Rhizosphere Effect on N ₂ O Emission in Response to Carbon Input Depends on Its Dominant Production Pathway in Tea-Planted Soils

A microbe-rich rhizosphere is a hotspot for emissions of nitrous oxide (N 2 O), a potent greenhouse gas. We hypothesized that residue carbon (C) inputs would alter the rhizosphere effect on N 2 O emissions due to different C limitations for microbes between rhizosphere and bulk soils. To test this hypothesis, we employed 15 N tracing and molecular approaches in two tea-planted soils differing in nitrogen-related rhizospheric microbial abundance (RMA) at residue input rates of 0, 259, and 518 mg C kg soil –1 . We demonstrated that a negative rhizosphere effect on N 2 O emissions in low-RMA soil was significantly diminished under low C input but amplified under high C input. In contrast, a negative rhizosphere effect on N 2 O emissions in high-RMA soil was gradually diminished with increasing C input and shifted to be positive under high C input. In low-RMA soil, where denitrification almost dominated N 2 O production, the rhizosphere effect on nirS / nirK -type denitrifiers primarily regulated that on denitrification-derived N 2 O emissions. However, in high-RMA soil, where nitrification dominated N 2 O production, the rhizosphere effect on nitrogen mineralization mainly regulated that on nitrification-derived N 2 O emissions. Our results indicate that whether the rhizosphere effect on N 2 O emissions is positive or negative depends on the prevailing N 2 O production pathway under elevated C input.