Testing seed germination responses to water and salinity stresses to gain insight on suitable microhabitats for restoration of cold desert shrubs

Although congeneric species grow in the same desert, responses of their seeds to water and salinity stress may differ, thus resulting in variation in microhabitats that are suitable for restoration. Experiments were performed to determine seed germination responses to water limitation and salinity stress (imposed by increasing concentrations of polyethylene glycol (PEG) and sodium chloride (NaCl), respectively) of Nitraria tangutorum and Nitrariasibirica, two xerophytic and halophytic shrubs in the cold deserts of northwest China. Germination percentages of both species decreased with a decrease in PEG water potentials. The lowest PEG water potential for germination was -0.9MPa for N.tangutorum and -1.5MPa for N.sibirica. All concentrations of NaCl had negative effects on germination of N.tangutorum seeds, whereas germination of N.sibirica was promoted under low salinity (-0.3MPa NaCl). The lowest osmotic potential of NaCl solutions under which seeds could germinate was -1.2MPa for N.tangutorum and-1.8MPa for N.sibirica. These germination responses to water limitation and salinity generally were correlated with the ecological distribution of the two species in the desert and indicate that seeds of N.sibirica potentially would germinate in more stressful microhabitats than those of N.tangutorum.