Photosynthetic characteristics of Japonica rice leave under alternative stress of drought and waterlogging

Photosynthesis determines the growth and dry matter accumulation of rice, and drought and waterlogging stress can inhibit the photosynthesis of rice. Study on the light response curve would help to understand the photosynthetic characteristics of rice in a more detailed way. Pot experiments were performed to research the effects of alternative stress of drought and waterlogging (ASDW) at tillering and jointing stage on rice leaf photosynthesis, light response and CO2 response, including net photosynthetic rate, stomatal conductance, potential water use efficiency and intercellular carbon dioxide concentration. Four treatments were set up in 2013 at tillering stage of rice (the water depth of waterlogging was 10 cm) including light drought (T-LD) and severe drought (T-HD), at jointing stage (the water depth of waterlogging was 15 cm) including light drought (S-LD) and severe drought (S-HD). Irrigation with water depth at 0-5 cm except for drying yellow ripening stage (CK) was the control. The experiments were conducted in the greenhouse of Key Laboratory of Efficient Irrigation-Drainage and Agricultural Soil-Water Environment in Southern China (Hohai University), Ministry of Education. The results indicated that rice leaf photosynthesis was inhibited by ASDW at the both tillering and jointing stage, and photosynthetic capacity recovered as the stress changing from drought to waterlogging; At the end of water stress, the net photosynthetic rate of T-HD treatment was lower than that of T-LD and CK (P<0.01); The stomatal conductance of T-LD and T-HD treatment was reduced by 72.93% and 85.01% and the intercellular carbon dioxide concentration was also significantly lower than CK, but the potential water use efficiency was more than two times of CK; The net photosynthetic rate of S-HD treatment was significantly lower than that of CK (P<0.01), while S-LD was lower than CK by 18.66%; The stomatal conductance of S-LD was close to CK, and that of S-HD was 62.73% lower than that of CK (P<0.01); and The intercellular carbon dioxide concentration of S-LD and S-HD treatments showed an increasing trend, and S-LD was 21.57% higher than CK (P<0.05), S-HD reached 1.50 times of CK, but potential water use efficiency of S-HD and S-LD treatments were lower than that of CK, and S-HD was 29.58% lower than CK (P<0.01). After stress, water stress treatments showed obvious compensation effect; On October 10th, the net photosynthetic rate, stomatal conductance, and intercellular carbon dioxide concentration of water stress treatments were significantly higher than those of CK (P<0.05); The potential water use efficiency of S-LD treatment was higher than that of other water stress treatments, but was still lower than CK by 21.35%. The net photosynthetic rate of water stress treatments was lower than CK under the same light intensity, but the light compensation point (LCP), light saturation point (LSP) and dark respiration rate were higher than that of CK, and net photosynthetic rate of rice CO2 response curve was increased. In the tillering stage, the photosynthetic capacity of the light drought treatment was strong, which was weak of the light drought treatment at jointing stage. But in the ripening period, photosynthetic rate of the two severe drought stress treatments were higher than that of light drought treatments. Alternative stress of drought and waterlogging decreased the maximal rate of photosynthesis, but improve the carboxylation efficiency, change the photosynthetic rate turning point of CO2 response curve. After the stress, increasing the light intensity appropriately and prolong the illumination time would be conducive to the rapid growth of rice. But the final yield of each treatment was significantly lower than that of CK (P<0.05). The results can provide valuable information for analyzing the accumulation of dry matter and irrigation water use efficiency of rice, and further proved that drought stress in the early did not reduce the ability of waterlogging tolerance of rice in the late, and slight drought-waterlogging stress in the early stage would be helpful for enhancing rice drought ability from the perspective of photosynthesis. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.