Maintenance and hysteresis of soil-root interface water potential of cherry-plum in response to soil dehydration and rehydration

Soil- root interface water potential (psi(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 psi(s).(r) and examined the maintenance and hysteresis of psi(s).(r) as well as xylem water potential (psi(x))and transpiration rate (E-A) in response to soil dehydration and rehydration for cherry- plum plants (Prunus x cistena) grown in three artificial soil mixes. These mixes were made of composted bark, peat, and sand (Mix-l), pear, bark, sand, and compost (Mix-2), and peat, sawdust, and sand (Mix-3). When water was withheld and the soil matric potential (psi(m)) was lowered, plants grown in Mix-2 maintained higher psi(s).(r) as well as higher psi(x). However, when the soil mix was rehydrated, psi(s).(r) was always lower during the re-wetting than during the drying cycles. The relationship between psi(m) and psi(s).(r) showed a strong hysteresis-like behavior. Hysteresis was the largest in Mix-2 and the smallest in Mix- 3. Hysteresis of mu(x) or E-A showed a similar trend to that of psi(s).(r). The differences among soil mixes in hysteresis of psi(s).(r) might be related to the unsaturated hydraulic conductivity of substrates.