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

Abstract

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 CO 2 concentration. This study was conducted to evaluate elevated CO 2 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 CO 2 concentrations, 550 (elevated) or 370 (ambient) μmol mol −1 and two water treatments in a Free‐Air CO 2 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 CO 2 and water treatments significantly influenced the grain‐filling processes. Under drought stress conditions, elevated CO 2 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 CO 2 was due to a faster rate of grain filling. Effects of elevated CO 2 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 CO 2 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.