Effect of temperature on light utilization efficiency of leaves in C3 legumes and C 4 grasses

The effect of temperatures between 15 and 50°C on the light utilization efficiency of leaf net photosynthesis was studied in two C4 grasses and two C3 legumes. In the legumes, light utilization efficiency (μ mol of CO2 fixed per μ Einstein of incident photosynthetic quantum flux) declined linearly with temperature between 15 and 45°C. On the other hand, it was independent of temperature between 15 and 40°C in the grasses, but it declined rapidly between 40 and 50°C. Values for grasses were greater than those for legumes at all temperatures; for example, at 30°C the ratio of the mean values of grass to legume was 1.6-1.7 which is similar to a previously published value of 1.6. Light utilization efficiency was similar for grasses and legumes only at temperatures below 10 and above 50°C. These findings are compared with published data, especially those of Ehleringer and Björkman, and their implications for predicting or interpreting the distribution of C3 and C4 species are briefly discussed.