Effect of floating dust weather on leaf photosynthesis and water potential of grapes in Karakash River Basin

Grape provides an important source of income for farmers in Karakash River Basin in Xinjiang. However, floating dust weather conditions are frequent in spring and summer. Thus grape production in the region is greatly influenced by both the floating dust weather and spring water scarcity. In order to determine the effects of floating dust weather conditions on grape photosynthesis and leaf water potential in the Karakash River Basin and on the adaptability of different grapevine varieties to the local climatic conditions, a study was conducted based on the analyses of the occurrence of floating dust weather during 2011-2017 in Karakax County in Karakash River Basin. Using 'Hotan Red', 'Munake', 'Thompson' and 'Centennial Seedless' as experimental materials, the effects of spring floating dust weather and natural cover of dust on photosynthesis and water potential of grape leaves were analyzed. The results showed that the floating dust days in Karakax County during the period from April to May were up to 23.7 days, accounting for 38.9% of the whole period. For floating dust days, average photosynthetically active radiation (PAR) in the area declined by 71.8% at 10:00-20:00 local time during day time. Also net photosynthetic rate (P_n) of grape leaf decreased significantly for all varieties at afternoon (12:00 local time), except for "Munake". For sunny days, the trend in water potential of grape leaf first increased before decreasing later. Leaf water potential change was non-obviously different during floating dust days and was lower than for sunny days. The change in transpiration rate (T_r) in floating dust days was similar to that in sunny days, but with a slight delay. Grape leaf was covered by dust during continuous dusty weather. The amount of dust retention per unit area of canopy of 'Thompson' and 'Centennial Seedless' were respectively 8.64 g·m^-2 and 10.93 g·m^-2. Dust cover dropped significantly P_n in 'Thompson' and 'Centennial Seedless', but increased intercellular CO₂ concentration (C_i). Dust cover also increased saturation intensity, compensation point, intrinsic quantum efficiency, apparent quantum yield and dark respiration rate of leaves of 'Thompson' and 'Centennial Seedless'. Conclusion therefore, dusty weather conditions reduced photosynthetically active radiation intensity, with grape leaves covered in dust, further reducing leaves P_n. At the same time, dust cover significantly increased dark breathing rate. The study suggested that cleaning dust on the surface of grape leaves effectively improved photosynthesis. Under floating dust weather conditions, grape leaf T_r decreased and leaf water potential was maintained. Thus floating dust weather conditions in Karakash River Basin delayed spring water deficit, and alleviated the conflict between supply and use of water in the area.