C3and C4photosynthesis inCyperus(Cyperaceae) in temperate eastern North America

Abstract

All species in the genus Cyperus (Cyperaceae) that occur in temperate eastern North America were assigned to either the C3or C4photosynthetic pathway using leaf anatomical characteristics and stable carbon isotope ratios. Of the 39 species in the study area, 32 had C4photosynthesis while 7 had C3. The numbers of C3, C4, and total Cyperus species were significantly and positively correlated with both summer precipitation and mean annual temperature. However, the proportional abundance of C4species within Cyperus was not significantly related to either climatic variable. The highest Cyperus diversity was found on the Atlantic Coastal Plain, a pattern that remained after climatic differences between regions were accounted for. All the C3species and the majority of the C4species were restricted to wetlands or damp soil habitats; 13 of the 32 C4species occurred in dry, sandy habitats. Given that the C3pathway is ancestral in the genus Cyperus, it appears that C4photosynthesis evolved in a wetland context for this genus. We suggest that the high nitrogen use efficiency associated with the C4pathway is largely responsible for the evolution and ecological success of C4Cyperus species in infertile, temperate wetlands.Key words: C3and C4photosynthetic pathways, Cyperus, Cyperaceae, eastern North America, stable carbon isotopes.