Climate warming reduces soil gaseous nitrogen losses in a temperate forest

Area of Science:

• Environmental Science
• Ecology
• Soil Science

Background:

• Global warming is projected to increase ecosystem nitrogen loss through gaseous pathways.
• Current models forecasting nitrogen loss rely on uncertain lab experiments with limited in situ validation.
• Nitrogen availability is crucial for primary productivity and carbon sequestration.

Purpose of the Study:

• To investigate the in situ effects of warming on soil gaseous nitrogen emissions in a temperate forest.
• To challenge existing ecosystem model assumptions regarding warming and nitrogen loss.
• To determine the mechanisms behind observed changes in nitrogen emissions under warming conditions.

Main Methods:

• Conducted a 6-year in situ experiment involving warming a temperate forest by 2°C.
• Measured over 200,000 soil nitric oxide (NO) and nitrous oxide (N2O) fluxes.
• Utilized an upscaling approach to estimate nitrogen (N2) fluxes.

Main Results:

• Warming significantly lowered soil emissions of NO by 19% and N2O by 16%.
• These reductions were attributed to warming-induced soil drying, which constrained microbial activity.
• Observed changes were not explained by increased nitrogen conversion to N2, leaching, or plant uptake.

Conclusions:

• Findings challenge the assumption that warming alone accelerates ecosystem nitrogen emissions.
• Warming-induced soil moisture loss and altered freeze-thaw cycles can offset temperature effects on nitrogen cycling.
• In situ soil moisture dynamics are critical for accurately predicting terrestrial nitrogen cycle responses to global warming.