Research On Thecarbon Components Andphysicochemical Characteristics Of Biochar Madefrom Litters Of Four Typical Trees In Maoer Mountain

Forest fires pose a serious threat to the carbon sink function of northeastern China forests and eventhe boreal forest,it may be prevented in large part by reducing the amount of surface fuel.As a highly stable carbon-rich material produced by pyrolysis of biomass under oxygenlimited conditions,biochar exhibits positive soil amendment,purification and carbon sequestration capabilities.In view of the current situation of soil pollution and the urgent need for biomass soil conditioners or pollutant adsorbents in China,and the positive response to China’s carbon neutrality strategy from the perspective of forests.In this study,fresh litter of Larix gmelini,Pinus sylvestris,Quercus mongolica and Fraxinus mandshurica in Maoer mountain was pyrolysed at 300,400,500,600 and 700℃for 1,2 and 3h respectively to obtain60 biochar species.In order to clarify the changes of physical and chemical properties and carbon components of biochars under different preparation conditions and specific values or ranges;the response of different biochar chemical composition,organic structure and carbon distribution characteristics to the preparation conditions;formation mechanism of biochar properties;application potential of various biochar in soil improvement,pollutant adsorption and carbon fixation.The yield,ash content,ash removal yield,element content(total C,H,O,N and S),O/C atomic ratio,H/C atomic ratio,N/C atomic ratio,ammonia nitrogencontent,nitrate nitrogencontent,available phosphoruscontent,p H,EC,CEC,surface functional group content,cold water dissolvedcarboncontent,hot water dissolvedcarboncontent and alkali dissolvedcarboncontent,carbonate carboncontent,easily oxidized carbon and stable carbon contentweremeasured and calculated separately.The main findings are as follows:Pyrolysis temperature was the dominant factor in changing the physicochemical properties of biochars,while retention time had no significant effect on each physicochemical property.As the pyrolysis temperature increased,the phytogenic macromolecular structures of the four types of biochar,such as cellulose,hemicellulose and lignin,were pyrolysed in turn and transformed to aromatised stable structures.Therefore,this leads to a continuous decrease in biochar yield,H/C,N/C,O/C atomic ratios,surface functional group abundance and number,easy carbon content and dissolved organic carbon content,and an increase in its ash,half-life and stable carbon content,which in turn leads to an increase in alkalinity and environmental stability of the biochar produced at higher temperatures.The process of elimination of the active structure of biochar is accompanied by the conversion of elements such as N and P into inorganic forms and lost at higher temperatures,the production of aromatic dissolved organic matter and pyrolyzed at higher temperatures,and the possible creation of more pores and collapsing at higher temperatures.As a consequence the biochar obtained at about 400 ° C has high available nitrogen and phosphorus content,EC,CEC,and the proportion of dissolved organic matter with high aromaticity and degree of polymerization.The four types of biochars are similar in terms of yield,ash content,major elemental content,type and relative content of functional groups,CEC,carbon component and their trends with pyrolysis temperature.The differences in the composition of raw materials resulted in two types of coniferous deciduous biochar,Larix gmelini and Pinus sylvestris,with high carbon content and stable carbon content,and two types of broad-leaved deciduous biochar,Quercus mongolica and Fraxinus mandshurica,with high ash content,fast-acting phosphorus content and dissolved organic carbon content.The CEC of Pinus sylvestris biochar is low;the spectral characteristics of the dissolved organic matter fraction of Larix gmelini are significantly different from the other biochars.The physical and chemical properties,carbon component content and dissolved organic carbon spectral characteristics of biochar have some differences in response to pyrolysis temperature and retention time,some dependent variables have the opposite correlation,which is due to their different raw materials.The four biochars pyrolyzed at 400℃,in particular Quercus mongolica,are promising for use as soil biochar fertilisers and soil conditioners because they have the highest quick-acting nitrogen and phosphorus content and cation exchange capacity,provide some nutrients and have good cationic sorption potential for pollutants.The Fraxinus mandshuricabiochar produced at 300-400℃ has a high dissolved organic carbon content,so it may have good bioavailability and the ability to interact with organic matter in the environment.The stable carbon content of biochar produced from needle is high,especially the biochar prepared by Larix gmelinii at 600℃,which has good application prospects as carbon storage materials.In summary,this study shows that pyrolysis temperature and biomass type are the dominant factors in the carbon fraction,physicochemical properties and application prospects of biochar.The use of forest litter to produce biochar is an important new way to reduce the combustible load on the forest surface and to enhance the carbon sequestration capacity and economic and ecological value of forests.