Maize Crops Face High Stomatal Uptake During High Exposure to Ozone in an Agroecosystem in the United States Corn Belt

Tropospheric ozone (O 3 ) is a phytotoxic air pollutant. The stomatal uptake of O 3 is a substantial sink of O 3 , but it can create oxidative stress within plants, reducing photosynthesis and crop yields. In seasonally dry climates, stomatal regulation causes temporal decoupling between stomatal conductance and atmospheric O 3 concentrations protecting vegetation from high stomatal uptake of O 3 during peak ambient concentrations in the afternoon, but less is known about this temporal decoupling over agricultural fields in continental humid climates. Here, we investigate how maize ( Zea mays L.) ecophysiology impacts O 3 dry deposition and diurnal O 3 exposure‐dose dynamics at an agricultural field in the central Corn Belt of the United States. We measured the field‐scale eddy covariance flux of O 3 using a UV‐absorption based instrument, the NASA Rapid Ozone Experiment (ROZE). The stomatal component of total O 3 flux was estimated with an inversion of the Penman–Monteith equation using observed latent heat flux and a model of stomatal conductance using gross primary productivity. We found that maize stomatal conductance remained high as vapor pressure deficit increased during the afternoon. The diurnal synchrony between O 3 concentrations and stomatal conductance resulted in high stomatal uptake of O 3 during peak O 3 concentrations. The monthly mean stomatal flux reached > 70% of the total O 3 flux to the land surface during high leaf area index. Furthermore, the total deposition velocity of O 3 was tightly coupled with stomatal conductance. Our findings suggest that maize ecophysiology in our field in the Corn Belt of the United States couples high O 3 stomatal uptake with high O 3 exposure. Furthermore, our study demonstrates the first use of NASA ROZE to measure growing season O 3 flux over an agricultural field, and NASA ROZE will be crucial for expanding O 3 flux measurements necessary for studying O 3 dry deposition and field‐scale phytotoxic dose across other fields.