The relation between water use efficiency and photosynthesis characteristic under different N level.

The photosynthesis parameter and environment factors of maize leaves were determined by LI-6400 portal photosyntometer at jointing,silk and filling stage under different N level to study the relation between water use efficiency and photosynthesis rate,transpiration rate,stomatal conductance,stomatal conductance,intercellular CO2intensity.The results showed that the water use efficiency under high N level was higher than that under low N level at different growth stage,the water use efficiency increased with increase of photosynthesis rate and stomatal conductance and decreased when photosynthesis rate and stomatal conductance were above 23 μmolCO2/(m2·s) 22 μmolCO2/(m2·s) and 0.20 mol/(m2·s),0.18 mol/(m2·s) respectively under two N levels,and the water use efficiency increased with increase of transpiration rate when transpiration rate was below 3.00 mmol H2O/(m2·s) and decreased when transpiration rate was above 3.00 mmol H2O/(m2·s)under two N levels.