Photosynthetic 14CO2 fixation products in altitudinal ecotypes of Trifolium repens L. with different temperature requirements.

Two Trifolium repens clones from natural meadows at 600 m and 2030 m above sea level, and with differing dependence on temperature of their rate of apparent photosynthesis, were grown under controlled environments. Radioactive products in detached leaves were examined after 20 and 40 s periods of steady state photosynthesis in 14CO2 at 3° C and 24° C. Glycine and serine were hardly labeled at 3° C. At 24° C, the leaves of the alpine clone showed significantly, (P<0.025) more activity in these amino acids than those from the low altitude clone. It is suggested that the alpine clone has a higher photorespiration. This is supported by the labeling pattern of glucose, fructose, sucrose, and glucose-6-phosphate.The high altitude clone requires lower temperatures for photosynthesis than the low altitude clone. It is suggested, that this is caused by its higher photorespiration, which reduces net photosynthesis at high temperatures. The lower photorespiration activity of the low altitude clone can be interpreted as an adaptation to its warmer habitat.