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Soil salinization in arid zones is a major factor that resulted in the reduction in the yield and quality of many important crops in Northwestern China. In this study, the potential mechanism of flue gas desulfurization gypsum by-product (FGDB) mediated amendment of alkaline soils was investigated in an oil sunflower model by accessing the Ca2+ distribution and Ca2+-ATPase activity in leaf cells. Our results demonstrated an increased calcium concentration, as well as intact chloroplast structure with increasing calcium precipitates in the cell wall, intercellular space, and vacuole of leaf cells in the plants grown in alkaline soils supplied with FGDB or CaSO4. Additionally, a dose-dependent Ca2+-ATPase activity was detected in the plasma membrane and tonoplast of leaf cells from the plants grown in FGDB or CaSO4 supplemented soils. These results implied that the Ca2+- ATPase activity cause cytosolic Ca2+ efflux. The Ca2+ influx is through the Ca2+-channels, and increasing cytosolic Ca2+ concentration might benefit the stability and integrity of cell membrane and cell wall, sequentially alleviated the injury of oil sunflower against alkali stress. [ABSTRACT FROM AUTHOR]