Mesophyll conductance in land surface models: effects on photosynthesis and transpiration

Jürgen Knauer*, Sönke Zaehle, Martin G. De Kauwe, Vanessa Haverd, Markus Reichstein, Ying Sun

*Corresponding author for this work

Research output: Contribution to journalReview article (Academic Journal)peer-review

14 Citations (Scopus)

Abstract

The CO2 transfer conductance within plant leaves (mesophyll conductance, gm) is currently not considered explicitly in most land surface models (LSMs), but instead treated implicitly as an intrinsic property of the photosynthetic machinery. Here, we review approaches to overcome this model deficiency by explicitly accounting for gm, which comprises the re-adjustment of photosynthetic parameters and a model describing the variation of gm in dependence of environmental conditions. An explicit representation of gm causes changes in the response of photosynthesis to environmental factors, foremost leaf temperature, and ambient CO2 concentration, which are most pronounced when gm is small. These changes in leaf-level photosynthesis translate into a stronger climate and CO2 response of gross primary productivity (GPP) and transpiration at the global scale. The results from two independent studies show consistent latitudinal patterns of these effects with biggest differences in GPP in the boreal zone (up to ~15%). Transpiration and evapotranspiration show spatially similar, but attenuated, changes compared with GPP. These changes are indirect effects of gm caused by the assumed strong coupling between stomatal conductance and photosynthesis in current LSMs. Key uncertainties in these simulations are the variation of gm with light and the robustness of its temperature response across plant types and growth conditions. Future research activities focusing on the response of gm to environmental factors and its relation to other plant traits have the potential to improve the representation of photosynthesis in LSMs and to better understand its present and future role in the Earth system.

Original languageEnglish
Pages (from-to)858-873
Number of pages16
JournalPlant Journal
Volume101
Issue number4
DOIs
Publication statusPublished - 1 Feb 2020

Bibliographical note

Funding Information:
MDK acknowledges support from the ARC Discovery Grant (DP190101823), the Australian Research Council Centre of Excellence for Climate Extremes (CE170100023) and the NSW Research Attraction and Acceleration Programme.

Funding Information:
MDK acknowledges support from the ARC Discovery Grant (DP190101823), the Australian Research Council Centre of Excellence for Climate Extremes (CE170100023) and the NSW Research Attraction and Acceleration Programme.

Publisher Copyright:
© 2019 The Authors The Plant Journal © 2019 John Wiley & Sons Ltd

Keywords

  • Earth system modelling
  • leaf internal CO transfer
  • photosynthesis
  • plant gas exchange
  • transpiration

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