Effects Of Biochar Addition On Soil Greenhouse Gases Emission And Nitrogen Transformation In Meadow Of Wugong Mountain

The low-altitude?about 1 500 to 1 900 m elevation?and widely-distributed mountain meadow in Wugong Mountain of Jiangxi province,is an important indicative vegetation type for climate change.Mountain meadow soils represent large carbon?C?and nitrogen?N?pools.However,human disturbances and natural factors have made the mountain meadow experienced different degrees of fire during autumn and winter when the herb was withered.In addition,global changes,such as warming and increased N deposition,directly or indirectly affect the health and stability of mountain meadow ecosystems.Therefore,exploring the effect of biochar residue,especially mixed biochar residue,on soil C and N cycle and nutrient fluctuations after fire disturbance in mountain meadow in the context of global warming and increased N deposition,will help us to further understand the response of soil ecosystem of mountain meadow on climate change.We collected mixed soil and its aboveground vegetation from meadow dominant by species Miscanthus sinensis?henceforth"Ms"?and Arundinella hirta?Thunb?.Tanaka?henceforth"Ah"?together in Wugong Mountain meadow.Then aboveground vegetation was pyrolized biochar?450°C,1h?.Four temperature gradients?10,15,20,25°C?levels and two N?NH₄NO₃?additions(control vs.6 g N m^-2)levels were used to simulate warming and increased N deposition,respectively.The addition of biochar?CK,Ms,MIX of Ms and Ah,Ah?were used to simulate residual biochar input after fire.We conducted a laboratory incubation experiment to investigate greenhouse gases carbon dioxide?CO₂?,methane?CH₄?,and nitrous oxide?N₂O?emission rates of soils at days 1,3,8,13,18,23,28,37,46,55,64,75,89,and soil net ammonification,nitrification,and N mineralization rates at day 93.The results showed that:1)biochar addition?Char vs.CK?increased average N₂O emission rates/cumulative N₂O emissions,decreased average CO₂ emission rates/cumulative CO₂ emissions,and weakened average CH₄ absorption rates/cumulative CH₄absorptions.Average N₂O emission rates showed a pattern of CK<?Ms=MIX?<Ah.Average CO₂ emission rates showed a pattern of CK<?MIX=Ah?,there was no difference among three biochar.Average CH₄ absorption rates/cumulative CH₄ absorptions showed a pattern of CK>Ms>MIX>Ah.The cumulative N₂O emissions showed a pattern of Ah>MIX>CK and MIX=Ms=CK.Average CO₂ emissions showed a pattern of CK<MS<?MIX=Ah?.2)N deposition increased average N₂O emission rates.3)The temperature sensitivity(Q₁₀)of cumulative N₂O emissions showed a pattern of?Ms=MIX=Ah?>CK.Q₁₀ of cumulative CO₂ emissions showed a pattern of CK and Ms>Ah,there was no significant difference between mixed biochar and other biochar treatments.4)N deposition showed no significant effect on Q₁₀ of cumulative N₂O and CO₂ emissions?P>0.05?.5)There was a non-additive effect on the average cumulative soil CO₂ and CH₄ emissions,the observed values?mixed biochar,MIX?were significantly different from the predicted values?“Ms+Ah”/2??P<0.05?.6)The addition of biochar?Char vs.CK?increased average net nitrification and ammonification rates and decreased average net N mineralization.Average net nitrification rates was higher in CK than other three types of biochar treatments.On the other hand,average net ammonification rates presented negative values and showed a pattern of Ah>MIX>?Ms=CK?.Average net N mineralization rate showed a pattern of Ms<?CK=MIX=Ah?.7)N deposition reduced average net ammonification and N mineralization rates.8)There was a significant positive correlation between soil N₂O emissions and soil net nitrification or N mineralization rates?P<0.05?.In conclusion,although the addition of biochar promoted soil N₂O emissions,it reduced the Q₁₀ of soil N₂O and CO₂ emissions,and net nitrification rate.N addition increased soil N₂O emissions but decreased soil net ammonification rates and N mineralization rates.Therefore,when predicting the effect of fire disturbance on soil C and N cycle,especially the potential of greenhouse gas emissions in mountain meadow,global climate change,such as climate warming and N deposition must be fully considered.