Effects of Temperature on Photosynthesis by Maize and Wheat

Abstract

Maize and wheat plants were grown in controlled environments with day temperatures of 13, 18, 23, or 28 °C. Leaves from maize grown at 23 °C photosynthesized faster than leaves from maize grown at 13 or 18 °C and, except when measured at 28 °C, faster than leaves from maize grown at 28 °C;leaves of maize grownat 13 °C were yellow and photosynthesized at insignificant rates. Leaves from wheat grown at 18 ° or 13 °C had faster rates of photosynthesis than leaves from wheat grown at 23 or 28 °C. The best rates for maize were faster than the best rates for wheat when the measurements were made at 23 or 28 °C but at 13 or 18 °C the best rates for maize were not significantly better than the best rates for wheat. Leaves of maize that developed in the environment with 23 °C as the day temperature did not rapidly lose their green colour when transferred to the environment with the day temperature of 13 °C and the rate of photosynthesis of these leaves did not decline rapidly. However, new leaves expanding in the cooler conditions were yellow and not effective in photosynthesis. At 13 or 18 °C maize, a C4 plant, which photorespires slowly, did not photosynthesize more effectively than wheat, which photorespires rapidly. The maize did not produce its most effective leaves at 13 or 18 °C and its optimum temperature for photosynthesis was 23°C or higher. It may therefore be considered ill-adapted to the temperate climate.