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Published on: February 5, 2017
Nitrogen-induced new net primary production and carbon sequestration in global forests
1State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China; School of Natural Resources, Faculty of Geographical Science, Beijing Normal University, Beijing, 100875, China.
Abstract:
Nitrogen (N) deposition and biological N fixation (BNF) are main external N inputs into terrestrial ecosystems. However, few studies have simultaneously quantified the contribution of these two external N inputs to global NPP and consequent C sequestration. Based on literature analysis, we estimated new net primary production (NPP) due to external N inputs from BNF and N deposition and the consequent C sinks in global boreal, temperate and tropical forest biomes via a stoichiometric scaling approach. Nitrogen-induced new NPP is estimated to be 3.48 Pg C yr-1 in global established forests and contributes to a C sink of 1.83 Pg C yr-1. More specifically, the aboveground and belowground new NPP are estimated to be 2.36 and 1.12 Pg C yr-1, while the external N-induced C sinks in wood and soil are estimated to be 1.51 and 0.32 Pg C yr-1, respectively. BNF contributes to a major proportion of N-induced new NPP (3.07 Pg C yr-1) in global forest, and accounts for a C sink of 1.58 Pg C yr-1. Compared with BNF, N deposition only makes a minor contribution to new NPP (0.41 Pg C yr-1) and C sinks (0.25 Pg C yr-1) in global forests. At the biome scale, rates of N-induced new NPP and C sink show an increase from boreal forest towards tropical forest, as mainly driven by an increase of BNF. In contrast, N deposition leads to a larger C sink in temperate forest (0.11 Pg C yr-1) than boreal (0.06 Pg C yr-1) and tropical forest (0.08 Pg C yr-1). Our estimate of total C sink due to N-induced new NPP approximately matches an independent assessment of total C sink in global established forests, suggesting that external N inputs by BNF and atmospheric deposition are key drivers of C sinks in global forests.
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