Distinct material traits shape soil-dependent N2O responses to Fe-, Ca- and Se-modified biochars.

INTRODUCTION

Modified biochars are widely proposed as amendments for regulating soil nitrogen cycling, yet the material traits that underpin their contrasting effects on nitrous oxide (N2O) emissions remain unclear.

METHODS

We compared unmodified biochar with Fe-, Ca-, and Se-modified biochars in loess and black soils during a short-term incubation. Material characterization was combined with N2O flux measurements, soil pH and inorganic-N dynamics, bacterial community profiling, and qPCR quantification of nosZ, nirK, and nirS.

RESULTS

XPS, Raman, and FTIR analyses showed clear differences in surface elemental composition, carbon structure, and functional groups among the modified biochars. FeBC consistently reduced cumulative N2O emissions in both soils, whereas SeBC increased cumulative N2O emissions in loess soil; all biochar treatments reduced N2O emissions in black soil. Among the measured chemical variables, NH4 +-N showed the closest association with cumulative N2O emissions, while pH and NO3 --N reflected the broader N-transformation environment. FeBC was associated with bacterial community shifts linked to lower N2O emissions, whereas CaBC increased nosZ and nirS abundances in loess soil.

DISCUSSION: The results show that Fe-, Ca-, and Se-modified biochars regulate N2O emissions through distinct material-soil-microbial pathways, with their mitigation potential strongly shaped by soil background. These findings provide a trait-based basis for the soil-specific screening of modified biochars for N2O mitigation.