Denitrifying pathways dominate nitrous oxide emissions from managed grassland during drought and rewetting
E Harris1, E Diaz-Pines2, E Stoll3
1Plant, Soil and Ecosystem Processes Research Group, Department of Ecology, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria. eliza.harris@uibk.ac.at.
Science Advances
|February 6, 2021
Summary
Drought conditions unexpectedly increased nitrous oxide (N2O) emissions from grasslands, primarily through denitrification, not expected aerobic pathways. Rewetting after drought further amplified these N2O emissions, linking climate change to rising atmospheric N2O levels.
Area of Science:
- Environmental Science
- Soil Science
- Climate Science
Background:
- Nitrous oxide (N2O) is a potent greenhouse gas with an accelerating atmospheric growth rate.
- Anthropogenic N2O emissions largely stem from soil nitrogen fertilization, involving nitrification and denitrification.
- Drought-affected soils are typically assumed to be oxygenated, favoring nitrification over denitrification.
Purpose of the Study:
- To investigate N2O emission pathways in drought-affected and rewetting grassland soils.
- To determine the role of microbial pathways in N2O production under varying moisture conditions.
- To assess the contribution of these pathways to the observed increase in atmospheric N2O.
Main Methods:
- High-resolution isotopic measurements of soil N2O.
- Controlled drought and rewetting experiments on managed grassland.
- Analysis of nitrogen-bearing organic matter enrichment in soil microaggregates.
Main Results:
- Denitrification pathways significantly dominated N2O emissions during severe drought, contrary to expectations.
- Drought induced reversible enrichment of nitrogen-bearing organic matter on soil microaggregates, suggesting chemo- or codenitrification.
- N2O fluxes and denitrification contribution were higher during rewetting compared to control plots at similar soil moisture levels.
Conclusions:
- Drought and subsequent rewetting create potent positive feedbacks that enhance N2O emissions.
- These findings explain the accelerating atmospheric N2O growth rate, linking climate change-induced precipitation shifts to greenhouse gas emissions.
- Management practices and climate change mitigation strategies must consider these drought-driven N2O emission dynamics.
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