RESPIRATION OF APPLE-TREES BETWEEN LEAF FALL AND LEAF EMERGENCE

Respiratory CO2 loss of apple (Malus domestica Borkh.) was measured in situ, using tree chambers and computerized infrared gas analysis with a dedicated interface and software, over two years, from November 198 8 to March 1990 in which the first autumn/winter period was relatively cold and the second period was relatively warm. In the first, the col der winter of the study, respiration of a three-year-old apple tree de clined from 60-120 mg CO2 tree(-1) hr(-1) after leaf fall in November to minimum values of 30-50 mg CO2 hr(-1) (0.2-0.3 mu mol CO2 s(-1)) in December/January. In the second, the warmer winter of the study, the then four-year-old apple tree with still attached leaves assimilated 1 500 mg CO, hr(-1) during daytime in November, with dark respiration of 500 mg CO2 hr(-1), attributed to translocation of carbohydrates into the woody perennial parts of the tree later in the year in the warmer autumn. With daytime CO2 assimilation exceeding dark respiration, the leaves of the apple tree still gained carbon in the warmer November, w hile the tree lost carbon in the colder November. Associated with the date of leaf fall, the switch from net photosynthesis to net respirati on during the day occurred earlier in the colder winter (November) tha n in the warmer winter (mid-December), a time when the tree lost exces sive carbon. Minimum respiration values exceeded 50 mg CO2 hr(-1) tree (-1) in the warmer December/January compared to 30 mg CO2 hr(-1) tree( -1) in the colder December/January. Minimum carbon losses were encount ered in December (colder winter) or January (warmer winter), with date and minimum Values depending on ambient temperature. After leaf fall, the temperature response of the trunk plus branches gave an averaged Q(10) of 2.55 (5 degrees C/15 degrees C). These data represent the fir st comprehensive carbon balances of apple trees in situ between leaf f all and leaf emergence.