Limited ecosystem recovery from simulated chronic nitrogen deposition

Area of Science:

• Ecology
• Biogeochemistry
• Environmental Science

Background:

• Anthropogenic nitrogen (N) deposition causes significant ecosystem changes.
• Ecosystem recovery after reduced N deposition can be slow due to long-lasting impacts and inertia.

Purpose of the Study:

• To investigate recovery patterns in an alpine ecosystem after a 12-year nitrogen (N) addition experiment.
• To identify factors contributing to slow or absent recovery following declines in N deposition.

Main Methods:

• Monitoring plant species composition, microbial abundance, N cycling rates, soil pH, and cation pools.
• Assessing changes over nine years post-cessation of simulated N deposition (0, 20, 40, 60 kg N·ha⁻¹·yr⁻¹).

Main Results:

• Simulated N deposition altered plant communities (increased nitrophilic species, decreased dominant sedges) and soil chemistry (decreased pH and Mg²⁺, increased Al³⁺ and Mn²⁺).
• Nine years post-cessation, only one plant species showed recovery; microbial abundance remained lower.
• Elevated nitrification rates, NO₃⁻ pools, and depressed base cations (Ca²⁺, Mg²⁺) persisted, alongside elevated toxic metals (Al³⁺, Mn²⁺).

Conclusions:

• Long-term legacy effects of N deposition, including altered N cycling and soil chemistry, impede ecosystem recovery.
• Environmental standards for nitrogen deposition must consider these persistent legacy effects for accurate critical load assessments.