Leaf water relations characteristics of differently potassium fertilized and watered field grown barley plants

Seasonal leaf water relations characteristics were studied in fully irrigated spring barley (Hordeum distichum L. cv. Gunnar) fertilized at low (50 kg K ha⁻¹) or high (200 kg K ha⁻¹) levels of potassium applied as KCl. The investigation was undertaken from about 14 days before anthesis until the milk ripe stage in leaves of different position and age. Additionally, the effects of severe water stress on leaf water relations were studied in the middle of the grain filling period in spring barley (cv. Alis). The leaf water relations characteristics were determined by the pressure volume (PV) technique. Water relations of fully irrigated plants were compared in leaf No 7 with the water relations of slowly droughted plants (cv. Alis). Leaf osmotic potential at full turgor (ψ _π ¹⁰⁰ ) decreased 0.1 to 0.3 MPa in droughted leaves indicating a limited osmotic adjustment due to solute accumulation. The leaf osmotic potential at zero turgor (ψ _π ⁰ ) was about −2.2 MPa in fully irrigated plants and −2.6 MPa in droughted plants. The relative water content at zero turgor (R⁰) decreased 0.1 unit in severely droughted leaves. The ratio of turgid leaf weight to dry weight (TW/DW) tended to be increased by drought. The tissue modulus of elasticity (ε) decreased in droughted plants and together with osmotic adjustment mediated turgor maintenance during drought. A similar response to drought was found in low and high K plants except that the R⁰ and ε values tended to be higher in the high K plants. Conclusively, during drought limited osmotic adjustment and increase in elasticity of the leaf tissue mediated turgor maintenance. These effects were only slightly modified by high potassium application. The seasonal analysis in fully irrigated plants (cv. Gunnar) showed that within about 14 days from leaf emergence ψ _π ¹⁰⁰ decreased from about −0.9 to −1.6 MPa in leaf No 7 (counting the first leaf to emerge as number one) and from about −1.1 to −1.9 MPa in leaf No 8 (the flag leaf) due to solute accumulation. A similar decrease took place in ψ _π ⁰ except that the level of ψ _π ⁰ was displaced to a lower level of about 0.2 to 0.3 MPa. Both ψ _π ¹⁰⁰ and ψ _π ⁰ tended to be 0.05 to 0.10 MPa lower in high K than in low K plants. R⁰ was about 0.8 to 0.9 and was independent of leaf position and age, but tended to be highest in high K plants. The TW/DW ratio decreased from about 5.5 in leaf No 6 to 4.5 in leaf No 7 and 3.8 in leaf No 8. The TW/DW ratio was 4 to 10% higher in high K than in low K plants indicating larger leaf cell size in the former. The apoplastic water content (V_a) at full turgor constituted about 15% in leaf No 7. ε was maximum at full turgor and varied from about 11 to 34 MPa. ε tended to be higher in high K plants. Conclusively, in fully watered plants an ontogenetically determined accumulation of solutes (probably organic as discussed) occurred in the leaves independent of K application. The main effect of high K application on water relations was an increase in leaf water content and a slight decrease in leaf ψ_π. The effect of K status on growth and drought resistance is discussed.