| With the rapid development of global industry in recent years,the contribution rate of human factors to dust fall continues to increase,resulting in a significant increase in atmospheric dust flux,which seriously affects the terrestrial ecosystem.As a protective layer of soil in desert area,biological soil crust(BSCs)plays an important role in preventing soil erosion and ecological damage.Atmospheric dust pollution has an important effect on soil quality and properties,but there is a lack of research on the effect on BSCs,soil properties below crusts and influence depth.In order to clarify the ecological effects of atmospheric dust fall on BSCs and subsoil in desert areas,this study adopts the space instead of time series methods.Dust fall,different types of BSCs and subsoil samples were collected around a typical coal-fired power plant(Malliantai Power Plant)in the Ningdong Energy Industrial Base.The change characteristics and differences of physical,chemical and biological properties of different types of BSCs and subsoil were systematically analyzed under the influence of atmospheric dust fall.The correlation between heavy metal elements in dust fall and physicochemical properties and enzymatic activities of BSCs and subsoil,and the correlation between bacterial community diversity,structure and soil factors was also studied.It is expected to reveal the possible influence of atmospheric dust fall on the growth and succession process of local BSCs in industrial and mining areas,and to provide a scientific basis for land suitability and ecological restoration in this area.The main research results are as follows:(1)The average values of heavy metal elements Hg,Pb,As,Cd,Cr and Zn of BSCs in the study area did not exceed the screening value of soil pollution risk of agricultural land(pH>7.5),but the average values of Hg,As and Cd exceeded the soil environmental background value in Ningxia.The mean values of Hg and Cd in algal crust were 3.19 and 1.23 times of the corresponding background values,respectively.The mean values of Hg and Cd in the mixed crust were 3.29 and 1.35 times of the corresponding background values,respectively.The mean values of Hg and Cd in moss crust were 3.71 and 1.57 times of the corresponding background values,respectively.(2)The concentration of heavy metals in BSCs from anthropogenic atmospheric dustfall samples was significant higher than that from natural atmospheric dustfall samples.The higher the degree of development,the stronger enrichment ability of heavy metals in different BSCs was,that is,moss crusts>mixed crusts>algal crusts.The content of heavy metals in the biocrustal layer of different types was significantly higher than that in the soil layer.The analysis of variance showed that the accumulation of heavy metals in BSCs was significantly affected by the dust fall type,and the enrichment of Hg,Pb,Cd,and Cr was significantly affected by the development stage of BSCs.Except for Hg,soil depth had a significant effect on the enrichment of the other five heavy metals.However,the interaction of crust development stage,soil depth and dust fall type only significantly affected the enrichment of Pb element.(3)The pollution degree of heavy metals in BSCs and subsoil is different under the background of atmospheric dustfall:The average order of single pollution index in anthropogenic dust fall samples is Hg(3.825)>Cd(1.078)>As(1.212)>Cr(0.856)>Pb(0.603)>Zn(0.530),while that in natural dust fall samples is Hg(2.745)>Cd(1.136)>As(0.832)>Cr(0.665)>Pb(0.627)>Zn(0.438).The comprehensive pollution index showed that the pollution degree of heavy metals in anthropogenic dustfall samples(2.922)was higher than that in natural dustfall samples(2.085).(4)The effect of different sources of atmospheric dustfall on the bulk density and porosity of biocrustal layer is not significant.In the subsoil,the bulk density of BSCs in the anthropogenic dust fall samples was smaller than that in the natural dust fall samples,and the porosity was larger than that in the natural dust fall samples,indicating that the anthropogenic dust fall could promote the development of soil porosity and reduce its bulk density.Different types of BSCs and subsoil particle size is mainly silt,very fine sand and fine sand,the clay and silt contents of BSCs in anthropogenic dust fall samples were higher than those in natural dust fall samples,while the fine and medium sand contents were lower than those in natural dust fall samples,indicating that different types of dust fall would change the particle size distribution of BSCs and subsoil.Three-factor analysis of variance showed that dust fall types,crust development stage,soil depth and their interaction all had significant effects on particle size distribution.(5)Atmospheric dust fall and BSCs succession can significantly reduce the pH and EC of the biocrustal layer,but have little effect on the pH of the subsoil.In addition,atmospheric dust fall can promote the enrichment of soil organic carbon and nutrients and promote enzyme activity of BSCs.With the succession of BSCs,the ability to enrich organic carbon and nutrients is also enhanced,which is showed as the moss crust>mixed crust>algal crust.In terms of soil depth,the organic carbon,nutrient and enzyme activities in the biocrustal layer of various BSCs were significantly higher than those in the subsoil,indicating that BSCs could well fix nutrient elements,promote enzyme activities and help to increase soil fertility.The results showed that dust fall types,crust development stage,soil depth had significant effects on pH,organic carbon,total nitrogen,total phosphorus,alkali-hydrolyzed nitrogen and enzyme activities,but their interaction had no significant effects on them.(6)The a diversity index of algal crusts in anthropogenic dust fall plots was higher than that in natural dust fall plots,and the a diversity index of mixed and moss crusts was lower than that in natural dust fall plots,indicating that with the development of BSCs,dust fall caused by human factors reduced the a diversity of bacterial community.The similarity of bacterial community structure between algal crust and mixed crust is relatively high,but the similarity between them and algal crust is low.The relative abundance of Actinobacteria(24.48%～26.20),Gemmatimonadetes(7.53%～12.49%),Chloroflexi(5.79%～6.54%)and Armatimonadetes(1.22%～1.47%)in anthropogenic dust fall samples was higher than that in natural dust fall samples,while Firmicutes(0.32%～0.66%)and Acidobacteria(8.49%～15.94%)was lower than that in natural dust fall samples.This may be related to the different sources of particulate matter in atmospheric dust fall. |
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