DEVELOPMENTAL LIGHT LEVEL AFFECTS GROWTH, MORPHOLOGY, AND LEAF PHYSIOLOGY OF YOUNG CARAMBOLA TREES

Growth and leaf physiology responses of container-grown 'Arkin' carambola (Averrhoa carambola L.) trees to long-term exposure of almost-equal-to 25%, almost-equal-to 50%, or 100% sunlight were studied in four experiments in Guam and Florida. Shading increased rachis length and leaflet area, and decreased leaflet thickness. Shaded trees also had a more horizontal branch orientation. Shading reduced dark respiration (R(d)) and light compensation and saturation points but increased chlorophyll concentration and N-use efficiency. Light-saturated net CO2 assimilation (A) was not affected by developmental fight level. Trees in full sun had smaller total leaf area, canopy diameter, and shoot : root ratio and exhibited leaflet movement to avoid direct solar radiation. Also, trees grown in 100% sunlight had a more vertical branch orientation and greater stomatal density than shaded trees. The ratio of variable to maximum fluorescence (F(v)/F(m)) declined during midday in 100% sunlight trees. This pattern was accompanied by a midday suppression of A in 100% sunlight-grown trees in Guam. 'Arkin' carambola trees exposed to almost-equal-to 25%, almost-equal-to 50%,or 100% sunlight for up to 39 weeks exhibited physiological and morphological adaptations that resulted in similar growth. These results indicate that carambola efficiently adapts to different developmental light intensities.