Post-harvest photosynthesis of apple leaves

摘要

Photosynthesis and transpiration of apple (cv. Golden Delicious) leaves were determined after fruit harvest (end of September) up to leaf fall (end of November). Environmental conditions were the primary limiting factor for photosynthesis during this period. In November (photosynthetically active radiation (PAR) of <1400μmol, 10deg C) photosynthesis still reached 4.2μmol CO2 m-2 s-1. Photosynthesis and transpiration potential, measured under controlled laboratory conditions (700μmol m-2 s-1 and 21deg C) remained relatively large (9.5μmol CO2 m-2 s-1 and 1.8 mmol H2O m-2 s-1) until a first frost, indicating residual stomatal activity. Leaf chlorophyll content remained high until November (42-44μg/cm leaf area; saturating for leaf photosynthesis). Thereafter, a breakdown, primarily of chlorophyll a, reduced the chlorophyll a:b ratio. With 8% of dry matter, sorbitol showed the highest concentration of all leaf carbohydrates (starch 2%) reflecting translocation of carbohydrates to the perennial woodyorgans of the tree. Leaf N and K contents decreased slowly after harvest, whereas Ca and Mg contents appeared hardly affected.