| Coal mining activities have led to soil structure destruction,nutrient loss and microbial diversity reduction,which poses great challenges to the reclamation of coal mine wasteland.In order to speed up soil reclamation,researchers have developed a variety of soil remediation technologies,but many are too expensive and inefficient to be put into use.Biochar is a carbonrich material formed by pyrolysis of organic waste under hypoxia conditions.It is characteristic of rich pore structure,high specific surface area,high stability and low cost,so it shows broad application prospect in the restoration of degraded soil.In this study,to address low nutrients and poor structure of soils in coal mine,soil samples were incubated for 180 days by adding three different rates(1%,3%,5%)of rice straw biochar(SBC1,SBC2,SBC3),wheat straw biochar(XBC1,XBC2,XBC3)and corn straw biochar(YBC1,YBC2,YBC3),and no addition served as a control(CK).Wet sieving method was used to separate bulk soil into aggregates of different sizes.Organic carbon and nitrogen in different aggregates were Measured.The bacterial and fungal communities in different aggregates were investigated by high-throughput sequencing technology.The main results are as follows:(1)There were differences in pore structure among rice straw biochar?wheat straw biochar and corn straw biochar,corn straw biochar had smoother surface and the most abundant pore.All biochars were constructed based on aromatic ring,but the amounts of surface functional groupwere different.Rice and wheat straw biochar are more aromatized compared with corn straw biochar,while corn straw biochar had higher carbon content,ash content,acid functional group amount.(2)The soil aggregates of 0.053?0.25 mm in the original soil were absolutely dominant.The content of >0.25 mm aggregates increased and the content of <0.25 mm aggregates decreased under biochar treament,which indicated that biochar could promote the transformation of small aggregates to large ones.Biochar addition significantly increased the geometric mean diameter(GMD)and mean weight diameter(MWD),which indicated that biochar could improve the stability of soil aggregates.Moreover,aggregate stability increased with the increase of biochar addition ratio,and YBC3 had the most significant effect.(3)The maximum of contents of organic carbon(SOC)and nitrogen(N)occurred in0.25?2 mm particle size.Biochar addition significantly increased the contents of SOC and N,and C/N ratio both in bulk soil and aggregates,and increased the contribution of soil aggregates with size >0.25 mm to total SOC and N,while reduced the contribution of soil aggregates with size <0.25 mm.Stepwise regression analysis showed that SOC content was significantly correlated with SOC content of >2 mm and <0.053 mm aggregates,soil total nitrogen content was significantly correlated with N content of 0.053?0.25 mm aggregates,and soil C/N ratio was significantly correlated with C/N ratio of <0.053 mm aggregates.This indicated that the aggregate carbon and nitrogen have a good indicative effect on soil nutrients.Correlation analysis showed that soil MWD and GMD were significantly positively correlated with soil SOC,N and C/N ratio,which indicated that the formation and stability of soil aggregates were controlled by the interaction of organic carbon and nitrogen.(4)The results of high-throughput sequencing showed that the bacterial community richness increased with the increase of aggregate size without biochar addition.The addition of biochar increased the diversity of bacterial community in >2 mm aggregates and decreased the richness of bacterial community in each size fraction.As for fungal community,biochar addition decreased the richness of fungal community in >2 mm aggregates and increased the richness of other size fractions,and increased the diversity of 0.053?0.25 mm aggregates.Without biochar addition,the relative abundance of Gemmatimonas,Nitrospirae,Acidobacteria,Acidobacteria?Gp6 decreased gradually with the increase of aggregate size,while the relative abundance of Gammaproteobacteria,Fusarium increased gradually.Biochar changed the composition of microbial community at phylum,class and genus levels.Under biochar treatment,the relative abundance of Acidobacteria in aggregates decreased,which indicated that soil aggregates are in transition from oligotrophic to eutrophic environment.The relative abundance of bacteria involved in soil carbon and nitrogen cycle,such as Proteobacteria,Nitrospirae,Betaproteobacteria,and Deltaproteobacteria in aggregates increased.At the same time,biochar addition increased the relative abundance of Actinobacteria,which was beneficial to aggregate stability,and increased the relative abundance of Chytridiomycota,which was beneficial to the accumulation of nitrogen in aggregates,while decreased the relative abundance of Sphingomonas with aromatic metabolizing ability,and decreased the relative abundance of some plant pathogenic fungi,such as Fusarium.Biochar addition promoted the accumulation of nutrients in soil aggregates,and environmental factors such as nutrients also drove the succession of microbial communities.In summary,as a basic unit of soil structure,soil aggregates can provide a variety of habitats for soil microorganisms.The results showed that there were significant differences in organic carbon content,nitrogen content,C/N ratio and microbial community in different aggregates.Therefore,studying soil biological,physical and chemical properties at the aggregate scale would help to reveal its remediation mechanism.Following biochar addition,the content of carbon and nitrogen in soil aggregates and the diversity of microbial community increased significantly,indicating that the soil properties were greatly improved.Among all treatments,the effect of 5% biochar addition was the most significant.The improvement of soil properties is essential to the restoration of soil function,indicating that biochar addition is an effective measure for soil improvement in post-mining areas. |
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