INFLUENCE OF WATER-STRESS ON GRAPEVINES GROWING IN THE FIELD - FROM LEAF TO WHOLE-PLANT RESPONSE

A comparative study of soil-plant water relations was conducted on thr ee grapevine cultivars (Vitis vinifera L. cvv. carignane, merlot, shir az) to investigate their adjustment to short-term and long-term water stress under field conditions. Adjustment was a function of the relati ve stability of the internal plant water status on diurnal and seasona l scales. On a diurnal scale, stomatal closure in response to water va pour pressure directly contributed to this stability. Indirect evidenc e suggested an influence of the soil water status on the diurnal stoma tal activity. On a seasonal scale, sufficient leaf hydration required high whole-plant hydraulic conductance. This was achieved by either da ily stomatal regulation or limitation of leaf area. Physiological adju stment to water stress through stomatal control was well developed in cv. carignane, which originated in a Mediterranean environment. Howeve r, cv. shiraz, which was of mesic origin, apparently adjusted to water stress by reducing leaf area. Our study demonstrates the utility of i ntegrating data on stomatal conductance, leaf water potential and whol e-plant hydraulic conductance to interpret whole plant adaptation to w ater stress, and elucidates two mechanisms by which genotypes differen tially acclimate to water stress.