Atmospheric Feedbacks Reverse the Sensitivity of Modeled Photosynthesis to Stomatal Function

Journal Article · Sat Nov 01 00:00:00 EDT 2025 · Journal of Advances in Modeling Earth Systems

DOI:https://doi.org/10.1029/2025ms005177· OSTI ID:3009044

Liu, Amy X; Zarakas, Claire M; Buchovecky, Benjamin G; Hawkins, Linnia R; Cordak, Alana S; Cornish, Ashley E; Haagsma, Marja; Kooperman, Gabriel J; Still, Chris J; Koven, Charles D; Turner, Alexander J; Battisti, David S; Randerson, James T; Hoffman, Forrest M; Swann, Abigail L S

Abstract Stomata 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 by an empirical parameter within the calculation of stomatal conductance, the stomatal slope . Intuitively, represents the marginal water cost of carbon, relating it to the emergent plant property of water use efficiency. Observations show that can range widely across and within plant types in varying environments, and this distribution of is not captured within Earth system models which represent each plant type with a single value. Here we examine how influences photosynthesis using coupled Earth system model simulations by perturbing to observed and percentiles for each plant type. We find that high reduces photosynthesis nearly everywhere, while low has regionally dependent responses. Under fixed atmospheric conditions, low 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. Choice of also influences photosynthetic response to changes in atmospheric carbon dioxide (), with lower and higher modifying total global response to elevated 2x preindustrial by +6.4% and −9.6%, respectively. Our work demonstrates that atmospheric feedbacks are critical for determining the photosynthetic response to assumptions and some regions are particularly sensitive to choice of . Plain Language Summary Plants affect the Earth system's carbon, water, and energy fluxes through photosynthesis and transpiration, regulated by stomata that control gas exchange. Stomatal function controls the water cost per carbon gain for photosynthesis, where lower water cost means less water lost per carbon gain and higher water cost means more water lost. Observations show a range of stomatal function across and within plant types in varying environments which are not captured in Earth system models. In our study, we explored how changes in stomatal function impact photosynthesis using an Earth system model. We find higher water cost generally decreases photosynthesis everywhere while lower water cost has mixed effects, increasing photosynthesis in the Amazon and central North America but decreasing it in boreal Canada. These responses change when we allow the atmosphere to respond to changes on land, mainly due to spatially varying sensitivity to warmer temperature and drier air. Additionally, changes in stomatal function alter photosynthetic response to higher atmospheric carbon dioxide concentrations, with lower and higher water cost changing global photosynthesis by +6.4% and −9.6%, respectively. Our study demonstrates that accounting for atmospheric responses to land changes is critical for understanding the sensitivity of photosynthesis to stomatal function. Key Points Atmospheric feedbacks reverse the direction of photosynthesis sensitivity to stomatal function in the tropics and high latitudes Stomatal function with higher water cost per carbon gain leads to substantially reduced photosynthesis, especially in the tropics The inclusion of atmospheric feedbacks is critical for evaluating stomatal function in land surface models

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: US Department of Energy; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23), Climate and Environmental Sciences Division (SC-23.1 )
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 3009044
• Journal Information: Journal of Advances in Modeling Earth Systems, Journal Name: Journal of Advances in Modeling Earth Systems Journal Issue: 11 Vol. 17
• Country of Publication: United States
• Language: English