SUMMARY RESEARCH REPORT Research Project for Higher Utilization of Forestry and Agricultural Plant Materials in Thailand (HUFA) - Physiological Characteristics of Paper Mulberry in Experimental Plot

Abstract

Paper mulberry, Si Satchanalai (Broussonetia papyrifera) and Kozo (Br2oussonetia kazinoki) cultivars were grown in the experimental field of Kamphaeng Saen campus. The light response and CO2 compensation were measured for mature leaves of 24 days old. The photochemical efficiency, , is in the range of 0.060-0.063 mol mol-1 , and the P values are 25.6-31.6 mol m-2 s -1 , with light saturation of about 880 mol m-2 s -1 . The CO compensation is 61 mol mol-1 , and the carboxylation conductance is in the range of 107-111 mmol m-2 s -1 . The parameters indicate no distinct difference in the photosynthesis apparatus between the two cultivars. The similar light reaction rate is further confirmed by the measurement of chlorophyll fluorescence. The average quantum yield of dark-adapted leaf (Fv/Fm) is 0.822 for SS and 0.808 for KZ. The reaction centers of paper mulberry employed a photoprotection mechanism when the PPF intensified during the course of the day. One measurement of diurnal change in gas exchange and water potential was made on leaves of 30 days old of 8 month-old plants in September, 2000. The matric potential of active root zone of 30 cm, was low at 53 kPa at the start of the day. So the root was in mild water stress. The sky was overcast, with only 2 hours of strong radiation during 10-12 hr. Kozo showed consistently higher rates of net photosynthesis (A), transpiration (E) and greater stomatal conductance (gs). The peak A was only half of Pm, which was the result of both low PPF and lower gs under stress. The gs of KZ was more responsive to change in total potential ( t) of the leaf and was higher than SSs at the same level of t. The solute concentration of leaf sap changed following the rate of A, which was higher for KZ. Averaged over the day, KZ leaves were at lower total potential, but the higher solute concentrations enabled the leaves to gain slightly higher turgor than the SSs. The biomass determination of each plant at 5 months old showed that KZ plant had more dry mass. We propose from this study that the faster growing rate of KZ does not come from the higher performance of the potential photosynthesis, but from the more dynamic opening of stomata, thus the higher rates of gas exchange under the field conditi