Nitrate is an important nitrogen source for Arctic tundra plants

Area of Science:

• Ecology
• Biogeochemistry
• Plant Physiology

Background:

• Plant nitrogen (N) uptake influences terrestrial ecosystem processes, including carbon (C) accumulation.
• Nitrate (NO3-) is a key N form for plants globally, but its role in Arctic tundra has been considered negligible due to low soil concentrations and undetectable nitrification.
• Understanding plant N form availability is crucial for predicting ecosystem responses to environmental change.

Purpose of the Study:

• To re-evaluate nitrate (NO3-) utilization by Arctic tundra plants.
• To quantify the contribution of soil-derived nitrate to tundra plant nitrogen nutrition.
• To assess the implications of nitrate availability for Arctic ecosystem functioning and carbon storage.

Main Methods:

• Utilized a sensitive denitrifier method to analyze plant-tissue nitrate (NO3-) concentrations.
• Employed 15N isotope enrichments to determine nitrate assimilation rates in tundra plants.
• Applied a Bayesian isotope-mixing model to estimate species-specific contributions of nitrate to total leaf N.

Main Results:

• Soil-derived nitrate (NO3-) was detected in Arctic tundra plant tissues.
• Tundra plants demonstrated significant uptake of soil nitrate, comparable to plants in nitrate-rich ecosystems.
• Nitrate assimilation accounted for 4-52% of total leaf N in Alaskan tundra plants, varying by species.

Conclusions:

• Contrary to prior beliefs, Arctic tundra plants can effectively utilize soil nitrate (NO3-) as a nitrogen source.
• The availability of soil nitrate has significant implications for tundra plant community composition and N loss via leaching and denitrification.
• Recognizing nitrate availability is essential for accurately predicting carbon uptake and storage in Arctic tundra ecosystems.