title: Using modern plant trait relationships between observed and theoretical maximum stomatal conductance and vein density to examine patterns of plant macroevolution.
abstract: Understanding the drivers of geological-scale patterns in plant macroevolution is limited by a hesitancy to use measurable traits of fossils to infer palaeoecophysiological function. Here, scaling relationships between morphological traits including maximum theoretical stomatal conductance (gmax ) and leaf vein density (Dv ) and physiological measurements including operational stomatal conductance (gop ), saturated (Asat ) and maximum (Amax ) assimilation rates were investigated for 18 extant taxa in order to improve understanding of angiosperm diversification in the Cretaceous. Our study demonstrated significant relationships between gop , gmax and Dv that together can be used to estimate gas exchange and the photosynthetic capacities of fossils. We showed that acquisition of high gmax in angiosperms conferred a competitive advantage over gymnosperms by increasing the dynamic range (plasticity) of their gas exchange and expanding their ecophysiological niche space. We suggest that species with a high gmax (> 1400 mmol m(-2) s(-1) ) would have been capable of maintaining a high Amax as the atmospheric CO2 declined through the Cretaceous, whereas gymnosperms with a low gmax would experience severe photosynthetic penalty. Expansion of the ecophysiological niche space in angiosperms, afforded by coordinated evolution of high gmax , Dv and increased plasticity in gop , adds further functional insights into the mechanisms driving angiosperm speciation.
authors.affiliation: Earth Institute, O'Brien Centre for Science, University College Dublin, Belfield, Ireland.|School of Biology and Environmental Science, University College Dublin, Belfield, Ireland.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: McElwain
authors.affiliation: Earth Institute, O'Brien Centre for Science, University College Dublin, Belfield, Ireland.|School of Biology and Environmental Science, University College Dublin, Belfield, Ireland.
authors.forename: Charilaos
authors.initials: C
authors.lastname: Yiotis
authors.affiliation: School of Biological Science, University of Essex, Colchester, CO4 3SQ, UK.
authors.forename: Tracy
authors.initials: T
authors.lastname: Lawson
mesh_terms: D005075:Biological Evolution; D032462:Cycadopsida / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology; D005580:Fossils; D019684:Magnoliopsida / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology; D054046:Plant Stomata / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology; D018526:Plant Transpiration
keywords: evolution of angiosperms; functional traits; maximum theoretical stomatal conductance (gmax); palaeophysiology; plasticity; stomatal density; stomatal evolution; vein density (Dv)