Long-Term Simulated Atmospheric Nitrogen Deposition Alters Leaf and Fine Root Decomposition

Area of Science:

• Forest Ecology
• Biogeochemistry
• Environmental Science

Background:

• Atmospheric nitrogen deposition is increasing globally, impacting forest ecosystems.
• Nitrogen deposition is linked to enhanced forest carbon sequestration, but the mechanisms are not fully understood.
• Organic matter decomposition and soil carbon accumulation are key processes influenced by nitrogen deposition.

Purpose of the Study:

• To investigate the effects of simulated nitrogen deposition on leaf litter and fine root decomposition in northern hardwood forests.
• To determine the contribution of altered decomposition rates to soil organic carbon accumulation.
• To compare the decomposition dynamics of leaf litter and fine roots under nitrogen enrichment.

Main Methods:

• A 3-year decomposition study using litter bags was conducted in four sugar maple-dominated northern hardwood forests.
• Simulated nitrogen deposition was applied chronically to the study sites.
• Leaf litter and fine root decomposition rates were measured, along with changes in litter chemistry and enzyme activities.

Main Results:

• Nitrogen additions marginally stimulated early-stage leaf litter decomposition, correlating with altered litter chemistry.
• Nitrogen additions inhibited later stages of fine root decomposition, linked to decreased lignin-degrading enzyme activities.
• Slower fine root decomposition resulted in increased root mass retention, estimated to explain 5-51% of nitrogen-induced soil carbon accumulation.

Conclusions:

• Simulated nitrogen deposition has contrasting effects on leaf litter and fine root decomposition.
• Slower fine root decomposition is a significant driver of soil organic carbon accumulation under elevated nitrogen deposition.
• This study highlights the importance of considering fine root decomposition in understanding forest carbon cycling responses to nitrogen enrichment.