Seasonal changes in total nonstructural carbohydrates within branches and roots of naturally 'off' and 'on' 'Kerman' pistachio trees

Abstract

The objective of this investigation was to determine the dynamics of carbohydrate use as revealed by soluble sugar and starch and concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary scaffold branches and roots (≤10 mm in diameter) of alternate-bearing 'Kerman' pistachio (Pistachia vera L.) trees that were in their natural bearing cycles. Two hypotheses were tested. First, carbohydrate concentration is greater early in the growing season in organs examined from heavily cropping ('on') than light cropping ('off') trees. This hypothesis was affirmed as judged by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary branches and roots of 'on' compared to 'off' trees. Second, carbohydrate concentration remains high in 'on' tree organs as the first wave of inflorescence bud and nut abscission occurs early in the growing season. This hypothesis was also affirmed. In fact, soluble sugars and starch remained high in 'on' trees through full bloom FB + 60 days (FB + 60) as inflorescence bud and nut abscission occurred. In the persisting 'on' tree inflorescence buds, sharp decreases in soluble sugars and starch were evident by the final sample date when 'off' tree inflorescence buds contained a 13 times greater concentration of soluble sugars and starch than 'on' tree buds. At that time, 'off' tree inflorescence buds contained 50% more dry mass than 'on' tree inflorescence buds. After FB + 60, 'on' tree soluble sugars and starch declined in all organs as nut growth occurred. During the same time period, organs of 'off' trees began to accumulate greater concentrations of soluble sugars and starch and exceeded concentrations measured in organs of 'on' trees.