Incorporating Experiment-Based SO₂ Damage to Photosynthesis into Regional and Global Land Process Models

Abstract:  Sulfur dioxide (SO₂) is a major air pollutant that damages terrestrial vegetation. It can suppress photosynthesis through sulfite/bisulfite toxicity and ROS-mediated oxidative stress, promoting stomatal closure and impairing chloroplast photochemistry and carbon fixation, as documented in laboratory and field fumigation studies. Here we develop, to our knowledge, the first observation-based parameterization of SO₂-induced photosynthetic damage, derived from 858 measurements compiled from peer-reviewed SO₂ fumigation experiments. The scheme captures observed relationships between accumulated SO₂ exposure above a concentration threshold, ASTα (α, nmol mol⁻¹), and relative leaf photosynthetic rate across broadleaf trees, needleleaf trees, shrubs, C₃ crops, C₄ crops, C₃ grasses, and C₄ grasses. We implement the parameterization in the Common Land Model (CoLM2024). Global simulations for 2003–2021 indicate that, relative to simulations without SO₂ damage, contemporary SO₂ exposure reduces global photosynthetic rate by ~10%. These results highlight the importance of representing SO₂-induced physiological stress in process-based large-scale models to improve assessment and projection of the global carbon cycle.

Keywords: sulfur dioxide (SO₂); photosynthesis; terrestrial ecosystem; fumigation experiments; parameterization, land surface model