Temperature, nitrogen, and carbon dioxide effects on spring wheat development and spikelet numbers

Spring wheat (Triticum aestivum L.) responds favorably to elevated atmospheric carbon dioxide concentration ([CO2]) at optimum temperatures. Predictions are for air temperatures to increase as global [CO2] increases. Since spring wheat grain yields generally decline as temperature increases, there is a need to understand the effects of both [CO2] and temperature on spring wheat growth, development, and yield potential. Objectives were to evaluate combinations of [CO2], air temperature, and applied N levels on leaf and apex development, spike components, tiller numbers, dry matter, plant height, and water use in spring wheat. 'Amidon' spring wheat was grown in controlled environment chambers at all combinations of 350, 650, and 950 mu L L(-1) [CO2], 0, 100, and 300 kg N ha(-1), and 14/18 degrees C and 22/26 degrees C night/day air temperatures. Temperature affected the Haun stage by growth degree-days (GDD) relationship more than N or [CO2]. The phyllochron in GDD was greater for plants grown at 22/26 degrees C (433 GDD) than at 14/18 degrees C (345 GDD). The Haun stage at apex double ridge and terminal spikelet increased as applied N and [CO2] increased. Fertile spikelet numbers increased as [CO2] and N level increased at 14/18 degrees C, but at 22/26 degrees C, spikelets increased as N increased and decreased as [CO2] increased. Fertile spikelets were greatest at 14/18 degrees C and 650 mu L L(-1) [CO2]. Results suggest that at elevated [CO2] and adequate soil water, air temperature is more important than [CO2] in controlling grain yield potential. Because wheat yield potential at higher temperatures decreased as [CO2] increased, a northly shift in the spring wheat growing areas may occur if global temperatures increased in concert with [CO2].