Application of a coupled model of photosynthesis, stomatal conductance and transpiration for rice leaves and canopy

Authors: LI, S - Us Forest Service (FS); Fleisher, David; WANG, Z - University Of Maryland; Barnaby, Jinyoung; Timlin, Dennis; Reddy, Vangimalla

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2021
Publication Date: 2/23/2021
Citation: Li, S., Fleisher, D.H., Wang, Z., Barnaby, J.Y., Timlin, D.J., Reddy, V. 2021. Application of a coupled model of photosynthesis, stomatal conductance and transpiration for rice leaves and canopy. Computers and Electronics in Agriculture. https://doi.org/10.1016/j.compag.2021.106047.
DOI: https://doi.org/10.1016/j.compag.2021.106047

Interpretive Summary: Crop models are important tools to estimate the impacts of climate stress on plant production without the need to conduct expensive and time consuming experiments. There are many different ways that crop models developed for the rice plant simulate plant growth and water use. Existing methods may not be accurate enough to accurately mimic all the effects of rising atmospheric carbon dioxide concentration (CO2) on important processes like plant growth and water use. A sophisticated energy balance approach that uses sub-models for photosynthesis, stomatal conductance, and transpiration was evaluated to address this problem. These sub-models were first calibrated using measured data, and then tested using an independent set of data observed at the leaf and whole canopy level from a modern rice cultivar. Results showed the approach gave accurate estimates of photosynthesis and transpiration during several different dates over the growing season. However, the values used in the model needed to account for changes in rice plant age and possible acclimation effects due to high CO2 and temperature. The research showed this methodology has substantial promise for improving rice simulations in the United States and will be of great use for the development and application of decision support tools by scientists and crop consultants in the rice industry.

Technical Abstract: Coupling of leaf-level photosynthesis and stomatal conductance models within an energy balance has been proposed to improve gas exchange predictions in crop models to rising atmospheric carbon dioxide concentration (CO2). To evaluate this approach for rice (Oryza sativa, L.), we evaluated changes in leaf gas exchange model parameters due to CO2, plant age and temperature, and assessed the performance of individual and coupled leaf-level photosynthesis, stomatal conductance, and transpiration models. The coupled model was scaled up to the canopy level using a sunlit /shaded leaf approach and evaluated against soil-plant-atmosphere-research chamber gas exchange data. Result showed that photosynthetic model parameters were relatively constant during earlier growth stages, but declined significantly (25 to 45 percent) from the 50-percent heading to grain filling developmental stages. Individual and coupled models showed good accuracy when predicting measured leaf-level responses. Diurnal canopy net photosynthesis predictions over three separate three-day growth periods were also shown to be accurate (less than 0.02 mol CO2 per squared meter per day relative error). There was a slight overestimation of canopy photosynthesis at elevated CO2 for later growth stages that was likely associated with errors in leaf area index or the lack of methodology for photosynthetic acclimation in the model. Predictions for canopy transpiration rate and leaf-to-air temperature differences were consistent with values reported in the literature. Overall results indicate coupled leaf-energy balance models can be accurately used to predict rice gas exchange processes, but further evaluation for combined response to elevated CO2 at canopy level is needed.