Wet canopy photosynthesis in a temperate Japanese cypress forest.

This article investigates the mechanism and significance of wet canopy photosynthesis during and after rainfall in a temperate Japanese cypress (Chamaecyparis obtuse) forest in Japan, focusing on the role of abaxial (lower) leaf surface wetness. Using three years of continuous ecosystem CO₂ flux measurements via the eddy covariance method combined with an enclosed-path gas analyser, alongside simulations from a soil–vegetation–atmosphere transfer (SVAT) multilayer model, the study found that wet-canopy CO₂ uptake predominantly occurs after rainfall rather than during it. Model comparisons indicated that assuming 50% wetting of the abaxial leaf surface best matched observed net ecosystem exchange (NEE), suggesting partial wetting allows stomata to remain open and sustain photosynthesis despite leaf wetness. These findings highlight the importance of partial abaxial leaf wetness in regulating photosynthesis during wet periods and provide insights for improving ecosystem carbon exchange models under changing climatic conditions.