Does nitrogen-induced forest carbon sequestration offset agricultural N2O emissions? – A meta-analysis of nitrogen addition effects on carbon sequestration in tree woody biomass

Lena Schulte-Uebbing1, Wim de Vries1,2

1 Environmental Systems Analysis Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands, www.wageningenur.nl, [email protected]
2 Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands

Abstract

Agricultural nitrogen (N) use leads to nitrous oxide (N2O) emissions, which contribute to climate change. However, elevated N deposition may also increase net primary productivity in N-limited terrestrial ecosystems and thus enhance the terrestrial carbon dioxide (CO2) sink. This indirect effect can lead to a considerable reduction of the net climatic impact of agricultural N use.

We performed a meta-analysis on data from 63 forest fertilization experiments to estimate N-induced carbon (C) sequestration in above-ground tree woody biomass (AGWB), a relatively stable C pool with long turnover times. Results show that boreal and temperate forests respond strongly to N deposition and store on average an additional 23 and 12 kg C per kg N in AGWB, respectively. Sub-tropical and tropical forests show much weaker response to N addition (6 and 2 kg C per kg N, respectively).

We estimated global C storage in tree AGWB resulting from agricultural N use by multiplying the C–N responses obtained from the meta-analysis with ammonia (NH3) deposition estimates per forest biome. We thus derive a global C sink of about 84 (47–120) Tg C yr-1 in AGWB, which compensates on average 16 (9–23) % of N2O emissions from agriculture (6.4 Tg N2O yr-1 or 520 Tg CO2-Ceq yr-1). Adding estimates for N-induced C sequestration in soils and below-ground woody biomass obtained by stoichiometric scaling, we estimate total forest C sequestration resulting from agricultural N use at 236 (147–341) Tg C yr-1, or 40 (28–54) % of agricultural N2O emissions.