D-NESS

Denitrification, the reduction of nitrogen oxides (NO₃⁻ and NO₂⁻) to NO, N₂O and, ultimately, to N₂ gas in soils, constitutes one of the most important mechanism for the removal of reactive nitrogen (Nr) in terrestrial ecosystems. In spite of its importance, denitrification is the least understood process in the N cycle. Current estimates are still uncertain due to controversial measurements and the observed pronounced variability of N trace gas fluxes in space and time, which are due to the variation of environmental factors such as soil and vegetation properties or meteorological conditions. Considering contemporary atmospheric N deposition rates, the available Nr pool in soils may be greater than the capacity for its removal (via denitrification), with important consequences of chronic N enrichment of terrestrial ecosystems.

Emissions from soils, in both natural (6 - 7 Tg N₂O-N yr⁻¹) and agricultural (4.3 - 5.8 Tg N₂O-N yr⁻¹) systems, represent 5670% of all global N₂O sources. Comparisons between N₂O emission in the preindustrial period (the 1860s) and recent decades (2007- 2016) estimate that global soil N₂O emissions have increased from 6.3 ± 1.1 Tg N₂O-N year⁻¹ to 10.0 ± 2.0 Tg N₂O-N year⁻¹. In the case of croplands, soil emissions increased from 0.3 Tg N₂O-N year⁻¹ to 3.3 Tg N₂O-N year⁻¹, accounting for 82% of the total increase, while soil N₂O emissions from predominantly natural ecosystems accounted for 67% of the global soil emissions in the recent decade but showed only a relatively small increase of 0.7 ± 0.5 Tg N₂O-N year⁻¹ (11%) since the 1860s. However, some studies revealed a greater N-induced emission factor and a higher sensitiveness to N input in natural systems, like forests.

Goals

Isotope-based techniques combined with soil microbial composition characterization offers the possibility to deepen our understanding of soil N metabolic pathways and explaining denitrification processes linked to N₂O emissions, one of the most important GHG. The main objective of this proposal is to quantify denitrification processes in a wide range of soils, using a set of combined isotopic techniques (enriched and natural abundance for the determination of isotopocule signatures) coupled with a complete characterization of the functional denitrifier microbial community (active, GeoChip 5.0). Firstly, we aim to describe N₂O patterns across different soil types in different climate zones and uses (cropland and forests), describing their variability (WP1); then, to evaluate N₂ (+N₂O) fluxes in potential conditions (WP2), and to describe each soil according to its potential of total denitrification; and, finally, to characterize all the co-occurring processes, both biotic and abiotic, that could be involved in each N₂O dynamics pattern, both in natural and potential conditions (WP3).

Proyecto PID2021-128488OB-I00 financiado por MCIN/ AEI /10.13039/501100011033/ y por FEDER Una manera de hacer Europa