Ammonia (NH₃) is the most abundant alkaline gas in the atmosphere and a precursor to ammonium (NH₄⁺) aerosols. NH₃ and NH₄⁺ also deposit to ecosystems, degrading the environment through eutrophication of surface waters and soil acidification. Agricultural activities dominate anthropogenic NH₃ emissions, but significant uncertainties exist on the fate of these emissions further downwind. NH₃ deposition is poorly constrained by observations, in part due to the measurement challenges of gas phase NH₃ itself. To this end, we developed and deployed two laser-based open-path NH₃ sensors over a natural grassland and adjacent deciduous forest canopy at Duke Forest, North Carolina from August to November 2017 to examine NH₃ fluxes in adjacent natural ecosystems. While the site location is relatively clean with respect to local NH₃ emissions, southeasterly winds place it downwind of the intense agricultural emissions in eastern North Carolina. The sensors were mounted on a 44-m tall tower over the forest canopy and on a 2-m tower over the grassland. A MARGA gradient system and NH_x denuders were also available at the site for intercomparison. The forest and grassland sensors demonstrated 10 Hz precision of 0.17 and 0.30 ppbv, respectively. NH₃ fluxes were calculated from the 10 Hz concentration and three-dimensional wind velocity using the eddy covariance method. Preliminary results suggest net deposition of NH₃ onto the forest canopy and weak net emission from the grassland. Mean NH₃ fluxes of -9.2 ng/m²/s and 1.4 ng/m²/s were measured by the forest and the grassland systems over the entire campaign. Diurnal profiles of NH₃ at the forest and the grassland showed both highest deposition and highest emission during the midday. Smaller peaks of fluxes were also observed in the late afternoon. Ongoing analyses examine the potential biogeochemical and micrometeorological drivers of differences in fluxes between the two ecosystems and relationships between fluxes and trajectories of air passing over the upwind agricultural areas. Our results point to variability of NH₃ fluxes among natural ecosystems as an important sub-grid process and source of uncertainty in chemical transport models used for deposition assessments.