Global Ecosystem Nitrogen Cycling Reciprocates Between Land-Use Conversion and Its Reversal

Area of Science:

• Ecology
• Environmental Science
• Biogeochemistry

Background:

• Anthropogenic land-use change profoundly affects ecosystem functions and environmental health.
• Ecosystem nitrogen (N) cycling is critical for food security but its global response to land-use change is unquantified.
• Previous research has not fully elucidated the quantitative impact of global land-use shifts on N cycle dynamics.

Purpose of the Study:

• To quantify the global effect of land-use change on ecosystem nitrogen cycling.
• To identify key drivers influencing nitrogen retention and loss following land-use conversion and reversion.
• To pinpoint geographical hotspots of altered nitrogen cycling.

Main Methods:

• Analysis of 2430 paired observations comparing natural and managed ecosystems globally.
• Utilized structural equation modeling to identify predictors of ecosystem nitrogen retention.
• Examined ratios of nitrification, ammonium immobilization, and nitrate to ammonium to assess N cycle function.

Main Results:

• Conversion of natural to managed ecosystems increases N losses via leaching and gaseous emissions (e.g., nitrous oxide), creating a 'leaky' N cycle.
• Reverting land use to resemble natural states reverses N losses by 108% on average, leading to a more conservative N cycle.
• Changes in soil organic carbon, pH, and C:N ratio were more critical than soil moisture or temperature in predicting N retention.

Conclusions:

• Land-use change significantly disrupts ecosystem nitrogen cycling, increasing nutrient losses.
• Ecosystem restoration can effectively restore nitrogen retention capacity, highlighting the importance of land management practices.
• Hotspots for leaky nitrogen cycles are concentrated in equatorial/tropical regions, Western Europe, the US, and China.