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

Abstract

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 O_³ 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.