Effects of different growth stage irrigations on small-grainpeanut leaf photosynthetic characteristics

This study analyzed the effects of irrigation at different growth stages on peanut leaf photosynthetic and physiological characteristics and determined the period of maximum water efficiency in peanuts. The rainproof installation pool culture method was used in the study. Two small-grain peanut varieties ("HY 20" and "HY 27") were subjected to five treatments of irrigation - irrigation during the entire growth stage (CK), drought stress during the entire growth stage (T1), irrigation at seedling stage (T2), irrigation at flower-pegging stage (T3) and irrigation at pod-setting stage (T4). Photosynthetic pigment contents and chlorophyll fluorescence parameters of different peanut varieties were comparatively analyzed. The results showed that change in leaf chlorophyll-a content of the two peanut varieties was not significant under different growth-stage irrigations. However, different treatments yielded different ranges of increase or decrease in chlorophyll-a content. Leaf carotenoid content under different soil water conditions was different for the two varieties. Also peak times for carotenoid content under drought-stress treatment were different for the two varieties. Irrigation at pod-setting stage increased chlorophyll-b and carotenoid contents. "HY 27" Fv/Fm value in the entire growth stage irrigation was higher than that of "HY 20", which meant that light energy conversion efficiency of "HY 27" was stronger than that of "HY 20". Irrigation at pod-setting stage of both varieties improved Fv/Fm and Fv/Fo values and increased light energy conversion efficiency. This was an effective way of avoiding or alleviating damage to photosynthetic apparatus. Irrigation at flower-pegging stage, pod-setting stage and in entire growth stage yielded higher apparent photosynthetic electron transport rate (ETR) and non-photochemical quenching coefficient (Q_N) values with higher retained total photosynthetic reaction. Irrigation at seedling stage of the two varieties did not increase net photosynthetic rate (Pn) at the late growth stage. In the entire growth stage under different irrigation treatments, Pn, Gs and Ci declined. This meant that stomatal limitation was the main factor for decline in peanut Pn under water-stress condition. Overall, irrigation at flower-pegging stage and pod-setting stage improved leaf photosynthetic capacity, indicating that irrigation after peanut flowering was cost-effective.