Edwards, Erika .
C4 the straw man? Evolution of cold tolerance better explains global distribution of C3/C4 grasslands.
C4 photosynthesis refers to a suite of traits that increase photosynthetic efficiency in high temperature environments. Most C4 plants are grasses (Poaceae), which account for ~25% of terrestrial primary production. C4 grasses are largely restricted to tropical and subtropical grasslands, and are replaced by C3 grasses in cooler climates. Enhanced C4 performance at high temperatures has been invoked to explain this C3/C4 temperature sorting. This has been a working premise of grassland biologists for 30+ years. However, it is possible that C4 grasses are simply adapted to warm conditions due to other traits they inherited from their non-C4 ancestors, as C4 origins are clustered in primarily tropical clades. I collated data from two public archives (NCBI and GBIF) to construct the largest possible grass phylogeny with quantitative climate data for all species. The final analysis included ~ 1,000 taxa represented by over 1.5 million geo-referenced specimens. Ancestral niche reconstructions suggest that Poaceae is essentially a warm climate clade; independent contrast analyses indicate that C4 evolution was not associated with shifts to warmer environments. However, all C4 origins were correlated with dramatic reductions in precipitation, suggesting that the C4 pathway played a fundamental role in the evolution of drought tolerance. Surprisingly, grasses have rarely invaded colder regions. Physiological innovations associated with cold tolerance may be more important than the C4 pathway in establishing patterns of species turnover along temperature gradients. As an aside, this study also illustrates how using standard functional type categories (i.e. C3/C4) can mask the true functional diversity that drives global ecological patterns.
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1 - Brown University, Department of Ecology and Evolutionary Biology, Box G, Providence, RI, 02912, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Alpine B/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 9:30 AM