Effects Of Post-fire Black Carbon Input On Soil Nitrogen Mineralization And Nitrous Oxide Emission In Larix Gmelinii Forest

Nitrogen in soil mainly exists in organic form,and plant growth mainly depends on inorganic nitrogen or some simple nitrogen-containing organic compounds in soil.Soil nitrogen mineralization is the core of soil nitrogen cycle and the main process of controlling plant available nitrogen,which affects the nitrogen balance in the ecosystem Fire is one of the important ecological factors affecting the carbon and nitrogen cycle of forest ecosystem.Under the condition of global warming,the frequency and intensity of forest fire area will increase,which will further increase the accumulation of forest black carbon.Black carbon is a highly inert substance with strong adsorption,which can increase soil nutrients and has great potential in reducing greenhouse gas emissions such as CH₄ and N_XO.Therefore,it is urgent to understand the effect mechanism of black carbon input after fire on soil nitrogen cycling and transformation in forest ecosystem.Therefore,the burning ground of Larix gmelinii forest in Bila River in the Greater Khingan Mountains was selected as the research object,and the unburned plot（C）was selected.Low intensity burn sample（L）and high intensity burn sample（H）,with different levels of black carbon input(black carbon removal and surface humus（Bq）zero level black carbon input（B0）,respectively Low level(5t.hm^-2)black carbon input（B5）,high level(10t.hm^-2)black carbon input（B10）),resin core method and static box gas chromatography were used to investigate fire interference The effects of black carbon input and post-fire black carbon input on soil nitrogen mineralization and nitrous oxide（N₂O）emission in Larix gmelinii forest and its regulatory mechanism were revealed.The main results are as follows:（1）In the case of fire disturbance,the effects of different fire disturbance intensity on soil mineralization rate(R_min)and soil N₂O emission were small,which would lead to soil R_minslowing down the increase of soil N₂O emission The mean value of R_min in upper and lower soil was significantly decreased by 30.72%-38.98%（P<0.05）,and the emission of soil N₂O was increased by 41.3%-115.16%.Under the effect of fire interference,soil temperature（ST）,total nitrogen（TN）and nitrogen leaching amount mainly affected soil R_min,while soil p H,TN mainly affects soil N₂O emission.Therefore,fire disturbance can significantly inhibit soil nitrogen mineralization and promote soil N₂O emission.（2）Under black carbon input,different levels of black carbon input have little difference on soil R_min and N₂O emission,which will lead to the decrease of soil R_min.Removing black carbon and surface humus and low level of black carbon input will reduce soil N₂O emission,while high level of black carbon input will increase soil N₂O emission.After black carbon input,the mean R_min of upper and lower soil decreased by 24.40%-39.09%,and N₂O emission decreased by 3.97%-7.03%and increased by 42.65%.Under the influence of black carbon,soil water content（SWC）,total organic carbon（TOC）,inorganic nitrogen（TIN）,microbial biomass nitrogen（MBN）,soil nitrogen leaching amount and soil TN mainly affect soil R_min,while soil p H,TOC,TN and TIN mainly affect soil N₂O emission.Therefore,black carbon input has no significant inhibition effect on soil nitrogen mineralization,but has no significant promotion effect on soil N₂O emission.（3）Under the black carbon input after fire,the effects of different levels of black carbon input after different intensity fire interference on soil R_min were significantly different,and the effects on soil N₂O emission were little different.However,both of them reduced soil R_min and increased soil N₂O emission by 25.25%-120.02%.The R_min of high level black carbon input after fire interference and black carbon removal after high intensity fire interference and surface humus soil significantly decreased by 50.14%～60.77%（P<0.05）.Soil R_min under low level black carbon input after fire interference is higher than that under high level black carbon input after the same intensity fire interference,while soil N₂O emission under high level black carbon input is higher than that under low level black carbon input.Therefore,black carbon can be appropriately added in forest to promote tree growth under the combined action of fire and black carbon,and soil TN,TOC and soil nitrogen leaching amount mainly affected soil R_min,while soil p H,TN,MBN and soil nitrate nitrogen（NO₃^--N）mainly affected soil N₂O emission.It can be seen that post-fire black carbon input had different effects on soil nitrogen mineralization and had different degrees of inhibition,but had no significant promotion effect on soil N₂O emission.In conclusion,this study selected the soil of Larix gmelinii forest in the Greater Khingan Mountains as the research object to systematically clarify the effects and characteristics of post-fire black carbon input on soil nitrogen mineralization and nitrous oxide emission.However,the effects of fire and black carbon on soil nitrogen cycle are a complex process,including both short-term direct effects and long-term indirect effects.Therefore,long-term,continuous and in-depth observation and research are needed to fully and accurately understand the influence of black carbon input on soil nitrogen mineralization and nitrous oxide emission after fire.Only in this way can we fully understand the relationship between fire and black carbon on soil nitrogen transformation and soil nitrogen supply capacity of Larix gmelinii forest,and also provide important scientific basis for sustainable forest management.