Rhizosphere Effect on N2O Emission in Response to Carbon Input Depends on Its Dominant Production Pathway in Tea-Planted Soils

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Abstract A microbe-rich rhizosphere is a hotspot for emissions of nitrous oxide (N2O), a potent greenhouse gas. We hypothesized that residue carbon (C) inputs would alter the rhizosphere effect on N2O emissions due to different C limitations for microbes between rhizosphere and bulk soils. To test this hypothesis, we employed 15N 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 mgC kgsoil–1. We demonstrated that a negative rhizosphere effect on N2O 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 N2O 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 N2O production, the rhizosphere effect on nirS/nirK-type denitrifiers primarily regulated that on denitrification-derived N2O emissions. However, in high-RMA soil, where nitrification dominated N2O production, the rhizosphere effect on nitrogen mineralization mainly regulated that on nitrification-derived N2O emissions. Our results indicate that whether the rhizosphere effect on N2O emissions is positive or negative depends on the prevailing N2O production pathway under elevated C input.

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