Photosynthetic Characteristics and Development of Longan Leaf

Changes in longan (Dimoparpus longan Linn.) leaf photosynthetic characteristics with leaf age, growth and development were determined. The experiment was conducted at the Agricultural Technology Research Institute, Rajamangala University of Technology Lanna, Lampang. Ten longan trees were pruned on June 1, 2010. The result showed that longan trees began flushing about 22 days after pruning, leaf width and leaf length parameters increased during leaf development and leaf photosynthesis also increased. Leaf expansion parameter correlated with SPAD unit, chlorophyll fluorescence, the net CO2 exchange rate (NCER), transpiration rate and stomata conductance. The longan leaves fully expanded 21 days after terminal bud break (DATBB). Chlorophyll content (SPAD unit) and chlorophyll fluorescence (Fv/Fm) increased from 19.06 to 45.46 between 7 and 28 DATBB and 0.58 to 0.78 between 7 and 21 DATBB, for chlorophyll content and chlorophyll fluorescence, respectively. Moreover, the net CO2 exchange ratel transpiration rate and stomata conductance increased from-1.44 to 9.53 iumol m- s 1, 0.62 to 2.46 mmol m-2 s-1 and 0.02 to 0.34 mol m(-2) s(-1) between 7 and 35 DATBB, for net CO2 exchange, transpiration and stomata conductance, respectively.