Reconciling multiple impacts of nitrogen enrichment on soil carbon: plant, microbial and geochemical controls

Summary

This study presents an integrated conceptual framework reconciling contrasting effects of reactive nitrogen inputs on ecosystem carbon dynamics by examining plant, microbial and geochemical mechanisms in a Mongolian steppe grassland. Using long-term field experiments, the authors demonstrate that nitrogen effects on particulate soil carbon are mediated primarily through plant production changes, whilst mineral-associated carbon is substantially altered through nitrogen-induced soil acidification, reduced microbial activity, and changes in pH-dependent mineral-carbon binding. The findings highlight the importance of including microbial respiration and geochemical mechanisms in Earth system models predicting carbon budgets under elevated nitrogen deposition.

UK applicability

These findings may be partially applicable to UK grasslands and pasture systems, particularly where nitrogen deposition or fertiliser application occurs. However, the study was conducted in a semi-arid Mongolian steppe with distinct soil mineralogy and climate; UK soils and ecosystems may respond differently, requiring localised research to validate whether similar acidification and geochemical mechanisms operate.

Key measures

Soil carbon pools (particulate and mineral-associated), plant production, microbial growth, soil pH, iron and aluminium mineral-carbon associations, nitrogen-induced acidification

Outcomes reported

The study quantified effects of long-term nitrogen enrichment on particulate and mineral-associated soil carbon pools in a steppe grassland, identifying distinct mechanistic pathways. Results showed that nitrogen-induced soil acidification reduced microbial growth and altered iron/aluminium-carbon associations, explaining variable impacts of nitrogen on soil carbon across ecosystems.

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