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C4 photosynthesis evolved in warm climates but promoted migration to cooler ones

Watcharamongkol, Teera, Christin, Pascal‐Antoine, Osborne, Colin P.
Ecology letters 2018 v.21 no.3 pp. 376-383
C3 plants, C4 photosynthesis, C4 plants, data collection, geographical distribution, grasses, phylogeny, temperate zones, temperature, tropics
C₄ photosynthesis is considered an adaptation to warm climates, where its functional benefits are greatest and C₄ plants achieve their highest diversity and dominance. However, whether inherent physiological barriers impede the persistence of C₄ species in cool environments remains debated. Here, we use large grass phylogenetic and geographical distribution data sets to test whether (1) temperature influences the rate of C₄ origins, (2) photosynthetic types affect the rate of migration among climatic zones, and (3) C₄ evolution changes the breadth of the temperature niche. Our analyses show that C₄ photosynthesis in grasses originated in tropical climates, and that C₃ grasses were more likely to colonise cold climates. However, migration rates among tropical and temperate climates were higher in C₄ grasses. Therefore, while the origins of C₄ photosynthesis were concentrated in tropical climates, its physiological benefits across a broad temperature range expanded the niche into warmer climates and enabled diversification into cooler environments.