Nitrogen and biochar interactions promote the stabilization of the temperature sensitivity of soil respiration

Abstract Atmospheric nitrogen (N) deposition and climate warming threaten plantation soil organic carbon (SOC) stability. Soil respiration (Rs), the primary pathway for SOC decomposition, remains poorly understood in terms of regulatory mechanisms. Biochar may mitigate N deposition impacts. However, the mechanisms by which the interactive effects of N and biochar influence Rs through soil microbial community structure, enzyme activity and C–N–P cycling processes, as well as the temperature sensitivity (Q10) of Rs under these interactions, remain unclear. This study investigated these issues through a five-year controlled experiment simulating N deposition and biochar addition in a Larix kaempferi plantation, integrating changes in soil C-cycle-related properties and their interactions. The results revealed that low N addition (LN: 50 kg N ha−1 a−1) increased Rs by 7%, while high-N addition (HN: 100 kg N ha−1 a−1) reduced it by 32%. Low and high biochar treatments (C5: 5 t ha−1; C10: 10 t ha−1) increased Rs by 8% and 13%, respectively. N and biochar interactions consistently suppressed Rs, reducing it by 12%−20%. LN, C5 and C10 enhanced Q10, whereas HN decreased it. Additionally, N and biochar interactions stabilized Q10. N addition directly or indirectly inhibited microbial biomass and aggregate stability by elevating available phosphorus and NO3−-N content, while biochar’s potential to promote SOC was constrained by its diminishing effects over time. Both factors collectively influenced Rs through a chemical–microbial interaction network. This study elucidates the cascading mechanisms linking soil microbial-physicochemical-Rs under N and biochar additions, providing insights for managing soil C emissions under rising temperatures.