Prescribed fires or wildfires are common in natural ecosystems. Biochar input during fires can impact soil greenhouse gas (GHG) emissions, including methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). Meadows are functionally important ecosystems due to their large carbon (C) and nitrogen (N) stocks and potential to mitigate GHG emissions. The effects of biochar on meadow GHG emissions may be sensitive to whether it is derived from more than one type of vegetation, especially with N addition and warming. To further our understanding of how input of fire-derived biochar affects meadow soil GHG emissions, especially under the context of N deposition and warming, we conducted this study to examine potential non-additive effects of these factors. We collected soils from meadows dominated by Miscanthus sinensis and Arundinella hirta at Wugong Mountain (Jiangxi, China). Biochar was produced by pyrolyzing the aboveground vegetation of each of the two species at 450 °C for 1 h. Mixed biochar was produced by 1:1 ratio. Soil GHG emissions and N transformations were measured by incubating soils with biochar (control, M. sinensis biochar, A. hirta biochar, mixed biochar) and N addition (control vs. 6 g m−2) treatments at different temperatures (10, 15, 20, or 25 °C). Biochar input consistently increased both CH4 and N2O flux, but only A. hirta and mixed biochar decreased CO2 emission rates. Mixed biochar imposed non-additive effects on cumulative CH4 and CO2 emissions. Biochar decreased soil nitrification rates and increased the temperature sensitivity of soil N2O emission rates. The results indicated that biochar input during fires in meadows impacts soil GHG emissions and N transformations. Input of biochar into meadow soil following fire impacted GHG emissions, and mixing biochar derived from different species imposed non-additive effects on CH4 and CO2 emissions. The variable and non-additive biochar effects on soil GHG emissions showed that fire-induced alterations in meadow soil GHG emissions will depend on the species composition of the local plant community. The effects of biochar on meadow soil GHG emissions after fires should be considered in future budgets of meadow soil GHG emissions and prediction of prescribed fire impacts on meadow ecosystems under the context of N deposition and warming.

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