El Niño drought and heat extremes suppress soil isoprene uptake capacity in the Amazon rainforest

Abstract Soils are recognized sinks for atmospheric isoprene, but their in situ behavior remains understudied, particularly in the Amazon where emissions are globally significant. Here we show how the 2023 El Niño affected the diel and seasonal variation in soil isoprene fluxes. Under non-stress conditions, the soils acted as a persistent isoprene sink, with uptake driven primarily by ambient isoprene mixing ratios, following a diel cycle and peaking during the dry season. Soil organic matter and litter modulated the fluxes by shaping moisture, temperature, and gas-diffusion responses. During the 2023 El Niño dry season, soil moisture below ~20% constrained soil gas exchange, while associated heat extremes further reduced soil respiration and the soils’ isoprene uptake capacity. As climate change intensifies drought and heat extremes, reduced soil isoprene uptake capacity could impact atmospheric oxidation, aerosol formation, and methane lifetime. Incorporating soil isoprene uptake into atmospheric models is essential for quantifying these feedbacks.