The impact of drought on total ozone flux in a mountain Norway spruce forest

In order to understand the impact of summer drought on dry deposition of tropospheric ozone (O3), we compared severe and mild drought periods of summer 2018 in a mountain Norway spruce forest at Bílý Kříž, Beskydy Mts. An eddy covariance technique was applied to measure diurnal courses of the ecosystem O3 and CO2 fluxes. Low O3 deposition was recorded in the morning and evening, while the highest CO2 and O3 fluxes were recorded during the central hours of the day. Total O3 deposition during severe drought (soil humidity 13%) was significantly higher than the deposition during the mild drought period (soil humidity 19%). Our data indicate that high vapour pressure deficit and low soil humidity during severe drought led to the stomatal closure, while non-stomatal O3 deposition, associated with chemical reactions of O3 with NO and volatile organic compounds, are responsible for higher total O3 deposition during the severe drought period. Therefore, we assume that under severe drought stomatal O3 uptake decreases but non-stomatal depositions to forest ecosystems substantially increase.