Divergent legacy effects of biochar on nitrous oxide emissions in acidic soils driven by altered microbial N pathways

Abstract

Acidic soils are global hotspots of nitrous oxide (N₂O) emissions, and biochar has been proposed as a promising mitigation strategy. However, most current evidence comes from short-term studies, and the legacy effects and underlying mechanisms remain poorly understood. Here, we collected acidic soil samples from three sites with and without biochar application, representing short-term (3 and 5 years) and long-term (9 years) legacy effects. Using microcosm incubations, isotope-based source partitioning, and microbial analyses, we evaluated N₂O dynamics and their microbial drivers. The short-term legacy effects of biochar significantly reduced N₂O emissions by inhibiting gross N₂O production and enhancing N₂O reduction. This was primarily attributed to reduced nitrification-derived N₂O, increased nosZ gene abundance, and enrichment of taxa carrying the nosZ gene, such as Rhodanobacter and Gemmatimonas. In contrast, long-term legacy effects markedly increased N₂O emissions because biochar suppressed N₂O reduction more strongly than its production. This was linked to reduced nosZ abundance, increased fungal denitrification, and depletion of dissolved organic carbon and denitrifying bacteria. Together, these findings reveal that the legacy effects of biochar on N₂O emissions diverge over time, driven by changes in microbial nitrogen cycling pathways. These results underscore the importance of incorporating temporal and microbial perspectives when evaluating the long-term climate impacts of biochar and developing sustainable soil management strategies.

Keywords

Acidic soils / Biochar / Legacy effects / Nitrous oxide / Isotopocule analysis / Functional genes

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Funding

National Natural Science Foundation of China(42477358)

Fundamental Research Funds for the Central Universities(KJYQ2025037)

RIGHTS & PERMISSIONS

The Author(s)