2007/05/01 by Thomas T. Cochrane, Thomas A. Cochrane
Environmental Science · Engineering · Agricultural and Biological Sciences · #Plant Water Relations and Carbon Dynamics #Soil and Unsaturated Flow #Plant responses to water stress
paper · doi:10.1097/ss.0b013e3180339f92
This article is a follow-up to our recent preliminary findings of how the osmotic potential properties of solutes influence solution flow throughout the soil-plant continuum. The nonempirical equation to calculate osmotic pressure was revised and used to compare a series of organic with inorganic solutes, many of which are found in the soil-plant continuum. Sucrose, acetic acid, creatinine, ethanol, D-fructose, glycerol, D-glucose, lactic acid, maltose, D-mannitol, and urea were compared with NaCl, NH4Cl, CaCl2, MgSO4, HCl, HNO3, KCl, KI, KOH, NaNO3, and NaOH. At a concentration of 0.1 M, the spacing effect on the free solution water by the organic solutes ranged from 56 to 88% of their total osmotic potentials compared with 39 to 53% for the inorganic solutes. However, the water holding capacities of the latter ranged from 39 to 44% vs. 0 to 34% for the organic solutes. At higher concentration levels, the same trends persisted. The calculations show that the osmotic potentials of the organic solutions are largely a function of the size of their solute particles, whereas for electrolytes, the water-holding capacities of ions have a much stronger influence. This confirms that flow along plant sieve tubes can be attributed mainly to the interplay of organic solutes altering the spatial relationships of the free water molecules of phloem solutions; in contrast, the water-holding properties of soil solution ions strongly influence the absorption and subsequent translocation of soil water by plants.