Nutrient loading of a forest soil : A manipulative approach using rooted experimental chambers

Area of Science:

• Forest Ecology
• Soil Science
• Environmental Chemistry

Background:

• Forest ecosystems face increasing nitrogen (N) deposition from anthropogenic sources.
• Understanding the effects of different nitrogen forms (ammonium and nitrate) on soil nutrient dynamics is crucial for forest health.
• Norway spruce stands are significant components of European forest landscapes.

Purpose of the Study:

• To investigate the impact of ammonium and nitrate addition on mineral-N species and cation leaching in a Norway spruce forest.
• To assess the soil's ability to buffer changes in nutrient leaching under increased nitrogen loading.
• To analyze the relationship between nitrification and the loss of cations like calcium, magnesium, and sodium.

Main Methods:

• Establishment of experimental chambers (rooted and non-rooted) in a Norway spruce stand.
• Supplementation of replicates with ammonium and nitrate over a 17-week period.
• Analysis of leachate to monitor mineral-N species and cation concentrations.

Main Results:

• Ammonium treatments resulted in a 300% greater leaching of calcium and magnesium compared to control treatments.
• The onset of nitrification in ammonium-treated soils correlated with reduced sodium losses.
• These findings suggest a decrease in the soil solution's cation exchange capacity following nitrification.

Conclusions:

• Increased nitrogen loading, particularly as ammonium, significantly enhances the leaching of essential cations (calcium, magnesium) from forest soils.
• Nitrification plays a role in altering soil solution chemistry and cation exchange capacity, influencing nutrient retention.
• Forest soils exhibit a limited capacity to buffer perturbations caused by elevated nitrogen inputs, highlighting potential risks to ecosystem stability.