Abstract: 【Objective】 Relationship between diurnal changes of net photosynthetic rate and environmental factors in leaves of Z. latifolia were studied. The results provided scientific basis for using resources of Z.latifolia.【Method】Diurnal changes of net photosynthetic rate and environmental factors in leaves of Z.latifolia were measured using Li-6400 portable photosynthesis system. The relationship between net photosynthetic rate and environmental factors were analyzed by correlation analysis.【Result】The net photosynthetic rate was in the range of 15.0-21.5 ?mol·m-2·s-1 in un-folding leaves of Z.latifolia. Light compensation point of photosynthesis of Z.latifolia in un-folding leaves was 45 ?mol·m-2·s-1. Light saturation point of photosynthesis was 1 040 ?mol·m-2·s-1. Diurnal changes of the net photosynthetic rate, stomatal conductance and transpiration rate were all one-peak curve in leaves of Z.latifolia. The peak of net photosynthetic rate was measured at 11:00 a.m., the average net photosynthetic rate in leaves of Z.latifolia at 8:00-11:00 was higher 4.7 ?mol·m-2·s-1 than at 13:00-16:00. The peaks of stomatal conductance and transpiration rate were measured at 13:00 and 14:00 p.m. During a day, the net photosynthetic rate was significantly positively correlated with photo flux density (PFD) at 5:00-11:00 a.m. and 15:00-19:00 p.m. Correlation coefficient were 0.9874** and 0.9321**, respectively. The net photosynthetic rate showed little positive correlation with PFD at 11:00-15:00. The correlation coefficient was 0.4440. The net photosynthetic rate showed significantly positively correlated with temperature at 5:00-11:00 a.m. and 15:00-19:00 p.m. The correlation coefficients were 0.9617** and 0.9852**, respectively. The net photosynthetic rate was significantly negatively correlated with temperature at 11:00-15:00. The correlation coefficient was -0.8110*. The net photosynthetic rate was significantly positively correlated with stomatal conductance, and was significantly negatively correlated with intercellular CO2 concentration. The correlation coefficients were 0.7936* and -0.8026*, respectively. Stomatal conductance and transpiration rate were significantly positively correlated with PFD. The correlation coefficients were 0.9104** and 0.7858*, respectively. 【Conclusion】Light compensation point of photosynthesis of Z.latifolia in un-folding leaves is lower, but light saturation point of photosynthesis is higher. Z.latifolia is adaptable widely to photo flux density and is a typical heliophyte. Photo flux density and air temperature are major environmental factors influencing diurnal changes of net photosynthetic rate.

Key words: Zizania latifolia, Photosynthetic rate, Diurnal changes, Stomatal conductance, Environmental factors