RESPONSES TO SALINITY OF GRAPEVINE PLANTS WITH SPLIT ROOT SYSTEMS

Grape yield, shoot and root vigour and water use by grapevine plants w ith split root systems were investigated. Some plants had both root pa rts continuously irrigated either with fresh or with saline water. Som e plants got a dual treatment; one portion got fresh water and the oth er saline water. The irrigation water of a third group was changed dur ing the experiment from fresh to saline water or vice versa. Fruit yie ld and root and shoot viability were positively correlated with the ac tual water use. Water ascent along the stem of the grapevines was foun d to be sectorial. Most of the water was supplied by the freshwater ro ots. Only small quantities of water were supplied by salt-affected roo ts to their respective twigs. Changes in the water quality of the root medium induced a dual effect: (a) a fast response, caused by the dire ct change in the ambient water potential; and (b) a long-term response that developed over several weeks. The latter response was induced by the development of new roots, or by death of others, upon a change in the quality of the irrigation water. The commonly used grapevine plan ts of the Arava valley are negatively affected by NaCl already at conc entrations below 100 mm. Under such conditions, shoot growth and fruit yield were seriously inhibited, even when one part only of the root s ystem was exposed to saline water.