Forest canopy nitrogen uptake can supply entire foliar demand

Plant canopies intercept, process and potentially assimilate atmospheric nitrogen (N) additions, but the forest-scale effects of canopy processes on N cycling plant nutrition are not clear. Substantial method artefacts scaling issues exist in previous experimental studies which measure relevant fluxes either at (a) natural abundance, (b) via a 15N tracer or (c) by incorporation additional into measured biomass, meaning these often overlooked discounted. Here, working mature Sitka spruce plantation under ambient conditions, we used all three methods independently stand, tree branch scale to assess interception capture, assimilation inorganic deposition biomass. We consistently found that above 70% was unaccounted for (i.e. assimilated, processed beyond detectability, volatilised retained) when passing through canopy, independent assessment method. Using short-term tracers, this retained tissues. Apparent uptake from monitoring ecohydrological sustained consistent, suggesting were sink deposition. Seasonal variation NO 3 - recovery also suggested biological activities influenced transformations ion within canopy. The total amount greater than mean annual litterfall, implying flux supporting turnover When directly biomass did find evidence immediate relocation other parts tree. Our findings suggest our N-limited site, is likely be as important root may limited supplying rather whole Further research area crucial better understand interactions future changes primary production carbon storage forests. A free Plain Language Summary can Supporting Information article.