Osmotic adjustment and energy limitations to plant growth in saline soil

Summary Plant roots must exclude almost all of the Na + and Cl – in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c . 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium. Taking up just 2% of the NaCl allows a plant to osmotically adjust the Na + and Cl – in vacuoles, while organic solutes provide the balancing osmotic pressure in the cytoplasm. We quantify the costs of this exclusion by roots, the regulation of Na + and Cl – transport through the plant, and the costs of osmotic adjustment with organic solutes in roots.