Simulation of citrus foliar gas exchange across diverse meteorological conditions: application of the optimal stomatal regulation method.

Abstract

Introduction The optimal stomatal regulation theory provides an eco-evolutionary framework for interpreting the trade-off between CO 2 uptake and water loss. This theory postulates that the marginal water cost of carbon gain ( λ=∂E/∂A ) remains approximately constant over short timescales, thereby offering a mechanistic basis for predicting stomatal behavior and gas exchange. Methods In this study, leaf-level meteorological variables and gas exchange parameters of orchard citrus were measured throughout the entire phenological period during 2021-2022. We developed a family of optimal stomatal conductance-based models (OSCMs), comprising six forms: Rubisco-limited forms (OSCvc and OSCvcd), RuBP-regeneration-limited forms (OSCvj and OSCvjd), and combined forms that dynamically select the prevailing biochemical limitation (OSC and OSCd). Results The key parameter λ was estimated daily and averaged over the entire phenological period. Using daily λ inputs, the three models produced stomatal conductance ( g s ) with accuracies ranked as OSCvjd (R 2 = 0.73) > OSCd (0.63) > OSCvcd (0.40). When a long-term constant λ was applied, model performance declined with accuracies ranked as OSCvj (0.66) > OSC (0.52) > OSCvc (0.38). Discussion The OSC model also produced intercellular CO 2 concentration ( c i ) and photosynthesis ( A ) reasonably well (R 2 = 0.78 and 0.48, respectively). Under moderate meteorological conditions (air temperature 30-40 °C and vapor pressure deficit 1-2 kPa), the OSC model showed its best performance with a mean absolute relative error of 35.2% for g s estimation. Overall, the OSCMs provided a mechanistic approach to simulate citrus leaf gas exchange requiring minimal species-specific traits and routine meteorological inputs. This modeling strategy supports rapid assessment of plant physiological status and estimation of foliar carbon-water fluxes in orchard management under subtropical climates.

Code and data availability

The supplied blocks describe citrus leaf gas-exchange measurements (1852 datasets) and OSCM model development, but no data availability statement content, public dataset deposit, or author code URL is present. The only URLs in the text are the article DOI, a cited ResearchGate reference (Cowan & Farquhar 1977), and FAO

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