Bidirectional ammonia exchange above a mixed coniferous forest.

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Forest Ecology

Background:

• High nitrogen deposition impacts forest ecosystems and ammonia exchange.
• Understanding ammonia bidirectional exchange is crucial for air quality and ecosystem health.

Purpose of the Study:

• To evaluate two canopy compensation point models for simulating ammonia bidirectional exchange over a mixed coniferous forest.
• To assess model performance under high nitrogen deposition conditions.

Main Methods:

• Utilized two models: a static model (stomatal and cuticular flux) and a dynamic model (including desorption and precedent fluxes).
• Derived apoplastic ammonium/hydrogen ion ratio (Gamma) to estimate stomatal compensation point (chi(s)).
• Tested models against 16 time series of measured ammonia fluxes.

Main Results:

• The static model's empirical cuticular resistance descriptions failed to reproduce measured fluxes.
• The dynamic model demonstrated a better match with measurements.
• The dynamic model successfully simulated net ammonia emission during daytime.

Conclusions:

• Dynamic modeling, incorporating leaf desorption and historical fluxes, provides a more accurate representation of forest ammonia exchange.
• Improved models are essential for managing ammonia emissions and understanding nitrogen deposition impacts.