title: Genetic variation in circadian regulation of nocturnal stomatal conductance enhances carbon assimilation and growth.
abstract: Circadian resonance, whereby a plant's endogenous rhythms are tuned to match environmental cues, has been repeatedly shown to be adaptive, although the underlying mechanisms remain elusive. Concomitantly, the adaptive value of nocturnal transpiration in C3 plants remains unknown because it occurs without carbon assimilation. These seemingly unrelated processes are interconnected because circadian regulation drives temporal patterns in nocturnal stomatal conductance, with maximum values occurring immediately before dawn for many species. We grew individuals of six Eucalyptus camaldulensis genotypes in naturally lit glasshouses and measured sunset, predawn and midday leaf gas exchange and whole-plant biomass production. We tested whether sunrise anticipation by the circadian clock and subsequent increases in genotype predawn stomatal conductance led to rapid stomatal opening upon illumination, ultimately affecting genotype differences in carbon assimilation and growth. We observed faster stomatal responses to light inputs at sunrise in genotypes with higher predawn stomatal conductance. Moreover, early morning and midday stomatal conductance and carbon assimilation, leaf area and total plant biomass were all positively correlated with predawn stomatal conductance across genotypes. Our results lead to the novel hypothesis that genotypic variation in the circadian-regulated capacity to anticipate sunrise could be an important factor underlying intraspecific variation in tree growth.
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, 2753, Australia.|Department of Crop and Forest Sciences - AGROTECNIO Center, Universitat de Lleida, 25198, Lleida, Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Resco de Dios
authors.affiliation: Department of Environmental Studies, University of California, Santa Cruz, CA, 95064, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Loik
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, 2753, Australia.
authors.forename: Renee
authors.initials: R
authors.lastname: Smith
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, 2753, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Aspinwall
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, 2753, Australia.
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
mesh_terms: D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D057906:Circadian Clocks; D005052:Eucalyptus / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects; D014644:Genetic Variation; D005838:Genotype; D008027:Light; D008954:Models, Biological; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D054046:Plant Stomata / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration; D014197:Trees
chemical_list: D002245:Carbon Dioxide; D002244:Carbon
keywords: CO2; adaptation; anticipation hypothesis; biomass enhancement; circadian clock; gas exchange; genotype; memory; nocturnal transpiration; stomata