Abstract:Influence of soil salinity on crops is a very complicated process. Planting crops on saline-alkali lands have become one of important restricts in sustainable agricultural development. Xinjiang, locating in the arid region of Northwest China, is encountering serious soil salinization. Wheat is the most commonly grown cereal crop in Xinjiang. Wheat cultivation in saline-alkali lands based on drip irrigation has become the key of agricultural development in Xinjiang. However, the changes of photosynthetic characteristics of wheat under drip irrigation with soil salt content are still not clear, and the salt-tolerance indexes such as salt-tolerance critical value and salt-tolerance limit are unknown in this region. Therefore, it is necessary to explore effects of soil salt content on photosynthetic characteristics and yield component of spring wheat under drip irrigation, comprehend the photosynthesis restriction mechanism of spring wheat as well as the correlation between its yield and soil salt content, and determine salt-tolerance indexes. The pot experiment was carried out in the test site of Key Laboratory of Modern Water-saving Irrigation Corp of Shihezi University from March to October, 2015. Five treatments were set, including growing wheat in non-saline soil, mild saline soil, moderate saline soil, strong saline soil and saline soil, respectively, and each treatment had three replicates. Soil salt contents of the five treatments were 2.0g/kg (CK), 5.0g/kg (T1), 9.0g/kg (T2), 16.5g/kg (T3) and 24.5g/kg (T4). Each plot adopted the same irrigation and fertilization management independently. Dripper flow for drip irrigation was controlled at about 1.8L/h. The irrigation amount for each time was 44mm and totally 11 irrigations were given during the growth period. Photosynthetic characteristics of spring wheat at elongation stage (May 20th), heading stage (May 28th) and milk-ripe stage (June 11th) were tested by using the CI—340 portable photosynthesis system (USA). Test items included environmental indexes (photosynthetically active radiation, air temperature and CO2 concentration in air) and photosynthetic physiological indexes (net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration). Stomatal limitation and non-stomatal limitation values of leaf photosynthesis were calculated according to the recorded data. Meanwhile, changes of spring wheat yield and soil salt content were observed. Salt-tolerance indexes were calculated through linear regression analysis. Results showed that soil salt content significantly affected photosynthetic physiological indexes of spring wheat under drip irrigation. Coexistence of stomatal and non-stomatal factors inhibited leaf photosynthesis of spring wheat. Reduction of net photosynthetic rate under low soil salt content was mainly caused by stomatal factors, while its reduction under high soil salt content was mainly caused by non-stomatal factors. Salt-tolerance critical value and salt-tolerance limit of spring wheat (0~40cm) in Xinjiang under drip irrigation were 6.46g/kg and 30.72g/kg, respectively. When soil salt content was controlled lower than 9.63g/kg, the relative yield of spring wheat under drip irrigation could be generally higher than 90%. It was concluded that spring wheat was suitable to be grown with drip irrigation in non-saline and mild saline soils. The results could provide theoretical supports for field management and high-efficient production of spring wheat using drip irrigation in saline-alkali soils in Xinjiang.
