A rapid demonstration of the self-thinning rule using radish

Abstract

The self-thinning rule describes the relationship between individual mass and density in crowded evenly-aged plant populations in which the slope of the relationship is always greater than -1. This study investigated whether the rule could be demonstrated in six weeks using radish (Raphanus sativa L.) grown in trays (0.033 m²) in a greenhouse. Seeds of a radish cultivar were sown in a 4:2:1 mixture of sand, potting soil and compost and watered twice daily to field capacity. One week later, seedlings in each tray were thinned out to one of 19 densities ranging from 4 to 64 individuals. Thereafter, the radishes were left to grow for a further five weeks under the same watering regime and then harvested. The log-log regression of average fresh mass against density produced a slope of −0.76 which deviates significantly from the expected −4/3 power rule. This result indicates that initial plant densities need to be higher if the self-thinning rule is to be demonstrated successfully.