Effect Of Biochar Addition On Soil Carbon Pool Dynamics And Enzyme Activities In Restoration Of Coal Mine Wasteland

Long-term coal mining activities have led to the destruction of the soil ecosystem in the mining area,the decline of soil fertility,the loss of carbon sink function,and the change of microbial community structure.At the same time,the coal mine wastelands and coal gangue are huge sources of CO₂ emissions.Biochar has high carbon content,stability,specific surface area and strong adsorption capacity.It has great potential in increasing soil organic carbon content,carbon sequestration and emission reduction,and improving microbial community structure.Previously,the research on biochar mainly focused on farmland soil,while research on the reclaimed soil in mining areas is very scarce.In this study,through lab cultivation experiments,different sources of biochar（rice straw,corn straw,wheat straw）were added to the soil of in different proportions（CK,1%,3%,5%）.The impact of biochar on the various components of soil organic carbon were analyzed,including organic carbon（SOC）,activated organic carbon（ASOC）,dissolved organic carbon（DOC）and carbon pool management index（CPMI）.We explored the variation of the soil CO₂ emission rate and cumulative emission over time under the action of biochar.At the same time,we studied the effect of biochar on the activities of soil extracellular enzymes such asβ-1,4-glucose sucrase（βG）,β-N-acetylglucosaminidase（NAG）and alkaline phosphatase（ALP）.The influence mechanism is combined with the components of soil organic carbon and p H value.The aim is to screen out biochar remediation measures that are helpful for carbon sequestration,emission reduction,and enhancement of soil fertility in mining areas,and provide a reference for the ecological restoration of coal mine reclaimed soil.The main conclusions are as follows:（1）Biochar significantly increased the SOC and ASOC content of coal mine reclamation area.When the application ratio is 5%,the promotion effect on the SOC content was the strongest.The order of the influence of different sources of biochar on SOC content was corn stover>rice stover>wheat stover.The application ratio of biochar had no significant effect on the ASOC content.Rice straw biochar significantly increased the DOC content of the soil,and the DOC content was proportional to the application ratio.The content of DOC in the soil decreased significantly under the application of corn stalk biochar and wheat stalk biochar at low and medium concentration,while the DOC content in soil increased significantly under the application of high concentration.Except for 5%of wheat biochar addition,the other treatments increased the soil carbon pool management index（CPMI）,compared with the control.It shows that the addition of biochar can increase the soil organic carbon content and soil quality in the coal mine reclamation area;（2）The emission rate and cumulative emission of CO₂ under the action of biochar increased significantly.Because the cultivation time is short.Under the conditions of biochar from the same source,as the application ratio increased,the emission rate and cumulative emission of CO₂ gradually increased.There are significant differences in the cumulative CO₂emissions between the biochar treatment groups of different raw materials,and the soil treatment group with corn stover biochar has the highest cumulative CO₂ emissions（3）Applied coal mine reclamation soil,biochar significantly improved the activity ofβG,while inhibiting the activities of NAG and ALP.The three kinds of extracellular enzymes all had significant correlations with soil SOC content and p H value.At the same time,there were significant correlations among the three extracellular enzymes.Among them,βG activity had a significant positive correlation with p H value,while NAG and ALP activities had significant negative correlation with p H value.There was a significant negative correlation between NAG、ALP activities and soilβG activities.It shows that the change of enzyme activity is affected by soil SOC content、p H value and other extracellular enzyme activities under the treatment of biochar.In sum,although the addition of biochar increased carbon dioxide emissions in a short period of time,it also increased the organic carbon content and ASOC in the coal mine reclamation area,and increased the activity ofβ-1,4-glucose.Our results suggest that the addition of biochar has a positive effect on the coal mine reclamation soil.Moreover,biochar derived from corn stover has the best repair effect at an application rate of 5%.