Soil recalcitrant but not labile organic nitrogen mineralization contributes to microbial nitrogen immobilization and plant nitrogen uptake

Summary

This meta-analysis of 57 15N tracing studies reveals contrasting mineralization pathways for recalcitrant (mineral-associated) and labile (particulate) soil organic nitrogen pools, with fundamentally different consequences for ecosystem nitrogen retention. Recalcitrant nitrogen mineralisation promotes nitrogen conservation through enhanced microbial immobilisation and plant uptake, whilst labile nitrogen mineralisation accelerates nitrogen loss via stimulation of nitrification. The findings suggest that management strategies favouring recalcitrant over labile organic nitrogen cycling could substantially enhance ecosystem nitrogen conservation and reduce loss risk.

UK applicability

The findings are applicable to UK soil management, where soil pH and total nitrogen vary regionally. UK soils tend towards neutral to slightly acidic conditions with moderate precipitation; the study's findings on pH-driven recalcitrant mineralisation and precipitation-driven labile mineralisation suggest potential for targeted management to enhance nitrogen retention in UK arable and grassland systems, though site-specific validation would be warranted.

Key measures

Recalcitrant organic nitrogen mineralisation rate (MNrec), labile organic nitrogen mineralisation rate (MNlab), soil pH, total nitrogen content, microbial nitrogen immobilisation rate, plant nitrogen uptake, gross autotrophic nitrification rate

Outcomes reported

The study quantified rates of recalcitrant and labile soil organic nitrogen mineralisation across 57 15N tracing studies and examined how these pathways affect microbial nitrogen immobilisation, plant nitrogen uptake, and nitrification. It identified soil pH and total nitrogen as master controlling factors and characterised the ecosystem consequences of each mineralisation pathway.

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