Biochar amendments increase soil organic carbon storage and decrease global warming potentials of soil CH4 and N2O under N addition in a subtropical Moso bamboo plantation

Background: Nitrogen (N) deposition affects soil greenhouse gas (GHG) emissions, while biochar application reduces GHG emissions in agricultural soils. However, it remains unclear whether biochar amendment can alleviate the promoting effects of N input on GHG emissions in forest soils. Here, we quantify the separate and combined effects of biochar amendment (0, 20, and 40 t???ha???1) and N addition (0, 30, 60, and 90 kg N???ha???1???yr???1) on soil GHG fluxes in a long-term field experiment at a Moso bamboo (Phyllostachys edulis) plantation. Results: Low and moderate N inputs (<60 kg N???ha???1???yr???1) significantly increase mean annual soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions by 17.0%???25.4% and 29.8%???31.2%, respectively, while decreasing methane (CH4) uptake by 12.4%???15.9%, leading to increases in the global warming potential (GWP) of soil CH4 and N2O fluxes by 32.4%???44.0%. Moreover, N addition reduces soil organic carbon (C; SOC) storage by 0.2%??? 6.5%. Compared to the control treatment, biochar amendment increases mean annual soil CO2 emissions, CH4 uptake, and SOC storage by 18.4%???25.4%, 7.6%???15.8%, and 7.1%???13.4%, respectively, while decreasing N2O emissions by 17.6%???19.2%, leading to a GWP decrease of 18.4%???21.4%. Biochar amendments significantly enhance the promoting effects of N addition on soil CO2 emissions, while substantially offsetting the promotion of N2O emissions, inhibition of CH4 uptake, and decreased SOC storage, resulting in a GWP decrease of 9.1%???30.3%. Additionally, soil CO2 and CH4 fluxes are significantly and positively correlated with soil microbial biomass C (MBC) and pH. Meanwhile, N2O emissions have a significant and positive correlation with soil MBC and a negative correlation with pH. Conclusions: Biochar amendment can increase SOC storage and offset the enhanced GWP mediated by elevated N deposition and is, thus, a potential strategy for increasing soil C sinks and decreasing GWPs of soil CH4 and N2O under increasing atmospheric N deposition in Moso bamboo plantations.