Evolution

Old-Fashioned Carbon Fixing

+ See all authors and affiliations

Science  28 Nov 2008:
Vol. 322, Issue 5906, pp. 1304
DOI: 10.1126/science.322.5906.1304d

The grass family has evolved several innovations that have made it one of the most widespread and speciose plant families. One of these innovations has been the origin of the C4 photosynthetic pathway, which fixes carbon to form carbohydrates at relatively high temperatures and relatively low CO2 (in comparison to the older C3 pathway) and which is believed to have arisen independently several times within the grass lineage.

Vicentini et al. have created a well-supported phylogenetic tree of the grasses and concluded that the C4 pathway originated after a major radiation in the grasses that split the family into two large groups. They calibrated their tree with six fossils and determined that the common ancestor of the grasses appeared approximately 94 million years ago (Ma) in the upper Cretaceous and that C4 photosynthesis originated approximately 32 Ma in the Oligocene during a period when atmospheric CO2 levels declined. Furthermore, the authors note that parallel incidents of C4 evolution and reversion to C3 pathways were clustered at times that may be related to changes in global environmental conditions and that correlated with changes in global CO2 levels. — LMZ

Global Change Biol. 14, 10.1111/j.1365-2486.2008.01688.x (2008).

Navigate This Article