Soil Chemical Properties Strongly Influence Distributions of Six Kalidium Species in Northwest China

The degrees of adaptive responses of different halophytes to saline–alkali soil vary substantially. Kalidium (Amaranthaceae), a genus comprised of six species of succulent euhalophytes with significantly differing distributions in China, provides ideal material for exploring the ecophysiological relationships involved in these variations. Thus, in a large-scale field survey in 2014–2018, samples of soil (at 20 cm depth intervals spanning 0 to 100 cm) and seeds were collected from areas where these six species are naturally distributed. Chemical properties of soils in the areas and germinability of the species’ seeds in media with 0–500 mM NaCl and 0–250 mM Na2SO4 were then analyzed to test effects of salinity-related factors on the species’ distributions. The pH of the soil samples mainly ranged between 8.5 and 10.5 and positively correlated with their mean total salt contents. Germination rates of all six species’ seeds were negatively correlated with concentrations of NaCl and Na2SO4 in the media, and their recovery germination rates in distilled water were high (>74%). The results show that the species’ distributions and chemical properties of their saline soils are strongly correlated, notably the dominant cation at all sites is Na+, but the dominant anions at K. cuspidatum and K. caspicum sites are Cl− and SO42−, respectively. Species-associated variations in concentrations of Ca2+ were also detected. Thus, our results provide clear indications of major pedological determinants of the species’ geographic ranges and strong genotype-environment interactions among Kalidium species.