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 a nd seedling relative growth rate (RGR) responses to Na and Psi(s) stress. T he study species. Chrysothamnus nauseosus ssp. consimilis and Sarcobatus ve rmiculatus (hereafter referred to by genus), differ in their distribution a long salinity gradients, with Chrysothamnus inhabiting only less saline are as. In growth chamber studies, declining Psi(s) (-0.82 to -2.71 MPa) inhibi ted germination of both species, and Chrysothamnus was less tolerant of Psi (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 spec ies exhibited ion toxicity. There was substantial ion enhancement for Sarco batus in lower Psi(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 m mol/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 differe nces in seed and seedling Psi(s) stress tolerance probably contribute to th e restricted distribution of Chrysothamnus to less saline areas. The Na upt ake of Sarcobatus seedlings enhances its ability to deal with declining Psi (s) and establish in more saline areas.