Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2008
Publication Date: 3/1/2008
Citation: Ziska, L.H. 2008. Three year field evaluation of early and late 20th century spring wheat cultivars to projected increases in atmospheric carbon dioxide. Field Crops Research. 108:54-59.
Interpretive Summary: Carbon dioxide (CO2), along with sunlight, water, and nutrients constitutes one of the four resources needed for plants to grow. As such, the sudden increase in its concentration in the atmosphere (up 22% since 1960) could be exploited in order to boost crop yields. Wheat is a principal source of calories for 10-15% of the global population. Here we evaluate for the first time, whether modern lines of wheat show the same sensitivity to rising carbon dioxide as older, pre green revolution lines. The two wheat lines evaluated were "Oxen" a modern line, and "Marquis" a pre green revolution line. Our results tell us that newer lines are not more responsive to rising CO2 levels; rather, that the ability of each wheat line to respond to CO2 may be dependent on how the plant utilizes the additional carbon. Overall, understanding and characterizing how different wheat lines respond to rising carbon dioxide may offer new opportunities for breeders to exploit and adapt lines of wheat to projected increases in atmospheric carbon dioxide concentration. This data and its inference for food security will be of interest for policy makers, scientists, agronomists, and plant breeders.
Technical Abstract: Carbon dioxide (CO2), along with light, water and nutrients represents an essential resource needed for plant growth and reproduction. Recent and projected increases in atmospheric carbon dioxide may allow breeders and agronomists to begin intra-specific selection for CO2 sensitivity to these traits. However, selection for optimal yield, particularly for cereals, is ongoing, and it is possible that modern cereal lines are, in fact, the most CO2 sensitive lines available. To test CO2 responsiveness, we examined two contrasting spring wheat lines, Marquis and Oxen, over a three year period under field conditions at two different planting densities. Marquis was introduced into North America in 1903, and is taller, with greater tiller plasticity, smaller seed and lower harvest index relative to modern wheat lines. Oxen, a modern wheat line released in 1996, produces fewer tillers, and has larger seed with a higher harvest index relative to Marquis. As would be expected, under ambient CO2 conditions, Oxen produced more seed than Marquis for all three years. However, at a CO2 concentration 250 µmol mol-1 above ambient, (a concentration anticipated in the next 50-100 years), no differences were observed in seed yield between the two cultivars, and vegetative biomass (tillers,) was significantly higher for Marquis relative to Oxen in 2006 and 2007. Significant CO2 by cultivar interaction was observed as a result of relatively greater tiller production and an increased percentage of tillers bearing panicles for the Marquis relative to the Oxen cultivar at elevated carbon dioxide. This greater increase in tiller bearing panicles also resulted in a significant increase in harvest index for the Marquis cultivar as CO2 increased. While preliminary, these results intimate that newer lines are not intrinsically more CO2 responsive; rather, that yield sensitivity may be dependent on the availability of reproductive sinks to assimilate additional carbon. Overall, understanding and characterizing vegetative vs. reproductive sink capacity between cultivars may offer new opportunities for breeders to exploit and adapt lines of wheat to projected increases in atmospheric carbon dioxide concentration.