CEE Seminar: Canopy Interception - the Influence of Leaf Wetness on Vegetation Water and Carbon Fluxes

Abstract: Canopy interception of rain, dew and fog occurs in ecosystems worldwide. A ubiquitous effect of leaf wetness on plant water balance is the interference of the water droplets with the leaf energy balance, which increases leaf albedo and emissivity and decreases leaf temperature through droplet evaporation. This, in turn, affects the vegetation carbon uptake rate, with potential consequences for the whole global carbon cycle. Here, I use the specific example of dew deposition to understand how leaf wetness affects water and CO2 fluxes of plants. First, I present a simple leaf energy balance that characterizes the effect of deposition and the evaporation of dew on transpiration and carbon uptake. The model is driven by five common meteorological variables and shows very good agreement with leaf wetness sensor data from the Blue Oak Ranch Reserve in California. I explore the tradeoffs between energy, water and carbon balances for leaves of different sizes across a range of environmental conditions. I then present results from a laboratory experiment where Colocasia esculenta leaves were misted with isotopically enriched water to mimic canopy interception. Leaf water isotopes and water potential measurements suggest a ∼ 30 percent decrease in transpiration rate compared to control leaves, which corroborates the results of the model.