investigated in field-grown Sangiovese (Vitis vinifera L.) grapevines. Analyses carried out both on a seasonal basis and within each sampling date as a function of the natural gradient of age along the shoot showed that maximum Pn occurred at 30 to 35 days of age. A progressive decline started at about 50 days and four-month-old leaves retained 45% of maximum Pn. Very young, rapidly expanding leaves (< 15 days) also showed a consistently lower Pn and water use efficiency (WUE) than recently fully expanded leaves. Differential rates of leaf senescence due to fruiting or kinetin were not observed. These data form a basis for improving the physiological understanding of widely used vineyard management operations (shoot topping, leaf removal) which normally induce variations in canopy leaf age.