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The impacts of enhanced nitrogen (N) deposition on the global forest carbon (C) sink and other ecosystem services may depend on whether N is deposited in reduced (mainly as ammonium) or oxidized forms (mainly as nitrate) and the subsequent fate of each. However, the fates of the two key reactive N forms and their contributions to forest C sinks are unclear. Here, we analyze results from 13 ecosystem-scale paired 15N-labelling experiments in temperate, subtropical, and tropical forests. Results show that total ecosystem N retention is similar for ammonium and nitrate, but plants take up more labelled nitrate (Formula: see text%) (Formula: see text) than ammonium (Formula: see text%) while soils retain more ammonium (Formula: see text%) than nitrate (Formula: see text%). We estimate that the N deposition-induced C sink in forests in the 2010s is Formula: see text Pg C yr-1, higher than previous estimates because of a larger role for oxidized N and greater rates of global N deposition.
Gurmesa et al. (Tue,) studied this question.