Influence of Fruit Load on Water Consumption, Leaf Photosynthesis and Plant Nutrient Contents of Longan Trees Grown in Sand Culture

The effects of fruit load levels on water consumption, photosynthesis characteristics and leaf nutrient concentrations of 3-years-old grafted longan trees cv. 'Daw' were investigated from February to September 2008. The longan trees were grown in lysimeter tanks of 100 liters capacity, which were filled with sand and irrigated with Hoagland nutrient solution. The CRD experimental design consisted of 4 levels of fruit load, i.e., 1) heavy, 2) medium, 3) low and 4) no load. The result showed that water consumption levels of all treatments were similar. However, all fruit load treatments had higher levels of leaf dark-adapted chlorophyll fluorescence, net CO2 exchange, transpiration and stomata conductance than the no fruit load treatment. High fruit load tree had the highest fruit number per panicle, fruit weight per panicle, total yield and total leaf non-structural carbohydrate (TNC) content. However, the high fruit load significantly resulted in lower fruit weight, fruit size and aril thickness. Leaf K, Ca and Mg concentrations were lowest in the high fruit load treatment, but all treatments had no effect on the leaf N and P contents.