Water potential and ionic effects on germination and seedling growth of two cold desert shrubs.

We tested expectations that two desert shrubs would differ in germination and seedling relative growth rate (RGR) responses to Na and Ψ(s) stress. The study species, Chrysothamnus nauseosus ssp. consimilis and Sarcobatus vermiculatus (hereafter referred to by genus), differ in their distribution along salinity gradients, with Chrysothamnus inhabiting only less saline areas. In growth chamber studies, declining Ψ(s) (-0.82 to -2.71 MPa) inhibited germination of both species, and Chrysothamnus was less tolerant of Ψ(s) stress than Sarcobatus. Germination fell below 10% for Chrysothamnus at -1.64 MPa (NaCl and PEG), and for Sarcobatus at -2.4 MPa PEG. Neither species exhibited ion toxicity. There was substantial ion enhancement for Sarcobatus in lower Ψ(s), allowing for 40% germination in -2.71 MPa NaCl. For seedling RGR, species were not different at -0.29 or -0.82 MPa (0 and 100 mmol/L NaCl, respectively), but Chrysothamnus RGR declined substantially at -1.3 MPa (200 mmol/L NaCl). The greater stress tolerance of Sarcobatus was not associated with a lower RGR under nonsaline conditions. Species differences in seed and seedling Ψ(s) stress tolerance probably contribute to the restricted distribution of Chrysothamnus to less saline areas. The Na uptake of Sarcobatus seedlings enhances its ability to deal with declining Ψ(s) and establish in more saline areas.