Effects Of Biochar And Nitrogen Fertilizer Addition On Greenhouse Gas Fluxes And The Underlying Mechanism

The increasing greenhouse gas（GHG）emissions induced by anthropogenic activities are the main reason of global warming.Withdrawing GHG emissions and enhancing carbon sink have been considered as the most effective way to mitigate climate change.Biochar,as a promising material for carbon sequestration,in combination with nitrogen（N）fertilizer applied into soil can not only improve soil organic carbon（SOC）sequestration,but also promote plant productivity.Although numerous studies have been conducted to examine responses of soil GHG fluxes to biochar or N fertilizer addition,the combined effects of these two factors are still unclear.In this study,we performed a meta-analysis to explore the general patterns of soil GHG fluxes in response to biochar and N fertilizer amendment and identify the influencing factors.Furthermore,we conducted an incubation experiment to explore how biochar and N fertilizer addition influence the priming effect on SOC decomposition by using carbon stable isotope labeling technology.The main results are as follows:（1）By a global synthesis of 634 observations to acquire an overall tendency of GHG fluxes to biochar and N fertilizer addition,our results showed that biochar addition increased soil CO₂ emission by 10.1%,but decreased N₂O emission by 14.7%.Meanwhile,N fertilizer addition increased soil CO₂ and N₂O emissions by 11.6%and288%,respectively.The combination of biochar and N fertilizer addition exhibited significant positive effect on CO₂（+18.0%）and N₂O（+148%）emissions,but non-significant changes on CH₄ fluxes.As a consequence,the interactive effects of biochar and N fertilizer showed as antagonistic effects.The response of soil GHG fluxes under biochar and N fertilizer amendment was related to the physicochemical properties of soil and biochar,experimental method,the amendment rate of biochar and N fertilizer.（2）The results of our incubation experiment showed that biochar addition accelerated the decomposition of soil organic carbon,resulting in a positive priming effect.The cumulative CO₂ emission was increased with the pyrolysis temperature of biochar.However,biochar incombination with N fertilizer amendment inhibited the decomposition of SOC,illustrating a negative priming effect.The cumulative CO₂emission was decreased with the pyrolysis temperature of biochar.The intensity of priming effect was increased with the addition rate of biochar.Meanwhile,biochar pyrolysed at 300^oC combined with N fertilizer in 1%addition rate has the least cumulative CO₂ emission and priming effect（-25.0%）.In addition,the structural equation model showed that the priming effect was mainly affected by total carbon and soil inorganic nitrogen.In conclusions,the interactive effects of biochar and N fertilizer addition on soil GHG fluxes were the antagonistic interaction.Furthermore,our incubation experiment showed that biochar combined with N fertilizer amendment inhibited SOC decomposition,resulting in a negative priming effect.The priming effect was mainly modulated by total carbon and soil inorganic nitrogen.Our findings provide a scientific foundation for making reasonable strategies towards an extensive biochar application to develop sustainable agriculture and mitigate climate change.