WIDESPREAD CAPACITY FOR DENITRIFICATION ACROSS A BOREAL FOREST LANDSCAPE

Area of Science:

• Environmental Science
• Soil Science
• Microbial Ecology

Background:

• Warming climates and increased fires are causing permafrost thaw, releasing carbon and nitrogen.
• The fate of nitrogen (N) following permafrost thaw is poorly understood, particularly the role of denitrification.
• Denitrification can release nitrogen as nitrous oxide (N$_{2}$O) or nitrogen gas (N$_{2}$), impacting the high-latitude nitrogen cycle.

Purpose of the Study:

• To quantify the microbial capacity for denitrification and N$_{2}$O production in various boreal ecosystems.
• To assess the factors influencing denitrifying enzyme activity (DEA) in Interior Alaska.
• To understand the implications of nitrogen loss via denitrification for carbon storage in permafrost-affected regions.

Main Methods:

• Used anoxic carbon (C)- and nitrogen (N)-amended assays to measure denitrification and N$_{2}$O production.
• Quantified microbial capacity in boreal soils, lakes, and streams.
• Assessed correlates of denitrifying enzyme activity (DEA) across different landscape positions and soil properties.

Main Results:

• Riparian soils and stream sediments exhibited the highest denitrification rates, followed by upland soils, with lakes showing lower rates.
• Deep permafrost soils demonstrated minimal denitrification potential.
• Denitrifying enzyme activity (DEA) was negatively correlated with ammonium pools and positively correlated with organic matter content within landscape positions.

Conclusions:

• Denitrification is a significant pathway for nitrogen loss in boreal forest ecosystems affected by permafrost thaw.
• Widespread nitrogen loss through denitrification may limit the ability of nitrogen-limited primary producers to retain carbon in soils.
• Understanding these nitrogen dynamics is crucial for predicting the future carbon balance of Arctic and boreal regions.