輻射利用效率是以作物碳素同化速率和截取太陽輻射量的比值；此效率是作物生長及產量預測模式化重要的參數。本研究目的在於利用不同量測尺度及方法探討水稻之輻射利用效率，包括利用手持式光合作用分析儀量測單一葉片，通量技術量測水稻田區及統計長期生育資料等方法。結果顯示二氧化碳通量和輻射利用效率與水稻葉面積指數及生質量累積有一致性，而輻射利用效率10年平均值，一期作為0.5至2.0，二期作為0.8至1.8，最高值出現在最高分蘗期，開花期後則開始下降。另比較7種水稻品種在不同高溫及高二氧化碳組合下之輻射利用效率變化，水稻營養期高於榖粒充實期，+2˚C/600ppm組合高於+0˚C/400ppm及+4˚C/800ppm，不同品種在相同環境下輻射利用效率有差異。
The definition of radiation use efficiency (RUE) is carbon assimilated per unit intercepted solar radiation; it is an important parameter for modeling crop growth and yield estimation. Our objectives were to determine radiation use efficiency in rice (Oryza sativa) fields with different measured scales, including measuring single leaves with a portable photosynthesis analyzer, canopy scale with flux techniques and long-term measurement data with a statistic method. Results indicated the CO2 flux and RUE in rice fields were consistent with the change of leaf area index and biomass. The RUE values from the average of ten years (1997-2006) of rice ranged from 0.5 to 2.0 g MJ^(-1) in the first crop, and 0.8 to 1.8 g MJ^(-1) in the second crop. The highest value appeared in the maximum tiller stage and declined during the after-anthesis period. By comparing the leaves of seven rice cultivars under the different combinations of high temperature and CO2 concentration, the radiation use efficiency of the rice vegetative stage was proved to be higher than the grain filling stage. In addition, the combination of + 2˚C/600 ppm was higher than + 0˚C /400 ppm and + 4˚C/800 ppm, and the different responses of RUE among the cultivars under the same environments.
