Bundle Sheath Leakiness and Light Limitation during C₄ Leaf and Canopy CO₂ Uptake

• Published in: Plant physiology (Bethesda) 2008-12, Vol.148 (4), p.2144-2155
• Main Authors: Kromdijk, Johannes, Schepers, Hans E, Albanito, Fabrizio, Fitton, Nuala, Carroll, Faye, Jones, Michael B, Finnan, John, Lanigan, Gary J, Griffiths, Howard
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biomass; C4 photosynthesis; Carbon - metabolism; Carbon dioxide; Carbon Dioxide - metabolism; Carbon isotopes; Ecosystem; Ecosystems; Electron Transport - physiology; Fundamental and applied biological sciences. Psychology; Leaves; Light; Luminous intensity; Models, Theoretical; Photosynthesis; Photosynthesis - physiology; Plant physiology and development; Plants; Poaceae - growth & development; Poaceae - metabolism; Respiration; Vegetation canopies; Whole Plant and Ecophysiology
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.108.129890

Perennial species with the C₄ pathway hold promise for biomass-based energy sources. We have explored the extent that CO₂ uptake of such species may be limited by light in a temperate climate. One energetic cost of the C₄ pathway is the leakiness ({phi}) of bundle sheath tissues, whereby a variable proportion of the CO₂, concentrated in bundle sheath cells, retrodiffuses back to the mesophyll. In this study, we scale {phi} from leaf to canopy level of a Miscanthus crop (Miscanthus x giganteus hybrid) under field conditions and model the likely limitations to CO₂ fixation. At the leaf level, measurements of photosynthesis coupled to online carbon isotope discrimination showed that leaves within a 3.3-m canopy (leaf area index = 8.3) show a progressive increase in both carbon isotope discrimination and {phi} as light decreases. A similar increase was observed at the ecosystem scale when we used eddy covariance net ecosystem CO₂ fluxes, together with isotopic profiles, to partition photosynthetic and respiratory isotopic flux densities (isofluxes) and derive canopy carbon isotope discrimination as an integrated proxy for {phi} at the canopy level. Modeled values of canopy CO₂ fixation using leaf-level measurements of {phi} suggest that around 32% of potential photosynthetic carbon gain is lost due to light limitation, whereas using {phi} determined independently from isofluxes at the canopy level the reduction in canopy CO₂ uptake is estimated at 14%. Based on these results, we identify {phi} as an important limitation to CO₂ uptake of crops with the C₄ pathway.