Atmospheric feedbacks reverse the sensitivity of modeled photosynthesis to stomatal function

Stomata on leaves mediate fluxes of carbon and water between terrestrial plants and the atmosphere. These fluxes are governed by stomatal function and can be modulated in many Earth system models (ESMs) by an empirical parameter within the calculation of stomatal conductance, the stomatal slope (g1M). Intuitively, g1M represents the marginal water cost of carbon, relating it to the emergent plant property of water use efficiency. Observations show that g1M can range widely across and within plant types in varying environments, and this distribution of g1M is not captured within ESMs which represent each plant type with a single g1M value. Here we examine how g1M influences photosynthesis using coupled ESM simulations by perturbing g1M to observed 5th and 95th percentiles for each plant type. We find that high g1M reduces photosynthesis nearly everywhere, while low g1M has regionally dependent responses. Under fixed atmospheric conditions, low g1M increases photosynthesis in the Amazon and central North America but decreases photosynthesis in boreal Canada. These responses reverse when the atmosphere responds interactively due to spatially differing sensitivity to increases in temperature and vapor pressure deficit. Stomatal function also influences photosynthetic response to changes in atmospheric carbon dioxide (CO2), with lower and higher g1M modifying total global response to elevated 2x preindustrial CO2 by 6.4% and -9.6%, respectively. Our work demonstrates that atmospheric feedbacks are critical for determining the photosynthetic response to assumptions about stomatal function and some regions are particularly sensitive to choice of g1M.

Submitted to JAMES. Find the preprint here. 

Presentations and Posters given for this work:

  • CESM Land & Biogeochemistry Working Group Meeting | Presentation | Virtual at the Mesa Lab, Boulder, CO | Feb 2025 
  • Annual Graduate Climate Conference | Poster | Pack Forest, WA | Nov 2024
  • DOE EESM PI Meeting | Poster | Rockville, MD | Aug 2024 
  • CESM Land & Biogeochemistry Working Group Meeting | Presentation | Virtual at the Mesa Lab, Boulder, CO | Feb 2024 
  • AGU Fall Meeting | Poster | San Francisco, CA | Dec 2023
  • Annual Graduate Climate Conference | Poster | Woods Hole, MA | Nov 2023
  • Annual CESM Workshop | Presentation | Boulder, CO | Jun 2023
  • CESM Land & Biogeochemistry Working Group Meeting | Presentation | Mesa Lab, Boulder, CO | Feb 2023
  • Annual Graduate Climate Conference | Poster | Pack Forest, WA | Oct 2023