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Keywords:

  • leaf water potential;
  • salt accumulation;
  • salt stress;
  • transpiration;
  • wheat

Abstract

We investigated the effects of continuous salt accumulation in the root zone of wheat. Leaf water potential and transpiration rate were measured in plants grown in an experimental pot system. Plants were grown in a controlled-environment glasshouse in sand-filled pots, in which the groundwater table was maintained at a desired depth. Saline water was recharged from the base, providing constant water content in the unsaturated root zone. At 52 days after sowing, the water table was set at a depth of 47 cm from the soil surface. Groundwater and initial soil water were replaced with saline water with electrical conductivities (EC) of 0.2 dS m−1 (Control [C]), 8 dS m−1 (EC8) and 16 dS m−1 (EC16). The daily transpiration rate, leaf water potential (ψL) and EC of the soil water at a depth of 45 cm were measured during the experiment. Stomatal behavior was expressed using the transpiration ratio Et/Etc (the ratio of the transpiration rates of EC8 and EC16 to that in the control). Our results indicated that ψL and Et/Etc gradually decreased with increasing soil water EC as a result of transpiration and water uptake by the roots. The final ψL values of EC8 and EC16 were –4.0 MPa and –7.0 MPa, respectively, and the final Et/Etc values of EC8 and EC16 were 0.3 and 0.2, respectively. Et/Etc decreased with decreasing ψL, and induced stomatal closure. The Et/Etc of the wheat was 0.5 when ψL was –2.5 MPa and 0.3 when ψL was –3.0 MPa. Although a reduction in ψL from –1.5 MPa to –3.0 MPa caused a steep decline in Et/Etc, a subsequent reduction of ψL to –7.0 MPa caused only a minor reduction. This relationship between stomatal behavior and salt accumulation is similar to that reported in previous studies for plants grown in drought conditions. Changes in the transpiration ratio were expressed in an empirical equation as a function of ψL.