Optimal leaf display and biomass partitioning for efficient light capture in an understorey palm, Licuala arbuscula

1. The effects of leaf display and biomass partitioning on light capture efficiency were examined in a non-branching understorey palm, Licuala arbuscula, by using a three-dimensional geometric simulation model. This species has several fan-shaped laminae, attached on long petioles at a mostly constant deflection angle (D-P). The petiole of the youngest leaf was almost vertical, and slanted downwards as it aged. 2. The combination of large D-P and small Z(max) (zenith angle of the oldest leaf's petiole) maximized light capture for a plant with few leaves; this combination kept the lamina facing in the approximate direction of the zenith with high light intensity. For a plant with many leaves, the combination of large Z(max) and small D-P increased light capture because it reduced self-shading. 3. For a given total leaf biomass, the plant increased its total leaf area by producing many small leaves. This occurred because the leaf area per unit biomass decreased with increasing biomass per individual leaf. This effect was most pronounced in larger plants. However, an increasing number of leaves intensified self-shading among leaves. Allocation of biomass to the petioles reduced self-shading, but decreased leaf area. 4. There was an optimal allocation of biomass to petioles and an optimal number of leaves that maximized the crown's light capture. Greater investment in petioles as the number of leaves increased was the favoured strategy for larger plants. 5. In most cases, the leaf geometry and biomass partitioning in the plants were close to the optima predicted by a simulation model developed in this study. There were noticeable differences in a few cases, but the reduction in the crown's light capture due to these differences was small.