Nitrogen deposition increases sensitivity to drought observed in Swiss forests

•N deposition decreased the growth of European beech in long-term forest observation sites in Switzerland.

•Mortality rates of both beech and Norway spruce trees were increased with N deposition.

•Drought increased the growth reduction of beech at high N deposition.

•N deposition increased the drought sensitivity of Norway spruce mortality.

•Low foliar P concentrations increased the drought sensitivity of beech mortality, which may explain why beech was strongly affected by the drought of 2018/2019 in some regions of Switzerland.

•Diversity and biomass of ectomycorrhizal fungi (EMF) were strongly reduced with increasing N deposition.