Study On The Characteristics Of Heavy Metals And Microbial Activity In Vetiveria Zizanioides L.with Different Planting Years

In order to investigate the characteristics of heavy metals and microbial activities in Vetiveria zizanioides L.substrate of different planting years,the research object was selected the coal gangue sample plots without V.zizanioides(CK)and the matrix of V.zizanioides community at different ages(5 a,8 a,15 a)in coal gangue mountain of Dahe coal mine in Liupanshui city of Guizhou Province.The combination of field sampling and indoor analysis was used to determine the physical and chemical properties of the matrix,the total amount of heavy metals and the content of the chemical fractions,microbiological properties,soil enzymes,number of microorganisms.Analysis of physicochemical properties,heavy metal content,occurrence morphology and microbial activity in vetiver substrate of different planting years.The main results are as follows:(1)In the 0-50 cm soil layer,the pH range of the unplanted V.zizanioides gangue matrix ranged from 7.25 to 7.82,while the pH of the three plots of V.zizanioides increased slightly compared with CK.However,they are all maintained in the neutral partial alkali range.The water content in the matrix increased with the extension of the planting years,and higher than CK in different degree.The conductivity gradually decreases with the extension of V.zizanioides planting period.In terms of substrate nutrients,total nitrogen,total phosphorus,and organic matter increased with the extension of planting years before planting for 8 years,and began to decrease at 15 years of planting.Both available phosphorus and available potassium increased with the prolonged planting period of V.zizanioides,and the nutrient content of coal gangue matrix was improved.(2)In the 0-50 cm soil layer,the contents of heavy metals Cu,Zn and Cd and Pb and As in 0-10 cm matrix decreased with the extension of V.zizanioides planting years.In general,the five heavy metals Cu,Zn,Cd,Pb and As in the gangue matrix decreased with the extension of V.zizanioides planting years.The correlation analysis of heavy metal content and physical and chemical properties showed that pH had significant negative correlation with Cu and Cd,total phosphorus with Zn and Cd,and available potassium with As.There was a significant negative correlation between available phosphorus and Cd.Other physicochemical properties such as water content,conductivity,total nitrogen,total potassium and organic matter had no significant correlation with heavy metals.There was also significant or extremely significant positive correlation between heavy metals.(3)In the 0-10 cm soil layer,the exchangeable state of Zn and As,the carbonatebound state of Zn and Cd,and the Fe-Mn oxide bound state of Cu increased first and then decreased with the extension of V.zizanioides planting years.The heavy metals Cu,Zn,Cd,Pb and As in the gangue matrix are mainly in the most stable residue state,relatively stable organic bound state and carbonate bound state,with relatively few exchangeable states.There is a significant or extremely significant correlation between the different forms of heavy metals in the matrix and the physical and chemical properties.The residual states of Zn,Cd,Pb and As are significantly positively correlated with the total amount.The organic bound state of Zn and As was also significantly positively correlated with available phosphorus and available potassium.The combined state and residual state of Fe-Mn oxide of Cd were significantly negatively correlated with pH.(4)In the 0-10 cm soil layer,the microbial biomass C,N,soil basal respiration and microbial metabolic entropy in the V.zizanioides substrate of different planting years increased first and then decreased with the extension of planting years.Urease and dehydrogenase activities showed a trend of increasing first and then decreasing with the extension of V.zizanioides planting years,while acid phosphatase and catalase showed "reduced-up-lowering".Overall,the number of microorganisms in the matrix showed bacteria > actinomycetes > fungi.Correlation analysis showed that the microbial biomass C and N were negatively correlated with the total amount of heavy metals;Urease activity was significantly correlated with Pb content,while dehydrogenase,acid phosphatase,catalase,bacteria,fungi and actinomycetes were not significantly correlated with the total amount of these five heavy metals.However,different chemical speciation of heavy metals were significantly or extremely significantly correlated with soil enzyme activity and microbial quantity.