THE INFLUENCE OF PHOSPHORUS AVAILABILITY AND ROOTSTOCK ON ROOT-SYSTEMCHARACTERISTICS, PHOSPHORUS UPTAKE, PHOSPHORUS PARTITIONING, AND GROWTH EFFICIENCY

Chenin blanc grapevines on either Freedom or St. George rootstock were grown under sufficient (+P) and deficient (-P) soil phosphorus availa bility. Root system morphology was similar for both rootstocks regardl ess of P availability. Vines on Freedom accumulated more P than did vi nes on St. George, especially under -P. There was a marked decrease in the amount of P translocated to the shoot and accumulated in the peti oles of vines on St. George with decreasing P availability. Also, vine s on Freedom produced more shoot growth per unit P than did vines on S t. George, particularly under -P, although P use efficiency for overal l vine growth was not influenced greatly by rootstock. Differences in P uptake, translocation, and growth efficiency may account for differe nces in shoot growth inhibition between vines on St. George and Freedo m observed in our earlier study. Vines on the different rootstocks par titioned different amounts of P into petioles under +P, but not under P-deficient conditions.