Spatial heterogeneity of ammonia fluxes in a deciduous forest and adjacent grassland

•NH3 flux was measured concurrently over a deciduous forest and adjacent grassland.•Net deposition and emission were observed over forest and grassland, respectively.•NH3 fluxes peaked in middays and afternoons with negligible flux overnight.•Grassland emissions are consistent with soil and vegetation biogeochemical drivers.•Forest canopy acts as a sink of NH3 coming from upwind sources.