Photosynthetic contribution rate and response of Phalaris arundinacca leaves at the different position in filling stage to light intensity

In the present study, Phalaris arundinacca leaves at different position in filling stage were irradiated with ten different built-in light intensity including 0, 50, 100, 200, 500, 800, 1 100, 1 400, 1 700, 2 000μmol·(m2·s)-1. The photosynthetic parameters such as photosynthetic rate, transpiration rate, stomatal conductance, photosynthetic contribution rate and water consumption rates of leaves from first to fourth position were measured to investigate the response of the P. arundinacca leaves at different position to light intensity and its photosynthetic contribution rate. The results showed that P. arundinacca can use more than 50 mol·(m2·s)-1 intensity light for photosynthesis. Leaf photosynthetic parameters were extremly significantly affected by light intensity and leaf position (P<0.01). The net photosynthetic rate, stomatal conductance, intercellular CO2 concentration (Ci) and transpiration rate (Tr) of P. arundinacca leaves at different position had no significant difference with 500~1 700 μmol·(m2·s)-1 illumination, however, there was photoinhibition when the light intensity was greater than 1 400 μmol·(m2·s)-1. Water use efficiency reached the highest with 800~1 400 μmol·(m2·s)-1 illumination. With natural light, the photosynthetic rate and intercellular CO2 concentration per unit leaf area of P. arundinacca leaves at different position had significant difference (P<0.05). The photosynthetic rate, contribution rate and water use efficiency of second and third leaf were higher than those of other leaves. Therefore, the more attention should be paid to maintaining the integrity and health of first to third leaf for field management in order to obtain adequate nutrition for seed development of P. arundinacca.