LIGHT INTERCEPTION EFFICIENCY OF THE UNDERSTORY PALM CALYPTROGYNE GHIESBREGHTIANA UNDER DEEP SHADE CONDITIONS

The tropical rain forest understory palm, Calyptrogyne ghiesbreghtiana Linden ex H. Wendl. (Arecaceae), exploits forest microhabitats characterized by dense shade conditions. In plants exploiting light-limited environments natural selection has shaped the architecture and pattern of leaf display to increase the efficiency of light interception. The optimal strategy of leaf display is to maintain a minimal overlap while keeping the display angles of the physiologically active leaves close to the horizontal, thus increasing the chances of maintaining a positive carbon balance. To measure the efficiency of leaf display in light interception, and determine how plant architecture and leaf display adjust to deep shade in reproductive individuals of C. ghiesbreghtiana under a narrow range of shade conditions, we randomly sampled 20 palms located under primary forest in Braulio Carrillo National Park, Costa Rica. We measured crown structure and efficiency of light interception, calculated as the proportion of the difference between total effective leaf area (horizontal projection of the leaf blade) and overlapped leaf area relative to the total leaf area of the plant. Within the sampled height range (0.6-2.0 m) we found an average of 12 leaves per plant. Leaves were large (0.26 m2, S.D. = 0.08), arranged in spiral and distributed homogeneously around the stem. The average efficiency of light interception was high (93.88%, S.D. = 8.6%, range = 67-100%) compared with efficiencies reported in previous studies for other understory palms. The number of overlapped leaves and total overlapped area increased with the total number of leaves, showing that the plant must continuously adjust its architecture of leaf display (produced in a different light environment) to accommodate for increased leaf area. This type of architecture (spirally produced leaves) could be the most effective response under the intense shade conditions of forest understories. Resumen. La palma de sotobosque del bosque humedo tropical Calyptrogyne ghiesbreghtiana Linden ex H. Wendl. (Arecaceae), ocupa microhabitats caracterizados por condiciones de sombra profunda. En plantas de ambientes limitados en luz, la seleccion natural ha modificado la arquitectura de la planta y el patron de despliegue foliar para aumentar la eficiencia en la intercepcion luminica. La estrategia optima de despliegue de hojas consiste en mantener un traslape minimo, y a la vez, mantener los angulos de despliegue de las hojas fisiologicamente activas cercanos a la horizontal para mantener un balance carbonico positivo. Para medir la eficiencia del despliegue foliar en la intercepcion de la luz, y determinar como la arquitectura de la planta y el despliegue foliar se ajustan a condiciones de sombra profunda en C. ghiesbreghtiana, muestreamos al azar 20 individuos reproductivos a lo largo de un rango estrecho de condiciones de sombra en el bosque primario del Parque Nacional Braulio Carrillo, Costa Rica. Medimos la estructura de la copa y la eficiencia en la intercepcion de luz, calculada como la proporcion de la diferencia entre el area total efectiva (proyeccion horizontal de la lamina foliar) y el area foliar traslapada con relacion al area foliar total de la planta. Dentro del rango de alturas muestreado (0.6-2.0 m) encontramos un promedio de 12 hojas por planta. Las hojas de gran tamano (0.26 m 2