Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements

Ying Sun, Lianhong Gu, Robert E. Dickinson, Stephen G. Pallardy, John Baker, Yonghui Cao, Fábio Murilo DaMatta, Xuejun Dong, David Ellsworth, Davina Van Goethem, Anna M. Jensen, Beverly E. Law, Rodolfo Loos, Samuel C. Vitor Martins, Richard J. Norby, Jeffrey Warren, David Weston, Klaus Winter

    Research output: Contribution to journalArticlepeer-review

    60 Citations (Scopus)

    Abstract

    Worldwide measurements of nearly 130 C3 species covering all major plant functional types are analysed in conjunction with model simulations to determine the effects of mesophyll conductance (gm) on photosynthetic parameters and their relationships estimated from A/Ci curves. We find that an assumption of infinite gm results in up to 75% underestimation for maximum carboxylation rate Vcmax, 60% for maximum electron transport rate Jmax, and 40% for triose phosphate utilization rate Tu. Vcmax is most sensitive, Jmax is less sensitive, and Tu has the least sensitivity to the variation of gm. Because of this asymmetrical effect of gm, the ratios of Jmax to Vcmax, Tu to Vcmax and Tu to Jmax are all overestimated. An infinite gm assumption also limits the freedom of variation of estimated parameters and artificially constrains parameter relationships to stronger shapes. These findings suggest the importance of quantifying gm for understanding in situ photosynthetic machinery functioning. We show that a nonzero resistance to CO2 movement in chloroplasts has small effects on estimated parameters. A non-linear function with gm as input is developed to convert the parameters estimated under an assumption of infinite gm to proper values. This function will facilitate gm representation in global carbon cycle models. Our previous understanding of the in situ operation of C3 photosynthetic machinery has been based on the invalid assumption of infinite mesophyll conductance. We show that this assumption significantly underestimates chloroplasts' photosynthetic potential and distorts relationships among fundamental photosynthetic parameters. A function is developed to convert photosynthetic parameters estimated under the invalid assumption to proper values. This function facilitates the representation of mesophyll conductance in carbon cycle models.
    Original languageEnglish
    Pages (from-to)978-994
    Number of pages17
    JournalPlant, Cell and Environment
    Volume37
    Issue number4
    DOIs
    Publication statusPublished - 2014

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