| Nitrogen is closely related to the stable development of ecosystems.Scientific and reasonable reclamation work can effectively improve the quality of the soil in the mining area.In order to explore the different reclamation patterns in the reclaimed soil in the mining area and the organic nitrogen components in different reclamation years,this paper takes China's largest open-pit coal mine,Pingshuo Antaibao Open-pit Coal Mine as the research area,six sampling lands,which were unreclaimed soil(CK),reclaimed naturally for 3 years(NRL3),reclaimed using alfalfa pasture for 3 years(AL3),9 years(AL9),21 years(AL21)respectively,and reclaimed using buckwheat for 3 years(BL3)were selected.The law of change and nitrogen conversion is intended to provide a basis for the land reclamation and rational use of reclaimed soil in the Antaibao open pit mine.The research results are as follows:(1)The total nitrogen content of the soil profile decreases with the increase of soil depth,and the value tends to be stable after 40~60cm.At the same soil layer,the total nitrogen content increases with the increases of reclamation years under different reclamation patterns.The content of soil acidolytic nitrogen,ammonium nitrogen and amino sugar nitrogen showed an increase with the increase of reclamation year and a decrease from the top to the bottom of the profile.The average ratio between the nitrogen components to total nitrogen is: non-acidic nitrogen > ammonium nitrogen > amino acid nitrogen / acidolytic unknown nitrogen > amino sugar nitrogen,which are the same in different reclamation years.Ammonium nitrogen and amino acid nitrogen are important organic nitrogen forms in the reclaimed soil of Antaibao mining area.The organic nitrogen components of the grassland soil are higher than the same level of cultivated soil,and the soil layer of 0~20cm is more obvious.There is a significant or insignificant positive correlation between organic matter and total nitrogen in the absence of non-acidic nitrogen.The accumulation of organic matter in grassland mode provides a carrier for the conversion of nitrogen components.(2)Long-term reclamation by planting alfalfa significantly increased the activity of catalase,sucrase and protease in the soil layer of 0~10cm;The increase of urease activity was more in 10~20cm;It also had a positive impact on the rest of the profile(20~60cm).For L-asparaginase and L-glutaminase,the enzyme activity of 0~10cm soil layer was improved under many years of alfalfa planting,but the change rule below 10 cm was not obvious.According to the correlation analysis and redundancy analysis,the contribution rate of the nitrogen components was ranked as sucrase > L-glutaminase > catalase > protease > urease > L-asparaginase.Catalase has the greatest effect on total nitrogen and acidolytic nitrogen.Sucrase has a great influence on the ammonium nitrogen,amino sugar nitrogen and amino acid nitrogen.There was significant correlation between acidolytic unknown nitrogen and urease.And non-acidic nitrogen did not reach a significant correlation with the six enzymes.(3)Through the analysis of soil high-throughput sequencing(16S r DNA)and Alpha diversity analysis of bacterial community,the soil bacterial index and diversity index of the soil were the highest in 21 years alfalfa land,and the lowest in 3 years natural recovery land.The bacterial richness index and diversity index of soil under the grassland reclamation pattern were also significantly higher than those under the cultivated land mode.At the level of phylum,proteobacteria,actinobacteria,firmicutes,planctomycetes,acidobacteria and bacteroidetes are the dominant species of soil bacteria in the reclamation area,and they have obvious response to the change of reclamation year and pattern.Among all the plots tested,the proportion of proteobacteria was between 30% and 40%,which was relatively stable;The proportion of actinobacteria,planctomycetes and acidobacteria in the soil of grassland reclamation pattern was significantly increased and that of firmicutes was significantly decreased compared with the soil of cultivated land pattern.(4)Nitrogen mineralization and nitrification were measured by using Stanford aerobic incubation method and constant temperature culture.And then,the first-order reaction kinetics model and Logistic equation were used to fit the process of organic nitrogen mineralization and nitrification.The results showed that the mineralization rate was the highest in 3 years alfalfa field,and the lowest in 21 years alfalfa field.And mineralization of nitrogen was rapid in the first 7 days and gradually became gentle,tended to be stable to 28 days.The first-order kinetic equations suggested that nitrogen mineralization potential ranged from 89.28 to124.51 mg?kg-1 and that was in the order AL21 > NRL3> AL3 > BL3 > CK > AL9.And mineralization rate constant ranged from 0.022 6 to 0.0519,the range was AL3 > AL9 > CK > NRL3 > BL3 > AL21.There was significantly positive correlation between nitrogen mineralization potential and soil organic matter content(r = 0.91).The soil nitrogen capacity was significantly increased in the long-term reclamation under the grassland mode,and the mineralization process was more stable.(5)The change of nitrate concentration in various soils of reclamation area was roughly the trend of “S” curve and could be divided into three stages which were early stage(0~5 d)-rising stage(5~14 d)-stable stage(14~28 d).Logistic equation fitting results showed that the reclamation period significantly affected the peak of nitrification(the max difference was 6.85 days),the drastic nitrification process in 21 years Alfalfa was intense and short,the process of natural restoration land for 3 years was slow and long;the arable land had a greater rate of nitrification and longer nitrification time than grassland.According to the path analysis,the nitrogen mineralization potential showed a significant or significant positive correlation with C/N,amino sugar nitrogen and L-asparaginase.The direct effect of C/N on soil mineralization potential was the most obvious.But the indirect effect on the mineralization potential is offset.Amino sugar nitrogen and L-asparaginase play an important role in the increase of soil mineralization potential.The p H and non-acidic nitrogen were positively correlated with the net nitrification rate of the soil.The direct effect of p H on the net nitrification rate of the soil was more obvious.The indirect effect of non-acidic nitrogen on the net nitrification rate of the soil was more obvious.In summary,in the reclaimed soil of the Antaibao Open-pit Coal Mine,the pattern of grassland and cultivated land has certain effects on the improvement of soil nitrogen fixation and fertility,especially in the soil of 0~20cm in long-term alfalfa planting(grass mode).The content of some organic nitrogen components,enzyme activity and bacterial community diversity significantly increases,the soil nitrogen storage capacity increases,and it makes the mineralization process more stable,improves soil quality. |
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