Free-air CO2 enrichment and drought stress effects on grain filling rate and duration in spring wheat

Wheat grain weight is a function of rate and duration of grain growth and i s affected by photosynthate supply. Drought stress reduces photosynthate pr oduction because of stomatal closure. However, this might be partially over come by an increase in air CO2 concentration. This study was conducted to e valuate elevated CO2 and drought stress effects on grain-filling rate and d uration for spring wheat (Triticum aestivum L.), Spring wheat (cv. Yecora R oja) was grown at two CO2 concentrations, 550 (elevated) or 370 (ambient) p mol mol(-1) and two water treatments in a Free-Air CO2 Enrichment (FACE) sy stem at the University of Arizona Maricopa Agricultural Center. Plant sampl es were collected every 3 to 4 d from 6 d after anthesis until plant maturi ty. Main stem spikes were separated into upper, middle, and lower sections. Grain weight data for the intact main stem spike, each of its sections, an d intact tiller spikes were fitted to a cumulative logistic model. Both ele vated CO2 and water treatments significantly influenced the grain-filling p rocesses. Under drought stress conditions, elevated CO2 increased grain wei ght in the upper and lower sections of the main stem spike by 10 and 24%, r espectively. In well-watered plants, final grain weight in the midsection o f 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 r ate of grain filling. Effects of elevated CO2 on the statistically derived duration of grain tilling were inconclusive because of the confounding effe ct of blower-induced temperature changes on the process. An increase in gra in weight of well-watered plants was due to a longer grain-tilling 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 und erstand the grain growth of wheat and provide information to establish grai n growth mechanism.