title: Effect of local irradiance on CO(2) transfer conductance of mesophyll in walnut.
abstract: The acclimation responses of walnut leaf photosynthesis to the irradiance microclimate were investigated by characterizing the photosynthetic properties of the leaves sampled on young trees (Juglans nigraxregia) grown in simulated sun and shade environments, and within a mature walnut tree crown (Juglans regia) in the field. In the young trees, the CO(2) compensation point in the absence of mitochondrial respiration (Gamma*), which probes the CO(2) versus O(2) specificity of Rubisco, was not significantly different in sun and shade leaves. The maximal net assimilation rates and stomatal and mesophyll conductances to CO(2) transfer were markedly lower in shade than in sun leaves. Dark respiration rates were also lower in shade leaves. However, the percentage inhibition of respiration by light during photosynthesis was similar in both sun and shade leaves. The extent of the changes in photosynthetic capacity and mesophyll conductance between sun and shade leaves under simulated conditions was similar to that observed between sun and shade leaves collected within the mature tree crown. Moreover, mesophyll conductance was strongly correlated with maximal net assimilation and the relationships were not significantly different between the two experiments, despite marked differences in leaf anatomy. These results suggest that photosynthetic capacity is a valuable parameter for modelling within-canopies variations of mesophyll conductance due to leaf acclimation to light.
authors.affiliation: Laboratoire d'Ecophysiologie Végétale, UPRESA 8079 CNRS-Université Paris Sud, F-91405 Orsay, France.
authors.forename: Clément
authors.initials: C
authors.lastname: Piel
authors.forename: Ela
authors.initials: E
authors.lastname: Frak
authors.forename: Xavier
authors.initials: X
authors.lastname: Le Roux
authors.forename: Bernard
authors.initials: B
authors.lastname: Genty
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D031324:Juglans / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects*; D010788:Photosynthesis; D013050:Spectrometry, Fluorescence
chemical_list: D002245:Carbon Dioxide