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

Abstract

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.