Effect of soil water osmotic potential on growth and water relationships in barley during soil water depletion

Summary

Barley plants (Hordeum distichum, L., cv. ‘Zita’) grown in a sandy soil in pots were adjusted during a pretreatment period of 5 days to three levels of soil water osmotic potential by percolating 61 of a nutrient solution with additional 0, 22.3 and 44.6 mM KCl. A drying cycle was then started and the plants were harvested when the soil water matric potential had decreased to −1.4 MPa, respectively 6, 7 and 8 days later.

No significant differences in dry matter yields, transpiration coefficients and wilting percentages were found between treatments.

During the drying cycle leaf water potential (ψ _l ) decreased concomitantly with decrease in soil water potential (ψ _s ) with almost constant and similar differences (ψ _l −ψ _s ) for all treatments despite differences in levels of potentials. The concomitant decrease in leaf osmotic potential (π) was due partly to dehydration (58%) and partly to increase in leaf solute content (42%) independent of treatment. The part of total osmotic solutes due to K decreased relatively during the drying cycle.

Close relationships were found between π and ψ _l as functions of relative water content (RWC). Identical curves for the two levels of salt treatment agree with similar concentrations of K, Cl, and ash found for salt treated plants indicating that maximum uptake of macro nutrients may have been reached.

During the main part of the drying cycle the turgor potential as function of RWC was higher and decreased less steeply with decreasing RWC in the salt treated than in the non-salt treated plants.

In the beginning of the drying cycle additions of KCI lowered the transpiration rates of the salt treated plants resulting in a slower desiccation of the soil and hence an increased growth period. A delay in uptake from a limited soil water supply may be advantageous during intermittent periods of drought.