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Survival strategies of Ammopiptanthus mongolicus and Zygophyllum xanthoxylon in saline and drought environments, northwest China

100%

Shen X. , Chai M. , Xiang J. , Li R. , Qiu G.

tom 37

nr 10

Ammopiptanthus mongolicus and Zygophyllum xanthoxylon are typical plants in the West Ordos National Natural Reserve of Inner Mongolia, China. The populations of A. mongolicus had few young individuals and senesced. However, Z. xanthoxylon was growing well in the habitat of A. mongolicus. In addition, there is little information to compare their seed germination and seedling growth under combined salt and drought environments. In order to exploring the reason for the actuality, a study was conducted to quantify the interactive effects of salinity and drought stresses on seed germination and seedling growth of A. mongolicus and Z. xanthoxylon and then to compare the survival strategies of both shrubs. The experiment consisted of seven gradient concentrations of salinity (0, 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8 % NaCl) in each of the six drought stress levels (0, -0.2, -0.4, -0.8, -1.6 and -2.0 Mpa polyethylene glycol). As expected, combined salinity and drought stresses had significant (P\0.05) interactive effects on seed germination of the two tested shrubs. There was significant decrease in these indices, in response to increased salt and/or drought stresses. The higher germination rate and shorter germination duration were detected for A. mongolicus, which may lead to the loss of seed bank. In addition, the radicle length of A. mongolicus (0–2.3 cm) was shorter than that of Z. xanthoxylon (0–14.6 cm), indicating less resistance of seedlings to the volatile conditions in the surface of arid soil. The stepwise regression analysis showed that salinity was the dominant influencing factor and followed by drought in seed germination and seedling growth under salt–drought mixed stress.

Effects of saline-alkaline stress on early growth strategy and colonization success of Flaveria bidentis ( L.) Kuntze (Asteraceae ) - a new exotic plant in Northern China

86%

Chai M. , Shi F. , He K. S. , Li R. , Cao D. , He Z.

tom 60

nr 3

Flaveria bidentis, an annual grass native to South America, has invaded into many countries all over the world, including South Africa and Egypt in Africa, Britain and France in Europe, Japan in Asia, and Australia. In China, this plant species has been widely distributed in Hebei province since 2001 of its first discovery in Tianjin. In salinized soil of northern China, F. bidentis has formed mono dominant communities owing to its opportunistic characteristics. In this study, we investigated germination rate, germination energy, germination index and vigor index in response to different saline-alkaline stresses. Lengths of seedling, hypocotyl, and radicle were also examined. During germination process, germination rate, germination energy, germination index, and vigor index decreased due to higher salinity and alkalinity (pH). Hypocotyl elongation was stimulated at low salinity and alkalinity, but decreased with increasing salinity and alkalinity. The lengths of radicle and seedling were inhibited sharply with increasing salinity and alkalinity. These results suggest that a reciprocal enhancement between salt stress and alkaline stress was a characteristic feature during seed germination of F. bidentis. Ungerminated seeds resumed to germinate after transferred to distilled water, indicating that seeds remained viable during their exposure to saline-alkaline stresses. Stepwise regression analysis indicated that the effects of salinity, alkalinity (pH), and buffer capacity on seed germination and seedling growth were significantly different in magnitude. Salinity and alkalinity (pH) were the dominant factors in seed germination and seedling growth of F. bidentis respectively. burther, the results of this study suggest that F. bidentis has developed excellent adaptative strategy in its early stage of life cycle which partially explains its current invasion success in northern China.