Photosynthetic Performance in the Leaves of Different Mung Bean Genotypes

Photosynthesis is closely related to crop growth and yield, and higher photosynthetic rate of leaves is one of the important factors for high crop yield. The study explored the changes of photosynthetic indexes of the leaves at different flowering nodes in high-yield mung bean varieties Jilu 2 and An 9910, and low-yield varieties Chifeng and Tailai adopted in the summer planting region,thus to clarify the physiological characteristics affecting seeds yield and photosynthetic performance of the leaf in mung bean at the late growth stage. The results showed that after flowering, the leaves gradually aged, the net photosynthetic rate (Pn), transpiration rate (Tr), stomata conductance (Gs), chlorophyll and soluable protein contents of its functional leaves gradually declined, but the intercellular carbon dioxide concentration (Ci) of the leaves tended to rise, specific leaf weight tended to decline-rise-decline. The photosynthetic capacities of the leaves appeared to decline from the upper nodes to the lower nodes. Compared with low-yield varieties, the leaves of Jilu 2 and An 9910 had a longer functional period, declining slowly in chlorophyll and soluable protein contents and maintaining higher photosynthetic capacity at the late growth stage, which provided a good physiological foundation for higher amount of accumulated photosynthates . Further analysis indicated, there were significant positive correlations between seed yield and average net photosynthetic rates of leaves at flowering nodes(r=0.999), and between net photosynthetic rate and the contents of chlorophyll and soluble protein at the late growth stage. In summary, at the crucial stage of yield formation, maintaining higher chlorophyll content and photosynthetic capacity of functional leaves, and delaying leaf aging have important action for increasing crop yield.