Seasonal changes in photosynthetic activity of snow tussocks (Chionochloa spp.) along an altitudinal gradient in Otago,New Zealand

Summary Photosynthetic characteristics were studied in Chionochloa rigida, an altitudinally widespread snow tussock and a closely related high-altitude species C. macra. Along a gradient from near sea level to 1600 m there were no consistent differences in maximum photosynthetic capacity which averaged 4.5 mol CO₂ m^-2s^-1. The photosynthetic temperature optimum ranged between 15 and 18°C and there was only a limited capacity for seasonal adjustment. Net photosynthesis was light-saturated at about 500 mol photons m^-2s^-1. In winter, the photosynthetic capacity decreased significantly with increasing altitude of origin of the snow tussocks. A transplant experiment indicated this was partly genetically controlled.