title: Yield responses of wild C3and C4crop progenitors to subambient CO2: a test for the role of CO2limitation in the origin of agriculture.
abstract: Limitation of plant productivity by the low partial pressure of atmospheric CO2(Ca) experienced during the last glacial period is hypothesized to have been an important constraint on the origins of agriculture. In support of this hypothesis, previous work has shown that glacial Calimits vegetative growth in the wild progenitors of both C3and C4founder crops. Here, we present data showing that glacial Caalso reduces grain yield in both crop types. We grew four wild progenitors of C3(einkorn wheat and barley) and C4crops (foxtail and broomcorn millets) at glacial and postglacial Ca, measuring grain yield and the morphological and physiological components contributing to these yield changes. The C3species showed a significant increase in unthreshed grain yield of ~50% with the glacial to postglacial increase in Ca, which matched the stimulation of photosynthesis, suggesting that increases in photosynthesis are directly translated into yield at subambient levels of Ca. Increased yield was controlled by a higher rate of tillering, leading to a larger number of tillers bearing fertile spikes, and increases in seed number and size. The C4species showed smaller, but significant, increases in grain yield of 10-15%, arising from larger seed numbers and sizes. Photosynthesis was enhanced by Cain only one C4species and the effect diminished during development, suggesting that an indirect mechanism mediated by plant water relations could also be playing a role in the yield increase. Interestingly, the C4species at glacial Cashowed some evidence that photosynthetic capacity was upregulated to enhance carbon capture. Development under glacial Caalso impacted negatively on the subsequent germination and viability of seeds. These results suggest that the grain production of both C3and C4crop progenitors was limited by the atmospheric conditions of the last glacial period, with important implications for the origins of agriculture.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Cunniff
authors.affiliation: Department of Archaeology, Northgate House, University of Sheffield, West Street, Sheffield, S1 4ET, UK.
authors.forename: Glynis
authors.initials: G
authors.lastname: Jones
authors.affiliation: School of Archaeology, University of Oxford, 34-36 Beaumont Street, Oxford, OX1 2PG, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Charles
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Colin P
authors.initials: CP
authors.lastname: Osborne
mesh_terms: D000383:Agriculture; D002245:Carbon Dioxide; D010788:Photosynthesis; D006109:Poaceae; D014908:Triticum / Q000254:growth & development*
chemical_list: D002245:Carbon Dioxide
keywords: crop progenitor; germination; origin of agriculture; photosynthesis; stomatal conductance; subambient CO2; viability; yield