XVI International Botanical Congess

Native Heteropogon contortus populations are declining in Hawaii, and many remaining grasslands appear threatened by invasion of alien Pennisetum setaceum. This study compared the reproductive response of these grasses to varying water and nutrient levels to determine conditions that give P. setaceum a reproductive advantage. Plants were grown from seed in a greenhouse under two levels of water and nutrients. Heteropogon contortus flowered under all treatments, but produced more inflorescences when fertilized. Pennisetum setaceum flowered only under high nutrient levels. In low water conditions, P. setaceum inflorescences failed to mature seeds, while H.contortus produced seeds even at low water and nutrient levels. The invader, P. setaceum, appears to require higher resource levels than the native, H. contortus, for flower and seed production.