HR: 10:20h
AN: B12C-01    [Abstracts]
TI: Water isotopologues in leaves
AU: * Cuntz, M
EM: mcuntz@bgc-jena.mpg.de
AF: Max-Planck-Institut f\"ur Biogeochemie, Postfach 100164, Jena, 07701, Germany
AU: Ogée, J
EM: ogee@pierroton.inra.fr
AF: INRA, EPHYSE, BP 81, Villenave d'Ornon, 33883, France
AU: Farquhar, G D
EM: Graham.Farquhar@anu.edu.au
AF: Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, 2601, Australia
AU: Cernusak, L A
EM: CernusakL@si.edu
AF: Smithsonian Tropical Research Institute, Balboa, Ancón, 0000, Panama
AU: Peylin, P
EM: peylin@lsce.ipsl.fr
AF: BiOEMCO, CNRS/INRA/UPMC, Grignon, 78850, France
AU: Bariac, T
EM: bariac@grignon.inra.fr
AF: BiOEMCO, CNRS/INRA/UPMC, Grignon, 78850, France
AB: Leaf water isotope enrichment is a cornerstone of a variety of isotopic applications. It imprints on different substances such as atmospheric CO₂, O₂, and plant organic matter. But different applications use enrichment in different parts of the leaf and weighted by different fluxes. For example, leaf organic matter is determined by the assimilation-weighted average bulk water enrichment. Atmospheric CO₂ and O₂ are determined by the enrichment near the evaporating sites, either weighted by the one-way CO₂ flux from the stomata to the atmosphere or by electron transport, resp. These applications of leaf water enrichment are used from the leaf level up to global scales. It is therefore essential to understand the time course of leaf water enrichment at both the evaporating sites and in the mesophyll but also to asses the suitability of simple models such as the Craig & Gordon (1965) steady-state prediction or the Dongmann et al. (1974) non-steady-state model. We describe here advection and diffusion of water isotopologues in leaves in the non-steady state. We first show how this relates to earlier non-steady state bulk leaf water enrichment models. The adv.-diff. model compares very well with observations of bulk mesophyll water during the whole diel cycle. It compares well with the enrichment at the evaporative sites during the day but shows some deviations at night. It is clear that night-time stomatal conductance should be measured in the future. However, varying mesophyll water volume did not seem critical for a good prediction. In addition, observations of single diurnal cycles do not constrain the effective length in the mesophyll. Finally, we show when simpler models of leaf water enrichment are suitable for applications of leaf water isotopes once weighted with the appropriate gas exchange flux. We then present a two-dimensional adv.-diff. description of leaf water enrichment along monocot leaves. The model reproduces well all published measurements along monocot leaf blades, except at the leaf tip and giving the uncertainties on measurements and model parameters. Our results suggest that the observed differences between C₃ and C₄ plants reflect more mesophyll tortuosity rather than leaf length or interveinal distance. Using measurements of non-steady-state, spatially varying leaf water enrichment we show that spatial patterns are in steady state around midday only, just as observed for bulk leaf water, but can be easily up-scaled to the whole leaf level, independent of the degree of heterogeneity. This together suggests that regardless of the heterogeneity of leaf water enrichment, it is appropriate to take simple models of leaf water enrichment weighted with the appropriate gas exchange flux for applications involving leaf water isotope enrichment. References Cuntz M, Og\'ee J, Farquhar GD, Peylin P & Cernusak LA (2007) Modelling advection and diffusion of water isotopologues in leaves, Plant, Cell & Environment 30, 892-909 Farquhar GD & Cernusak LA (2005) On the isotopic composition of leaf water in the non-steady state, Functional Plant Biology 32, 293-303 Og\'ee J, Cuntz M, Peylin P & Bariac T (2007) Non-steady-state, non-uniform transpiration rate and leaf anatomy effects on the progressive stable isotope enrichment of leaf water along monocot leaves, Plant, Cell & Environment 30, 367-387
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0466 Modeling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting