Reviews and syntheses: Soil N2O and NO emissions from land use and land-use change in the tropics and subtropics: a meta-analysis

[摘要] Deforestation and forest degradation in the tropics may substantially altersoil N-oxide emissions. It is particularly relevant to accurately quantifythose changes to properly account for them in a REDD+ climate changemitigation scheme that provides financial incentives to reduce theemissions. With this study we provide updated land use (LU)-based emissionrates (104 studies, 392 N₂O and 111 NO case studies), we determine thetrend and magnitude of flux changes with land-use change (LUC) using ameta-analysis approach (44 studies, 135 N₂O and 37 NO cases) andevaluate biophysical drivers of N₂O and NO emissions and emissionchanges for the tropics.

The average N₂O and NO emissions in intact upland tropical forestamounted to 2.0 ± 0.2 (n = 90) and 1.7 ± 0.5 (n = 36)kg N ha⁻¹ yr⁻¹, respectively. In agricultural soils annualN₂O emissions were exponentially related to N fertilization rates andaverage water-filled pore space (WFPS) whereas in non-agricultural sites aGaussian response to WFPS fit better with the observed NO and N₂O emissions.The sum of soil N₂O and NO fluxes and the ratio of N₂O to NOincreased exponentially and significantly with increasing nitrogenavailability (expressed as NO₃⁻ / [NO₃⁻+NH₄⁺])and WFPS, respectively; following the conceptual Hole-In-the-Pipe model.Nitrous and nitric oxide fluxes did not increase significantly overall as aresult of LUC (Hedges's d of 0.11 ± 0.11 and 0.16 ± 0.19,respectively), however individual LUC trajectories or practices did. Nitrousoxide fluxes increased significantly after intact upland forest conversion tocroplands (Hedges's d = 0.78 ± 0.24) and NO increasedsignificantly following the conversion of low forest cover (secondary forestyounger than 30 years, woodlands, shrublands) (Hedges's d of0.44 ± 0.13). Forest conversion to fertilized systems significantly andhighly raised both N₂O and NO emission rates (Hedges's d of1.03 ± 0.23 and 0.52 ± 0.09, respectively).

Changes in nitrogen availability and WFPS were the main factors explainingchanges in N₂O emissions following LUC, therefore it is important thatexperimental designs monitor their spatio-temporal variation. Gaps in theliterature on N oxide fluxes included geographical gaps (Africa, Oceania)and LU gaps (degraded forest, wetland (notably peat) forest, oil palmplantation and soy cultivation).

[学科分类] 地球化学与岩石