CANOPY PHOTOSYNTHESIS AND RESPIRATION IN WINTER-WHEAT ADAPTED AND UNADAPTED TO CONNECTICUT

How is seasonal variation in photosynthesis and respiration related to adaptation of winter wheat (Triticum aestivum L.) to the climate of the U.S. Northeast? Canopy CO2 exchange rates were measured from stem elongation through grain filling for six cultivars and correlated with biomass, harvest index, and yield. Four cultivars were bred in other climates: Avalon in England, Hart and Pike in Missouri, and Yamhil in Oregon. Houser and Ticonderoga were high-yielding cultivars bred in New York. On average, yield was 73% greater in 1986 than in 1987, but only Hart and Houser changed rank between years. In 1986, Pike and Hart had yields similar to Houser and Ticonderoga. Yields of Avalon and Yamhil were substantially less. Over both years, high grain yield was correlated with high leaf area before heading, R = 0.8. Yield was correlated both with rapid canopy photosynthesis and rapid dark respiration per unit ground area from heading to anthesis, R = 0.7. Apparent maximum photosynthesis per unit leaf area (P0) and apparent light-use efficiency (alpha) were extrapolated from the irradiance response of canopy photosynthesis. The P0 was greatest for Houser across all measurements, and least for Hart and Yamhil. During grain fill in 1986, alpha was greatest for Houser and Ticonderoga, and over both years, alpha was correlated with yield. Per unit ground area, canopy dark respiration was least for Yamhil; per unit shoot dry weight, respiration was greatest for Avalon. These results suggest adaptation to the climate of the U.S. Northeast was related to a high leaf area index during stem elongation, rapid canopy photosynthesis and respiration between heading and anthesis, and high photosynthetic efficiency during grain filling.