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.
Division of Tropical Crops and Pastures, CSIRO, Mill Road, 4067, St Lucia, Queensland, Australia.
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Ludlow