Consistent allometric scaling of stomatal sizes and densities across taxonomic ranks and geologic time

H.J. de Boer, C.A. Price, F. Wagner-Cremer, S.C. Dekker, E.J. Veneklaas

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Abstract

Stomatal pores on plants leaves are an important link in the chain of processes that determine biosphere fluxes of water and carbon. Stomatal density (i.e. the number of stomata per area) and the size of the stomatal pore at maximum aperture are particularly relevant traits in this context because they determine the theoretical maximum diffusive stomatal conductance (gsmax) and thereby set an upper limit for leaf gas exchange. Observations on (sub)fossil leaves revealed that changes in stomatal densities are anti-correlated with changes in stomatal sizes at developmental and evolutionary timescales. Moreover, this anti-correlation appears consistently within single species, across multiple species in the extant plant community and at evolutionary time scales. The consistency of the relation between stomatal densities and sizes suggests that common mechanisms constrain the adaptation of these traits across the plant community. In an attempt to identify such potential generic constraints, we investigated the allometry between stomatal densities and sizes in the extant plant community and across geological time. As the size of the stomatal pore at maximum aperture is typically derived from the length of the stomatal pore, we considered the allometric scaling of pore length (lp) with stomatal density (Ds) as the power law: lp = k . Dsa in which k is a normalization constant and the exponent a is the slope of the scaling relation. Our null-hypothesis predicts that stomatal density and pore length scale along a constant slope of -1/2 based on a scale-invariant relation between pore length and the distance between neighboring pores. Our alternative hypothesis predicts a constant slope of -1 based on the idea that stomatal density and pore length scale along an invariant gsmax. To explore these scaling hypotheses in the extant plant community we compiled a dataset of combined observations of stomatal density and pore length on 111 species from published literature and new measurements. These data encompass a wide range of environmental conditions, including the CO2 rise of the last century. Using a bootstrapping resampling strategy we found consistent allometric scaling of stomatal density and pore length with slopes between -1/2 and -1 at different taxonomic ranks in the extant plant community (i.e. across all species, within the angiosperm and gymnosperm clades, within specific families, and within individual species), despite large differences in climate and atmospheric CO2 concentrations. Similar allometric scaling was found in evolutionary adaptations of these traits across geological time. These results suggest that the observed ranges of stomatal densities and sizes are constrained by their diffusive properties in addition to scale-invariant spatial interactions. Moreover, the similarity in the scaling of these traits throughout the extant plant community and across geological time could aid the development of an integrative framework to predict developmental and evolutionary adaptations of stomatal traits under climate change.
Original languageEnglish
PagesH12D-08
Publication statusPublished - 7 Dec 2013
EventAGU Fall meeting 2013, oral Session (invited speaker) - San Fransisco, USA
Duration: 1 Jan 2013 → …

Conference

ConferenceAGU Fall meeting 2013, oral Session (invited speaker)
CitySan Fransisco, USA
Period1/01/13 → …

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