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Response of wild C 4 crop progenitors to subambient CO 2 highlights a possible role in the origin of agriculture
Author(s) -
CUNNIFF JENNIFER,
OSBORNE COLIN P.,
RIPLEY BRAD S.,
CHARLES MICHAEL,
JONES GLYNIS
Publication year - 2008
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2007.01515.x
Subject(s) - glacial period , transpiration , photosynthesis , domestication , stomatal conductance , biomass (ecology) , crop , deglaciation , water use efficiency , productivity , climate change , last glacial maximum , carbon dioxide , environmental science , agronomy , biology , physical geography , botany , horticulture , ecology , geography , paleontology , macroeconomics , economics
The synchronous origin of agriculture in at least four independent climatic regions at the end of the last glacial period (c10 kyr bp ) points to a global limitation for crop domestication. One hypothesis proposes that a rapid carbon dioxide (CO 2 ) increase from 18 Pa to ∼27 Pa during deglaciation caused significant increases in the growth rates of wild crop progenitors, thereby removing a productivity barrier to their successful domestication. However, early C 4 crops present a challenge to this hypothesis, because they were among the first domesticates, but have a carbon‐concentrating mechanism that offsets the limitation of photosynthesis by CO 2 . We investigated the CO 2 ‐limitation hypothesis using the wild progenitors of five C 4 founder crops from four independent centres of domestication. Plants were grown in controlled environment chambers at glacial (18 Pa), postglacial (28 Pa) and current ambient (38 Pa) CO 2 levels, and photosynthesis, transpiration and biomass were measured. An increase in CO 2 from glacial to postglacial levels caused a significant gain in vegetative biomass of up to 40%, but the equivalent rise in CO 2 from postglacial to modern levels generally had no effect on biomass. Investigation into the underlying mechanisms showed C 4 photosynthesis to be limited more by glacial than postglacial CO 2 levels, matching theoretical expectations. Moreover, the increase in CO 2 from glacial to postglacial levels caused a reduction in the transpiration rate via decreases in stomatal conductance of ∼35%. In combination, these physiological changes conferred a large improvement in water‐use efficiency at the postglacial CO 2 partial pressure compared with the glacial level. Our data, therefore, provide experimental support for the CO 2 ‐limitation hypothesis, suggesting that these key physiological changes could have greatly enhanced the productivity of wild crop progenitors after deglaciation.