Methane (CH 4 ), uptake by well-drained soils plays a vital role in mitigating atmospheric CH 4 . Previous research has demonstrated that nitrogen (N) addition and rhizosphere processes markedly affect soil CH 4 uptake. However, how rhizosphere activity mediates the response of soil CH 4 uptake to N addition remains unclear. Here, we conducted in-situ measurements of CH 4 fluxes using collar treatments to quantitatively assess the rhizosphere contribution to soil CH 4 uptake in a temperate larch plantation. We further evaluated the effects of N addition level (CK: no N addition; low-level N addition: 20 kg N ha -1 yr -1 ; high-level N addition: 50 kg N ha -1 yr -1 ) and duration (short-term and long-term) on CH 4 uptake. We found that soil CH 4 uptake was insensitive to low-level N addition but significantly reduced by 20.9% under high-level N addition. Notably, rhizosphere CH 4 uptake decreased even under low-level N addition, primarily due to reduced rhizosphere activity in our N-limited plantation. A global meta-analysis further confirmed that N addition below 25 kg N ha -1 yr -1 had no effect on soil CH 4 , whereas higher N levels suppressed it by increasing soil NH 4 + -N and NO 3 - -N accumulation. Both field experiments and meta-analysis found no significant effect of N addition duration on soil CH 4 uptake. Overall, our study highlights the critical role of rhizosphere processes in regulating the soil CH 4 uptake under N addition highlight differential responses to N addition levels, and provide important implications for predicting forest soil CH 4 sinks under future global N deposition scenarios.
Chen et al. (Mon,) studied this question.