Strawberry plants were grown in controlled-environment cabinets with different day-and-night relative humidities, in nutrient solutions of different osmotic potential and different calcium concentrations.Leaf calcium (% d. wt.) depended strongly on leaf age and was lowest and very sensitive to environment when the leaf was emerging from the bud. Calcium in the emergent leaf was greatest and tipburn least when plants were grown in humid nights (VPD usually < 100 Pa) and weak nutrient solutions (osmotic potential about -25 kPa). Such plants guttated freely. In contrast plants grown in dry nights (VPD, c. 600 Pa) never guttated, had small concentrations of calcium in emergent leaves and suffered tipburn. The behaviour of plants transferred between humidity treatments rapidly reflected the new conditions. Increasing the osmotic potential of the nutrient increased tipburn and decreased calcium in emergent leaves even though the nutrient contained more calcium.When the calcium concentration in the emergent leaf exceeded 0.07 per cent of d. wt, tipburn was never seen; below 0.05 per cent tipburn was usually severe.These results suggest that pre-emerged, and therefore non-transpiring, leaves depend for their calcium on water flow arising from root pressure at night. After leaf emergence, calcium intake into leaves was promoted by dry days, indicating that calcium was then supplied by transpirational water flow. Humid nights, dry days and weak nutrient solutions minimize the risk of leaf tipburn in strawberry. © 1979, Annals of Botany Company.
