The characteristics of photosynthetic rate in response to light intensity and the rules of diurnal variations in photosynthesis, light use efficiency and water use efficiency of the representative soybean leaves during the filling period in the Northeastern China were determined and investigated under the artificial and field conditions by using the portable photosynthesis system(LI-6400).The results showed that photosynthetic rate in response to the photosynthetically active radiation flow followed a typic...