Influence of Water Deficit Stress on Leaf Area Development and Transpiration of Sangiovese Grapevines Grown in Pots

A stable, conservative variable is needed to describe the level of water-deficit stress to which grape- vines are subjected. In agronomic crops, a function based on the amount of transpirable water stored in the soil has been found to provide such stable functions. This initial study examined whether this approach could be used to describe the response of transpiration rate and leaf area development rate in grapevines. The soil in which four- year-old grafpevines (Vitis vinifera L. cv. Sangiovese) were growing was allowed to dry over several days. Both tran- spiration rate, which is assumed to be proportional to the gas exchange capability of the plant, and leaf area de- velopment rate did not decrease until the fraction of the transpirable soil water (FTSW) declined to about 0.35. Below 0.35 FTSW there was a continuous decline in each process utnil they were zero at FTSW=0. The overall behavior of the plants to the drying soil was well described by logistic equations based on FTSW.