Global patterns and substrate-based mechanisms of the terrestrial nitrogen cycle

Area of Science:

• Ecology
• Biogeochemistry
• Environmental Science

Background:

• Nitrogen (N) deposition significantly affects ecosystem services.
• The precise mechanisms governing N cycle alterations under deposition remain unclear.

Purpose of the Study:

• To investigate the mechanistic basis of nitrogen's impact on N cycle processes.
• To synthesize current ecosystem N research through empirical, conceptual, and modeling approaches.

Main Methods:

• Review and synthesis of empirical studies and conceptual analyses.
• Analysis of model simulations of ecosystem N cycling.
• Examination of N loading effects on plant uptake, soil retention, and N losses.

Main Results:

• Plant N uptake and soil retention decrease with increasing N loading.
• Dissolved and gaseous N losses, initially low, increase exponentially at high N loading rates.
• Biogeochemical models simulating simultaneous N substrate competition better explain observed N loss patterns than sequential models.

Conclusions:

• The traditional N saturation hypothesis requires revision.
• Future research should focus on quantifying N process responses to substrate availability.
• Integrating measured N saturation response functions into models is crucial for predicting terrestrial N cycle dynamics.