Patterns of plant macroevolution, maximum stomatal conductance and vein density.


Using modern plant trait relationships between observed and theoretical maximum stomatal conductance and vein density to examine patterns of plant macroevolution

by McElwain J. C. , Yiotis C., Lawson T. (2015)

Jennifer C. McElwain, University College Dublin, Belfield, Ireland, jennifer_mcelwain

Charilaos Yiotios, University College Dublin, Belfield, Ireland, charilaos_yiotis

Tracy Lawson, University of Essex, Colchester, UK, tracy_lawson

in New Phytologist 2016 Jan; 209(1): 94-103. doi: 10.1111/nph. –

Relationship between stomatal and photosynthetic traits. (a) Scaling relationship between maximum theoretical stomatal conductance (g max) and mean operational stomatal conductance (g op) of five gymnosperms (green squares), one fern (blue squares) and 12 angiosperm (pink squares) species measured using the ‘variance protocol’ in glasshouse conditions over a 5–13 d period in 2011–2012. All data points represent mean g op values of between 42 and 72 individual measurements per species regressed against g max (g op = 0.2507 g max; r 2 = 0.5446, P = 0.00039). (b) Species g op : g max scaling relationships (± standard deviation) regressed against mean saturated photosynthetic rate (A sat) (g op : g max = 0.0125A sat + 0.093; r 2 = 0.36652; P = 0.007758). Examples of species studied from left to right include Nageia nagi, Ginkgo biloba and Lepidozamia peroffskyana (upper panel) and Colocasia esculenta, Osmunda regalis and Ricinus communis (lower panel). –


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.


Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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