Soil warming opens the nitrogen cycle at the alpine treeline.

Area of Science:

• Ecology
• Biogeochemistry
• Climate Change Research

Background:

• Climate warming impacts nitrogen (N) cycling, particularly in cold, N-poor ecosystems.
• Cold regions are sensitive to accelerated soil N transformations due to rising temperatures.

Purpose of the Study:

• Investigate nitrogen dynamics across the plant-soil continuum under experimental soil warming.
• Assess the effects of a 6-year warming experiment on N availability and plant N uptake at a high-elevation treeline site.

Main Methods:

• Experimental soil warming (+4°C) over six years (2007-2012) at a Swiss high-elevation treeline.
• Monitoring of soil inorganic and dissolved organic nitrogen pools.
• Analysis of foliar nitrogen concentrations and stable isotopes (δ15N) in dominant plant species.

Main Results:

• Initial increase in soil ammonium (NH4+) pools, followed by a decline.
• Increased dissolved organic nitrogen (DON) concentrations and leaching in warmed plots, especially in later years.
• Sustained increase in foliar δ15N values across species, indicating greater N availability and uptake.
• Variable changes in plant N pool sizes, with increases in Pinus and Vaccinium, but decreases in grasses and fine roots.

Conclusions:

• Warming leads to a persistent increase in plant-available nitrogen and cumulative plant N uptake in treeline ecosystems.
• Increased DON concentrations suggest an 'opening' of the nitrogen cycle under global warming.
• Warming may stimulate growth of certain species while increasing nitrogen losses from cold biomes.