TEMPERATURE, NITROGEN, AND CARBON-DIOXIDE EFFECTS ON SPRING WHEAT DEVELOPMENT AND SPIKELET NUMBERS

Spring wheat (Triticum aestivum L.) responds favorably to elevated atm ospheric carbon dioxide concentration ([CO2]) at optimum temperatures. Predictions are for air temperatures to increase as global [CO2] incr eases. Since spring wheat grain yields generally decline as temperatur e increases, there is a need to understand the effects of both [CO2] a nd temperature on spring wheat growth, development, and yield potentia l. 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 whea t. '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 ai r temperatures. Temperature affected the Haun stage by growth degree-d ays (GDD) relationship more than N or [CO2]. The phyllochron in GDD wa s 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, b ut at 22/26 degrees C, spikelets increased as N increased and decrease d 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] an d adequate soil water, air temperature is more important than [CO2] in controlling grain yield potential. Because wheat yield potential at h igher temperatures decreased as [CO2] increased, a northly shift in th e spring wheat growing areas may occur if global temperatures increase d in concert with [CO2].