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CROP PHYSIOLOGY & METABOLISM

Free-Air CO₂ Enrichment and Drought Stress Effects on Grain Filling Rate and Duration in Spring Wheat

^a NEI/NIH, Bld. 6 Rm 304, 6 Center Dr., Bethesda, MD 20892-2740 USA
^b Weed Science Lab., USDA-ARS, Washington State Univ., Pullman, WA 99164 USA
^c Jr., Water Conservation Lab., USDA-ARS, 4331 E. Broadway Rd., Phoenix, AZ 85040 USA
^d Associate Professor of Plant Sciences, Univ. of Idaho, Idaho Agric. Exp. Stn. Res. Paper No. 97735. Dep. of Plant, Soil and Entomological Sciences, Univ. of Idaho, Moscow, ID 83844-2339 USA

lia{at}intra.nei.nih.gov

Wheat grain weight is a function of rate and duration of grain growth and is affected by photosynthate supply. Drought stress reduces photosynthate production because of stomatal closure. However, this might be partially overcome by an increase in air CO₂ concentration. This study was conducted to evaluate elevated CO₂ and drought stress effects on grain-filling rate and duration for spring wheat (Triticum aestivum L.). Spring wheat (cv. Yecora Roja) was grown at two CO₂ concentrations, 550 (elevated) or 370 (ambient) µmol mol^-1 and two water treatments in a Free-Air CO₂ Enrichment (FACE) system at the University of Arizona Maricopa Agricultural Center. Plant samples were collected every 3 to 4 d from 6 d after anthesis until plant maturity. Main stem spikes were separated into upper, middle, and lower sections. Grain weight data for the intact main stem spike, each of its sections, and intact tiller spikes were fitted to a cumulative logistic model. Both elevated CO₂ and water treatments significantly influenced the grain-filling processes. Under drought stress conditions, elevated CO₂ increased grain weight in the upper and lower sections of the main stem spike by 10 and 24%, respectively. In well-watered plants, final grain weight in the midsection of the main stem spike was 8% higher than that measured under drought stress conditions. Grain weight increase under elevated CO₂ was due to a faster rate of grain filling. Effects of elevated CO₂ on the statistically derived duration of grain filling were inconclusive because of the confounding effect of blower-induced temperature changes on the process. An increase in grain weight of well-watered plants was due to a longer grain-filling period. Later-formed tiller spikes were more responsive to elevated CO₂ and drought stress than main stem spikes. Information from this study will help us understand the grain growth of wheat and provide information to establish grain growth mechanism.

Abbreviations: ATU, accumulated thermal units • FACE, free-air CO₂ enrichment • T1, T2, and T3, primary tillers

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