Hot moments of N<inf>2</inf>O transformation and emission in tropical soils from the Pantanal and the Amazon (Brazil)

Tropical wetland soils emit large amounts of nitrous oxide (N2O), especially following wetting of drained soil. We investigated seasonally drained wetland soils from the Pantanal and the Amazon, both with a natural high nitrate content and low pH. Here we report the effect of wetting on the production, emission and consumption of N2O on these soils. Intact soil cores were wetted to simulate natural water logging events, and microsensor measurements were used to i) characterize the vertical microscale distribution of O2 and N2O, ii) monitor the accumulation of N2O in the anoxic soil volume, and iii) quantify the N2O efflux out of the soil. Flux chamber measurements of N2O emission confirmed the effluxes calculated from microsensor measurements.The N2O concentration dynamics in the soil cores were characterized by three distinct phases: 1) an initial slow N2O production, 2) a higher N2O production ending abruptly when the supply of NO3- and NO2- (NOx-) was exhausted, and 3) a final phase where the accumulated N2O was reduced to N2. This evolution of the N2O pool in an intact soil core could be accurately simulated by a simple diffusion-reaction model with the presence of O2 and NOx- as determining factors.Approximately one third of the initial NO3- present in the soil was lost as N2O or N2. As the soil was depleted for NO3- by the end of the experiment we suggest that dissimilatory nitrate reduction to ammonia (DNRA) was responsible for reducing the remaining NO3-. © 2014 Elsevier Ltd

Data from: Hotspots of soil N2O emission enhanced through water absorption by plant residue

N2O is a highly potent greenhouse gas and arable soils represent its major anthropogenic source. Field-scale assessments and predictions of soil N2O emission remain uncertain and imprecise due to the episodic and microscale nature of microbial N2O production, most of which occurs within very small discrete soil volumes. Such hotspots of N2O production are often associated with decomposing plant residue. Here we quantify physical and hydrological soil characteristics that lead to strikingly accelerated N2O emissions in plant residue-induced hotspots. Results reveal a mechanism for microscale N2O emissions: water absorption by plant residue that creates unique micro-environmental conditions, markedly different from those of the bulk soil. Moisture levels within plant residue exceeded those of bulk soil by 4–10-fold and led to accelerated N2O production via microbial denitrification. The presence of large (∅ >35 μm) pores was a prerequisite for maximized hotspot N2O production and for subsequent diffusion to the atmosphere. Understanding and modelling hotspot microscale physical and hydrologic characteristics is a promising route to predict N2O emissions and thus to develop effective mitigation strategies and estimate global fluxes in a changing environment