Eco-physiological studies of the semiarid grasses Aristida leptopoda and Astrebla lappacea

The perennial grasses (Aristida spp.) are invaders of the Mitchell (Astrebla spp.) grasslands of semiarid Queensland. The possible role of a number of physiological factors influencing the establishment and maintenance of Aristida leptopoda (white spear grass) and Astrebla lappacea (curly Mitchell grass) populations were examined in a series of experiments. Under controlled conditions, both seedling growth and root extension rates of curly Mitchell grass were far superior to white spear grass at a temperature of 30°C. However, at temperatures of 25°C and less, little species differences in these rates occurred White spear required a lower soil phosphorus concentration for optimum growth compared with curly Mitchell grass, but its yield response to increasing phosphorus concentration was much smaller than this species. Results of other studies suggested that relative drought endurance of established plants of these species to be related more to the amount and vertical distribution of the root system rather than to differences in stomatal control.