title: Drought limitation of photosynthesis differs between C₃and C₄grass species in a comparative experiment.
abstract: Phylogenetic analyses show that C₄ grasses typically occupy drier habitats than their C₃ relatives, but recent experiments comparing the physiology of closely related C₃ and C₄ species have shown that advantages of C₄ photosynthesis can be lost under drought. We tested the generality of these paradoxical findings in grass species representing the known evolutionary diversity of C₄ NADP-me and C₃ photosynthetic types. Our experiment investigated the effects of drought on leaf photosynthesis, water potential, nitrogen, chlorophyll content and mortality. C₄ grasses in control treatments were characterized by higher CO₂ assimilation rates and water potential, but lower stomatal conductance and nitrogen content. Under drought, stomatal conductance declined more dramatically in C₃ than C₄ species, and photosynthetic water-use and nitrogen-use efficiency advantages held by C₄ species under control conditions were each diminished by 40%. Leaf mortality was slightly higher in C₄ than C₃ grasses, but leaf condition under drought otherwise showed no dependence on photosynthetic-type. This phylogenetically controlled experiment suggested that a drought-induced reduction in the photosynthetic performance advantages of C₄ NADP-me relative to C₃ grasses is a general phenomenon.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S102TN, UK.
authors.forename: S H
authors.initials: SH
authors.lastname: Taylor
authors.forename: B S
authors.initials: BS
authors.lastname: Ripley
authors.forename: F I
authors.initials: FI
authors.lastname: Woodward
authors.forename: C P
authors.initials: CP
authors.lastname: Osborne
mesh_terms: D000375:Aging; D044822:Biodiversity; D005075:Biological Evolution; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D055864:Droughts; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D010802:Phylogeny; D018515:Plant Leaves / Q000502:physiology*; D006109:Poaceae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011897:Random Allocation; D013045:Species Specificity; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D009584:Nitrogen