The adaptation to temperature of photorespiration and of the photosynthetic carbon metabolism of altitudinal ecotypes of Trifolium repens L.

In altitudinal ecotypes of Trifolium repens L. the oxygen inhibition of photosynthesis, the CO2 compensation point and the sugar content were examined. Excised leaves were exposed to 14CO2 for 20 s and 60 min periods and the radioactivity in different photosynthetic products was studied. In all experiments the temperature during growth and measurement was varied.To some extent, the differences between the ecotypes and the differences between the plants grown under different temperature conditions are similar. These ecotypic differences appear to reflect long-term adaptation to the general temperature conditions at each site. Alpine ecotypes and plants grown at low temperatures show an increased photorespiration. The 14C-labeling of certain photosynthetic products also changes with the ecotypes and the temperatures during growth. Other differences between the ecotypes are interpreted as adaptations to the partial pressure of Co2 and to the length of the growing season, both of which change with altitude.The metabolism of photosynthesis depends greatly on temperature. The 14C-experiments and the study of photorespiration suggest that, to a certain degree, adaptation can compensate for this dependence on temperature.