A. Lang et Rk. Volz, SPUR LEAVES INCREASE CALCIUM IN YOUNG APPLES BY PROMOTING XYLEM INFLOW AND OUTFLOW, Journal of the American Society for Horticultural Science, 123(6), 1998, pp. 956-960
The effects of spur leaf removal on xylem sap flows and calcium accumu
lation in fruit of apple (Malus xdomestica Borkh. 'Royal Gala') were d
etermined 56 to 61 days after full bloom. Fruit calcium concentrations
were reduced but fruit size was not influenced by partial spur defoli
ation at bloom. Apples exchanged xylem sap with the tree in daily cycl
es of flow reversal. The presence of local spur leaves promoted this e
xchange by accentuating the xylem sap drawn out of the fruit during th
e day, requiring more to flow back into the fruit at night to replace
it. Calcium concentrations were lower in the xylem sap leaving the fru
it than in that entering it. The reduced calcium accumulation in the f
ruit borne on defoliated spurs can therefore be attributed to the redu
ced volume of xylem sap exchanged between tree and fruit.