Presentation Information
[ACG64-P04]Development of a Unified Photosynthesis-Hydraulics Module for MIROC-ES2L
*Keiichi Hashimoto1,2, Tomohiro Hajima2, Hiroaki Miura1 (1.Department of Earth and Planetary Science, The University of Tokyo, 2.Japan Agency for Marine-Earth Science and Technology)
Keywords:
ESM,LSM,Photosynthesis
Terrestrial carbon fixation and transpiration are intrinsically coupled processes governed by stomatal conductance (Cowan & Farquhar, 1977). Plants dynamically regulate this trade-off between carbon gain and water loss in response to environmental conditions such as solar radiation, temperature, and the dryness of both the atmosphere and soil (Sperry et al., 2017). In the Amazon rainforest, for instance, vegetation is known to maintain high evapotranspiration rates and even increase photosynthetic activity during the dry season, capitalizing on abundant solar radiation by accessing deep soil moisture (Saleska et al., 2003; Huete et al., 2006). However, state-of-the-art Earth System Models (ESMs) have generally failed to reproduce this seasonal cycle, often simulating a decline in productivity due to modeled water stress (Baker & Spracklen, 2022). This discrepancy may introduce uncertainty into projections of the interaction between the water and carbon cycles under future climate conditions.
The inability of current ESMs to capture these dynamics is largely attributed to the use of empirical soil moisture stress functions (β-factor) that excessively suppress gas exchange as soil moisture declines (Giardina et al., 2025). In MIROC-ES2L (Hajima et al., 2020), the land surface physical component (MATSIRO) and the terrestrial ecosystem/biogeochemical component (VISIT-e) simulate photosynthesis independently to calculate transpiration and carbon fluxes, respectively. This structural separation is ill-suited for representing the tight coupling of carbon and water cycles or the physiological trade-offs plants face.
To address these issues, we have developed and implemented a new photosynthesis component, ATAMI (Assimilation-Transpiration semi-Analytical Model Interface), into MIROC-ES2L. ATAMI is based on the unified theory of photosynthesis and hydraulics proposed by Joshi et al. (2022). The model posits that plants optimize stomatal conductance and photosynthetic capacity to maximize a profit function defined as carbon gain minus the hydraulic costs associated with water transport and the potential failure known as cavitation. This approach allows for a mechanistic representation of how plants balance carbon acquisition against hydraulic risks without relying on arbitrary empirical stress functions.
In the presentation, we will describe the structure of the ATAMI model and its coupling with MIROC-ES2L. We will also report on the initial performance evaluation of the model against observational data and discuss the differences in the simulated Amazonian hydro-climate compared to the standard MATSIRO/VISIT-e configuration.
The inability of current ESMs to capture these dynamics is largely attributed to the use of empirical soil moisture stress functions (β-factor) that excessively suppress gas exchange as soil moisture declines (Giardina et al., 2025). In MIROC-ES2L (Hajima et al., 2020), the land surface physical component (MATSIRO) and the terrestrial ecosystem/biogeochemical component (VISIT-e) simulate photosynthesis independently to calculate transpiration and carbon fluxes, respectively. This structural separation is ill-suited for representing the tight coupling of carbon and water cycles or the physiological trade-offs plants face.
To address these issues, we have developed and implemented a new photosynthesis component, ATAMI (Assimilation-Transpiration semi-Analytical Model Interface), into MIROC-ES2L. ATAMI is based on the unified theory of photosynthesis and hydraulics proposed by Joshi et al. (2022). The model posits that plants optimize stomatal conductance and photosynthetic capacity to maximize a profit function defined as carbon gain minus the hydraulic costs associated with water transport and the potential failure known as cavitation. This approach allows for a mechanistic representation of how plants balance carbon acquisition against hydraulic risks without relying on arbitrary empirical stress functions.
In the presentation, we will describe the structure of the ATAMI model and its coupling with MIROC-ES2L. We will also report on the initial performance evaluation of the model against observational data and discuss the differences in the simulated Amazonian hydro-climate compared to the standard MATSIRO/VISIT-e configuration.