Carbon Dioxide Enrichment Effects Upon Yield and Yield Components in Wheat1

Two hard red spring wheat ( Triticum aestivum L.) genotypes, the commercial variety ‘Era’ and an experimental genotype ‘8037,’ selected for this work because it had unusually large heads, were grown in normal air and in atmospheres enriched in CO 2 to 600 ppm by volume in the field and in growth chambers in two day/night temperature regimes of 25/20 and 13/17 C. The growth period was divided into three stages: a) the vegetative period from germination to floral initiation; b) the floral development stage from floral initiation until anthesis; and c) the grain development stage from anthesis until maturity. Normal or CO 2 enriched air was applied during each of these developmental stages in all possible combinations giving eight treatments in each experiment. Both genotypes showed an increase in grain yield in the field and in the 25/20 C temperature regime in growth chambers when CO 2 enrichment was applied during stage b or c or both. No effect of CO 2 enrichment on grain yield was observed when the enrichment was applied before stage b in any experiment or at any development stage in the 13/17 C temperature regime. For both genotypes in the field and in the 25/20 temperature regime, CO 2 enrichment caused an increase in kernel number/plant when applied during stage b, and in kernel size when applied during stage c. This suggests that kernel number and size are both dependent on the supply of photosynthate. Thus, we conclude that a screening procedure, that is effective in classifying genotypes as to their photosynthetic capacity during either stages b or c, might be useful in identifying desirable parental lines for a yield‐oriented wheat breeding program.