Photosynthesis and Respiration of Maize Seedlings at Suboptimal Temperatures

Growth of maize seedlings is limited by low temperature and ceases at about 10 °C. In a search for processes underlying this limitation, rates of photosynthesis and dark respiration were measured in controlled environments at night/day temperatures of 5/10, 10/15, and 15/20 °C. CO2 exchange was measured on whole seedlings including the root system. Two maize hybrids, which differed in dry matter production at low temperature, were tested from the 4th-leaf until the 8th-leaf stage. Gross photosynthesis, net photosynthesis, and respiration increased proportionally with leaf area. The response to low temperature was independent of seedling stage. The decline of photosynthesis and respiration with decreasing temperature was similar in both hybrids. At 10 °C, rates of photosynthesis and respiration were relatively high indicating a minimum temperature for those processes much lower than 10 °C. Possible reasons for growth limitation at 10 °C are discussed.