Does a freely tillering wheat cultivar benefit more from elevated CO2 than a restricted tillering cultivar in a water-limited environment?

This study addresses whether a freely tillering wheat cultivar with greater vegetative sink strength (cv. "Silverstar") can benefit more from increasing atmospheric CO₂ concentration [CO₂] than a restricted tillering cultivar with greater reproductive sink strength (cv. H45) in a water-limited cropping system. Growth, yield, yield components and nitrogen at three developmental stages (stem elongation, anthesis, maturity) and water soluble carbohydrates (WSC, anthesis) were evaluated at two CO₂ concentrations (ambient [CO₂], ~395ppm, elevated e[CO₂], ~550ppm) across six environments using the Australian Grains Free Air CO₂ Enrichment (AGFACE) facility. Cv. "Silverstar" had more tillers than cv. "H45" throughout development; whereas, cv. "H45" had greater WSC storage and more and heavier kernels per spike. CO₂ enrichment stimulated grain yield in both cultivars similarly, but this stimulation was caused differently: For cv. "Silverstar", grain yield increase was exclusively linked to an increased number of fertile tillers; whereas, in cv. "H45", yield stimulation was additionally associated with increased kernel weight and kernel numbers per spike. We conclude that in a Mediterranean-type, water-limited environment high tillering capacity alone does not ensure greater benefits from CO₂ fertilization but that both pre and post-anthesis source-sink relationships play a significant role in this environment as well.