Dependence of Calcium Transport into Strawberry Leaves on Positive Pressure in the Xylem

Strawberry plants were cultured in concentrated and dilute nutrient solutions by day and night, factorially. Guttation decreased, leaf tipburn increased and calcium in emerging leaves was reduced when solutions were more concentrated at night. Nutrient concentration in the daytime was much less important for these responses. The effects were similar when the more concentrated solution contained additional Ca2+, NO2−, Cl− and SO42− or extra of all the major nutrients in the same proportions. When the solution was made stronger by adding extra Mg2+, NO2−, Cl− and SO42− the guttation, tipburn and calcium differences were basically similar to those in the previous experiment but with an added effect explained by a competitive suppression of calcium uptake caused by the extra magnesium. Thus, both nutrient strength and cation balance are important for preventing strawberry leaf tipburn. The results accord with the hypothesis that calcium translocation into pre-emerged strawberry leaves depends on the attainment of a positive water pressure in the xylem at night, when transpiration losses are minimal.