Functional Study Of Biocrusts In Ecological Remediation Of Coal Gangue In Abandoned High-sulfur Coal Mines

In southwest China,coal mining has led to soil pollution and large amounts of gangue accumulation.Recent years people have gradually realized the importance of biocrusts in the restoration of degraded land.Biocrusts are ecosystem engineers and an important ground cover vegetation in mining areas,which plays a meaningful role in the succession and maintenance of stability of the ecosystem.However,there is a lack of research on the ecological function of biocrusts at coal gangue in the abandoned site of high sulfur coal mine all over the world.In this paper,the coal gangue up by abandoned high-sulfur coal mines in Kaili,Guizhou Province were used as the research area.The naturally developed moss biocrusts,algae biocrusts in the coal gangue were selected as the research object.Investigation and identification of the species composition of biocrusts.Effect of biocrusts on coal gangue in abandoned high-sulfur coal mine was evaluated by the measuring of nutrient elements(TN,TP,TK,AK),p H,total sulfur content,heavy metal contents(Cr,Cu,Zn,Ni,Fe,Pb,Mn,Cd),characteristics of heavy metals and bacterial communities in biocrusts and crust-free areas.The main findings are as follows:(1)Biocrusts of coal gangue in abandoned high-sulfur coal mines are mainly dominated by bryophytes with a few algae.Among them,a total of 44 species in 17 genera of 5 families of mosses were found,and there were no Hepaticae.The mosses were dominated by Pottiacea(40.9%)and Bryaceae(29.5%).Bryum Dill.(22.7%),Barbula Hedw(13.6%),Ditrichum Hampe(11.4%)and Dicranella(C.Muell.)Schimp(9.1%)are the dominant genera.Barbula unguiculata Hedw and Bryum algovicum Sendt were found in all the sites.There are three families and three genera of algae,namely Pseudanabaenaceae Leptolyngbya Anagn.et Kom.,Oedogoniaceae Oedogonium Link and Coscinodiscaceae Melosira Agardh.(2)The p H of crust-free areas of coal gangue in abandoned high sulfur coal mine is 2-4,the p H of algae biocrusts is 3-6,and the p H of moss biocrusts is 4-7.The p H of the four sites showed moss biocrusts > algae biocrusts > crust-free areas.And the difference of p H between biocrusts and crust-free areas was significant(P < 0.05).The total sulfur content of crust-free areas was higher than that of biocrusts in all sites.The presence of biocrusts regulate the acidic environment of coal gangue dump and reduce total sulfur content.(3)The nutrient content of gangue in high-sulfur coal mines is poor.The biological crust can significantly increase the content of AK and TK in the surface soil of coal gangue.(4)Biocrusts have good adsorption of heavy metals Cd,Zn,Mn,Cu,Cr and Ni.Among which the moss biocrusts have a strong adsorption capacity for heavy metals Zn,Cd,Cr,Mn and Ni,and algae biocrusts have strong adsorption capacity for Cu.The biocrusts have outstanding ability to fix Fe、Cd、Cr、Cu、Pb and Zn metals in the residual fraction,which is beneficial to reduce heavy metal toxicity.(5)Chao,Shannon,Ace,Sobs and Simpson indexes demonstrated the abundance of bacterial communities: moss biocrusts > algae biocrusts >crust-free areas,and these indices in moss biocrusts were significantly higher than that in crust-free areas(P < 0.05).Actinobacteriota,Proteobacteria and Chloroflexi were the dominant phylum in the highsulfur coal mine bacterial community.Acidothermus,Acidiphilium,Leptospirillum,Sulfobacillus and Sphingomonas were the dominant genera in the high-sulfur coal mine bacteria community.(6)Leptospirillum,Sulfobacillus,Ferrithrix and Acidithiobacillus were the dominant genera of bacteria in crust-free areas,and they showed a significantly positive correlation with total sulfur content(P < 0.001)and a significantly negative correlation with p H(P < 0.01).Sphingomonas were the dominant genera of bacteria in biocrusts.They were significantly correlated with most of the heavy metal residual fraction and had a strong influence on characteristics of heavy metals.In addition,they were positively correlated with p H(P < 0.05)and negatively correlated with total sulfur content(P < 0.05).Sphingomonas may play an important role in the adsorption of heavy metals,raising soil p H and reducing sulfur content in biocrusts.Biocrusts are of great ecological significance for gangue in abandoned high-sulfur coal mines in the early stage of natural succession.They can accelerate the progress of recovery and reconstruction of high-sulfur coal mine gangue piles.In the latest researches,the pioneering role of biocrusts are fully utilized and actively applied to the ecological restoration of gangue in abandoned high-sulfur coal mines.