Estimating stomatal conductance and partitioning total ozone uptake over a winter wheat field

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Winter wheat is widely cultivated in Eastern China, but subject to high-level surface ozone exposure. To evaluate the impact of ozone on winter wheat, it is necessary to determine the amount of ozone absorbed via the stomata. The goal of this study was to estimate stomatal conductance and investigate the contribution of stomatal ozone uptake over a winter wheat field during a growing season. We used an eddy-covariance technique and portable ozone exchange chambers to characterize water vapour flux, CO2 flux, and total ozone uptake in an agro-meteorological experimental field station in Eastern China. To estimate stomatal conductance of ozone in winter wheat at canopy level, we compared two existing approaches: 1) integrating the Penman-Monteith equation and gross primary production (GPP); and 2) upscaling the modelling results from a parameterized Jarvis-type leaf stomatal conductance model. The results revealed that both methods were capable of quantifying stomatal ozone conductance, but the latter produced a slightly more accurate result. Model results were thus used to simulate stomatal ozone uptake and to partition total ozone uptake into different pathways. The diurnal mean total ozone uptake was found to vary from 4.1 to 7.4 nmol m−2·s−1, and the stomatal ozone uptake varied from 0.42 to 1.75 nmol m−2·s−1 over the growing season. Stomatal ozone uptake accounted for 9–26% of total ozone uptake in the winter wheat. The results suggest that the proposed modelling upscaling method could be considered as a tool for ozone uptake estimation over the winter wheat field.