| Desertification is a serious problem in arid and semi-arid regions in China. According to the third monitor of desertification, 2,636,200Km~2 of land area is desertified, about 27.46% of the total land area of China. Desertification has an adverse effect on social and economic development of northwest regions of China.Zygophyllum xanthonylon is a succulent shrub growing in the Alxa Desert of China. In the low salt and arid environments, Z. xanthonylon absorbed sodium and transported sodium into aboveground parts, which may be a main strategy that Z. xanthonylon adapted to drought stress. However physiological functions of sodium in plants under drought stress conditions are still unclear. In this study, the physiological functions of sodium in growth and drought resistance of succulent xerophytes, Z. xanthonylon were investigated by sand and pot culture. The main results were as following:1. The low concentration of sodium(5~100mmol/L) stimulated the growth of Z. xanthonylon, and 50mmol/L NaCl was optimum concentration for the growth of Z. xanthonylon, compared with the control, fresh weight of leaves, stems and roots increased by 104%, 57% and 149% (P<0.05), respectively, Dry weight by 34%, 51% and 65% (P<0.05), water content by 52%, 35% and 17% (P<0.05), respectively. At the same time, MDA content and relative penetrability of membrane decreased significantly (P<0.05), succulent degree of leaves and relative organic dry weight increased. During treatment with 300mmol/L NaCl solution, compared with the control, fresh weight decreased by 19.3% and 38% (P<0.05) for leaves and roots of Z. xanthonylon, respectively, and relative penetrability of membrane and MDA content increased significantly (PO.05).2. Under the different osmotic stress (-0.5, -1.0和-1.5MPa), 50mmol/L NaCl alleviated growth inhibition of Z. xanthonylon caused by drought stress, fresh weight and water content increased significantly (P<0.01) . Under the low-grade stress (-0.5MPa), water content and organic dry weight of plant increased by 201% and 30% (P<0.05).3. Under the identical osmotic stress (-1.0MPa), with the increase of sodium concentrations, the ability for Z. xanthonylon to adapt to drought stress was enhanced. Compared with treatment without NaCl(0mmol/L), fresh weight increased by 103%, 177%, 186% and 131% (P<.01) for leaves of Z. xanthonylon during treatments of 5, 50, 100 and 200mmol/L NaCl, respectively. Accordingly, fresh weight increased by26%, 83%, 157% and 22% (PO.05) for stems of Z. xanthonylon, respectively. No significant difference in root fresh weight was observed during treatments of 5, 100 and 200mmol/L NaCl (P>0.05), except for root fresh weight decrease of 48% (P<0.05) during treatment of 200mmol/L NaCl. With NaCl concentrations increase, relative penetrability of membrane and MDA content decreased significantly (PO.05).4. In the pot culture, NaCl also alleviated growth inhibition of Z xanthonylon caused by drought stress. Compared with the drought treatments, fresh weight increased by 35% and 45%(P<0.05 )for stems and roots, dry weigh increased by 18%, 37% and 37% (P<0.05) for leaves, stems and roots under treatments of NaCl (50mmol/L) and drought.
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