Maintenance and Hysteresis of Soil-Root Interface Water Potential of Cherry-Plum in Response to Soil Dehydration and Rehydration

Abstract

Soil-root interface water potential (Ψ_s·r) of a dry soil indicates the water status at the interface between the soil and the root, but it cannot be easily measured although it is proposed as an appropriate indication of plant water stress. Using an equation of Ohm's analog, we estimated Ψ_s·r and examined the maintenance and hysteresis of Ψ_s·r as well as xylem water potential (Ψ_X) and transpiration rate (E_A) in response to soil dehydration and rehydration for cherry-plum plants (Prunus×cistena) grown in three artificial soil mixes. These mixes were made of composted bark, peat, and sand (Mix-1), peat, bark, sand, and compost (Mix-2), and peat, sawdust, and sand (Mix-3). When water was withheld and the soil matric potential (Ψ_m) was lowered, plants grown in Mix-2 maintained higher Ψ_s·r as well as higher Ψ_X. However, when the soil mix was rehydrated, Ψ_s·r was always lower during the re-wetting than during the drying cycles. The relationship between Ψ_m and Ψ_s·r showed a strong hysteresis-like behavior. Hysteresis was the largest in Mix-2 and the smallest in Mix-3. Hysteresis of Ψ_X or E_A showed a similar trend to that of Ψ_s·r. The differences among soil mixes in hysteresis of Ψ_s·r might be related to the unsaturated hydraulic conductivity of substrates.