Abstract
To investigate the influence of water deficit on the diurnal changes of net photosynthetic rate, transpiration rate, stomatal conductance and its any correlation, two Korean cultivars and one Japanese cultivar were grown in Wagner pots in phytotron. Treatment of soil moisture deficit was carried out by stopping irrigation 30 days after germination. Under soil-water deficit conduction, net photosynthetic rate, transpiration rate and stomatal conductance of the soybean plants were higher in the morning, but they decreased very quickly in broad day. Similar patterns of the diurnal changes were found with lower values day by day in the proceeding soil-water deficit. Plant water status recoverd net photosynthetic rates, transpiration rates of next morning to some extent, but it was effective under relatively mild water deficit condition. The water use efficiency (WUE) increased with decreasing soil moisture to 34% soil moisture, showing maximum value of WUE and decreased at levels over this content.
