The Relationship Between Plant Water Potential and Transpiration Rate in Young Cabbage Plants Growing in Wet Soil

Water potentials in the plant stem were monitored together with transpiration rates in young cabbage plants growing in pots of soil and subjected to cyclic transpirational demands. When the soil was very wet plant water potential was approximately proportional to transpiration rate. At lower soil water contents water potentials remained almost constant despite considerable changes in transpiration rate. When the transpiration rate was high, water potentials in plants were lower in wet soil than in soil having a slightly lower moisture content. It is argued that the results can best be explained in terms of root conductivity increasing as the plant becomes more water stressed when the gradient between soil and plant water potentials steepens.