Effects of elevated atmospheric CO2 and drought stress on individual grainfilling rates and durations of the main stem in spring wheat

Rate and duration of individual grain growth determine final kernel weight and are influenced by environmental factors. The objectives of this researc h were to assess the effects of elevated CO2 and drought stress on the grai n filling rate and duration, and the weight of individual kernels. Spring w heat (Triticum aestivum L.) was grown in a free air CO2 enrichment (FACE) s ystem on the demonstration farm at the University of Arizona Maricopa Agric ultural Center with a split-block design of four replications. Mainplots we re 550 or 370 mu mol mol(-1) of atmospheric CO2 concentrations and subplots were two irrigation treatments. The weights of individual kernels from upp er. middle, and lower spikelets of the main stem spike were fitted into non linear cumulative logistic curves as a function of accumulated thermal unit s using SAS proc NLIN. Rate and duration of individual grain filling varied greatly depending on floret positions and environmental factors. The combi nation of these changes determined the final weight of individual kernels. The rank order of kernel weights among kernel positions within a middle and lower spikelet was not affected by either elevated CO2 or water stress tre atments in this study. Elevated CO2 often stimulated the rate of individual grain filling, whereas the well-watered condition extended duration of ind ividual grain filling. Furthermore, kernels further from the rachis or near est to the rachis were affected proportionately more than those towards the center of a spikelet. The information from this research will be used to m odel wheat grain growth as a function of climate. (C) 2001 Elsevier Science B.V. All rights reserved.