Phylogenetic niche conservatism in C4 grasses
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Photosynthetic pathway is used widely to discriminate plant functional types in studies of global change. However, independent evolutionary lineages of C4 grasses with different variants of C4 photosynthesis show different biogeographical relationships with mean annual precipitation, suggesting phylogenetic niche conservatism (PNC). To investigate how phylogeny and photosynthetic type differentiate C4 grasses, we compiled a dataset of morphological and habitat information of 185 genera belonging to two monophyletic subfamilies, Chloridoideae and Panicoideae, which together account for 90 % of the world’s C4 grass species. We evaluated evolutionary variance and covariance of morphological and habitat traits. Strong phylogenetic signals were found in both morphological and habitat traits, arising mainly from the divergence of the two subfamilies. Genera in Chloridoideae had significantly smaller culm heights, leaf widths, 1,000-seed weights and stomata; they also appeared more in dry, open or saline habitats than those of Panicoideae. Controlling for phylogenetic structure showed significant covariation among morphological traits, supporting the hypothesis of phylogenetically independent scaling effects. However, associations between morphological and habitat traits showed limited phylogenetic covariance. Subfamily was a better explanation than photosynthetic type for the variance in most morphological traits. Morphology, habitat water availability, shading, and productivity are therefore all involved in the PNC of C4 grass lineages. This study emphasized the importance of phylogenetic history in the ecology and biogeography of C4 grasses, suggesting that divergent lineages need to be considered to fully understand the impacts of global change on plant distributions.
KeywordsPhylogenetic niche conservatism C3/C4 photosynthesis Poaceae Morphology Habitat
We gratefully thank Samuel Taylor for discussion on statistics. This work was funded by a UK/China Excellence Scholarship from the China Scholarship Council and the UK Government Department for Innovation, Universities and Skills (now Department for Business, Innovation and Skills).
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