Response of single leaf photosynthesis and transpiration to red light and UV-A radiation in two different plant-type rice cultivars (Oryza sativa L.)

The influence of red light and ultraviolet (UV)-A radiation on the single leaf photosynthesis and transpiration were investigated in two different plant-type rice cultivars: active tillering type, Hopumbyeo (HP) and low-tillering heavy panicle type, Shindongjinbyeo (SDJ) at maximum tiller number stage. An open photosynthesis measurement system was used to monitor CO₂ exchange rate, which was determined by decrement of CO₂ concentration at the out let of leaf chamber comparing with the concentration of incoming ambient air. The results suggested that CO₂ exchange rate increased linearly with increasing of red light up to 254 μmol m^-2s^-1 in the two cultivars. This linear response rate was consistent even if UV-A was included or not. An effect of UV-A radiation was found only in transpiration; transpirations of both cultivars increased with increasing of UV-A level, and there was significantly difference of transpiration rate between two cultivars. The CO₂ exchange rate in single leaf was higher in SDJ than that in HP, whereas transpiration rate was higher in HP than that in SDJ. Considering higher CO₂ exchange rate together with lower transpiration in SDJ indicated that some other cultivars rice genetic resources could use to enhance rice yield potential and water use efficiency in an irrigated rice system.