title: Coupled response of stomatal and mesophyll conductance to light enhances photosynthesis of shade leaves under sunflecks.
abstract: Light gradients within tree canopies play a major role in the distribution of plant resources that define the photosynthetic capacity of sun and shade leaves. However, the biochemical and diffusional constraints on gas exchange in sun and shade leaves in response to light remain poorly quantified, but critical for predicting canopy carbon and water exchange. To investigate the CO2diffusion pathway of sun and shade leaves, leaf gas exchange was coupled with concurrent measurements of carbon isotope discrimination to measure net leaf photosynthesis (An), stomatal conductance (gs) and mesophyll conductance (gm) in Eucalyptus tereticornis trees grown in climate controlled whole-tree chambers. Compared to sun leaves, shade leaves had lower An, gm, leaf nitrogen and photosynthetic capacity (Amax) but gswas similar. When light intensity was temporarily increased for shade leaves to match that of sun leaves, both gsand gmincreased, and Anincreased to values greater than sun leaves. We show that dynamic physiological responses of shade leaves to altered light environments have implications for up-scaling leaf level measurements and predicting whole canopy carbon gain. Despite exhibiting reduced photosynthetic capacity, the rapid up-regulation of gmwith increased light enables shade leaves to respond quickly to sunflecks.
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, 2751, NSW, Australia.
authors.forename: Courtney E
authors.initials: CE
authors.lastname: Campany
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, 2751, NSW, Australia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Tjoelker
authors.affiliation: ARC Centre of Excellence for Translational Photosynthesis, Plant Science Division, Research School of Biology, The Australian National University, Canberra, 2601, ACT, Australia.
authors.forename: Susanne
authors.initials: S
authors.lastname: von Caemmerer
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, 2751, NSW, Australia.
authors.forename: Remko A
authors.identifier: 0000-0002-8499-5580
authors.initials: RA
authors.lastname: Duursma
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D005052:Eucalyptus / Q000378:metabolism; D008027:Light; D058503:Mesophyll Cells / Q000528:radiation effects*; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism*; D054046:Plant Stomata / Q000528:radiation effects*; D013472:Sunlight
chemical_list: D002245:Carbon Dioxide
keywords: Eucalyptus tereticornis; canopy light gradients; climate warming; leaf nitrogen; shade acclimation