Organic Solute Accumulation and Dehydration Tolerance in Three Water-Stressed Populus deltoides Clones

The relationship between osmotic potential, water-soluble organic solutes and electrolyte leakage was investigated in three greenhouse-grown eastern cottonwood (Populus deltoides Barn.) clones. The Ohio Red (from southern Ohio) and Platte (from eastern Nebraska) clones were selected because they differ in dehydration tolerance, gas exchange and osmotic potential. A third clone, Wildcat (from western Nebraska) was included because of its origin in a very dry area. Plants were either watered daily (control) or watered every 4-6 days (preconditioned). A third group of plants was watered daily until it was water-stressed at the end of the experiment (nonconditioned). Leaves for osmotic potential and watersoluble solute determinations were sampled at predawn after plants were rewatered. All clones showed osmotic adjustment ranging from 0.23 to 0.48 MPa. Organic solutes contributed up to 48% of the total osmotic adjustment. The solutes that contributed at least -0.05 MPa each to leaf osmotic potential in any clone were sucrose, malic acid, glucose, fructose, myoinositol and salicin. Fructose and glucose concentrations were unchanged or declined in preconditioned Ohio Red and Platte but increased in Wildcat. The Ohio Red clone had the highest sucrose concentration in both well-watered and preconditioned plants, and a lower injury index (more membrane stability) than Wildcat in the preconditioned plants, whereas nonconditioned Platte displayed the greatest electrolyte leakage of all clones and treatments. Cell membrane stability was correlated to osmotic potential and sucrose concentration only in Ohio Red.