Assessing the impact of internal conductance to CO2 in a land-surface scheme: measurement and modelling of photosynthesis in Populus nigra

Oliver, Rebecca J.; Taylor, Gail; Finch, Jon W.. 2012 Assessing the impact of internal conductance to CO2 in a land-surface scheme: measurement and modelling of photosynthesis in Populus nigra. Agricultural and Forest Meteorology, 152. 240-251.

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Vegetation plays a key role in both the global carbon and water cycles. Therefore, the representation of leaf-level fluxes of carbon and water in process-based land-surface schemes is central to accurately predicting these surface exchanges on a larger scale. Leaf-level models of photosynthesis used in such schemes are commonly based on the equations of Farquhar et al. (1980), which were founded on the assumption that differences in the drawdown of CO2 from sub-stomatal cavities (ci) to the site of carboxylation inside chloroplasts (cc) were negligible. Recent research, however, indicates an important role for this additional internal pathway of CO2 transfer (gi) in photosynthesis. This work therefore combined fieldwork and modelling to assess the impact of gi on estimation of key photosynthetic parameters, and on the accuracy of simulated photosynthesis (Anet) and stomatal conductance (gs) in a coupled model of leaf-level Anet and gs embedded in a land-surface scheme. It was shown that, in a fast growing poplar genotype (Populus nigra), the photosynthetic parameter Vmax was sensitive to gi. Determination of Vmax under the assumption of finite gi led to estimates of Vmax in well-watered trees that were, on average, 52% higher than values calculated on a ci basis. Drought induced declines in all key photosynthetic parameters measured were observed (Vmax, Jmax and gi), in addition to a two-fold increase in photosynthetic biochemical capacity upon re-watering. Reasons for this and the implications for land-surface modelling are discussed. It was shown that inclusion of a constant (non-water stressed) internal conductance to CO2 in a coupled model of leaf-level Anet and gs did not improve the accuracy of these simulated fluxes. It was concluded that, for application within a land-surface scheme, currently, accurate calibration of Vmax potentially has a greater impact on simulated Anet and gs than the inclusion of additional, fine-scale leaf-level processes such as gi.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Water > WA Topic 2 - Ecohydrological Processes > WA - 2.2 - Integrate the effect of urban and rural land use on the ecohydrological functioning of a landscape mosaic
UKCEH and CEH Sections/Science Areas: Reynard
ISSN: 0168-1923
Additional Information. Not used in RCUK Gateway to Research.: The attached document is the author’s version of a work that was accepted for publication in Agricultural and Forest Meteorology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Agricultural and Forest Meteorology, 152. 240-251. 10.1016/j.agrformet.2011.10.001
Additional Keywords: land-surface model, poplar, gas exchange, Vmax, mesophyll conductance
NORA Subject Terms: Hydrology
Date made live: 07 Nov 2011 14:45 +0 (UTC)

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