| At present,China is faced with the dual problems of sludge treatment and disposal in municipal sewage treatment plants and urgent restoration of degraded soil.Applying municipal sludge as fertilizer to degraded soil can effectively improve soil quality and realize the resource utilization of sludge.In this study,the effects of different proportions of sludge(0%,2%,5%,10%,15%,30%)and nitrogen and phosphate fertilizers on soil chemical properties,enzyme activities and functional diversity of microbial communities were studied by laboratory culture experiments with sludge from Xi ’an Municipal Sewage Treatment Plant and loess soil from Wang maogou watershed in northern Shaanxi.The changes of soil carbon,nitrogen,phosphorus and enzyme activity stoichiometric characteristics with culture time were discussed,and the driving mechanism of soil ecological stoichiometric characteristics under the condition of sludge addition was revealed,which laid a theoretical basis for the land use of urban sludge.The main conclusions are as follows:1.From the point of view of culture time,the contents of TOC,total nitrogen,total phosphorus,ammonia nitrogen,nitrate nitrogen and available phosphorus in 8 treatments all showed a decreasing trend;From different treatment points of view,the above 6 indexes were significantly increased with the increase of sludge addition ratio.The contents of each index after WN5 treatment were 2.07,1.14,1.66,1.09,1.19,1.19 times that of nitrogen treatment,and 2.07,1.73,1.24,1.32,1.46,1.46 times that of phosphate treatment,respectively.For soil C/N,C/P and N/P,they all increased with the increase of sludge addition at the same incubation time,and all reached the maximum value when the sludge addition was 15%(WN4).2.From the point of view of culture time,the activities of β-1,4-glucosidase(BG),leucine aminopeptidase(LAP),β-1,4-N-acetylglucoaminosidase(NAG)and alkaline phosphatase(AP)increased significantly.From different treatment angles,the activities of the above four enzymes were significantly increased with the increase of sludge addition ratio,and the highest activities of the enzymes in WN5 treatment were 9.77、7.97、10.30 and 1.78 times of those in the control group,respectively.However,the enzyme activity of N and P treatments was not more than 1.1 times that of the control group.The soil enzyme activity measurement ratio Ln BG/Ln(NAG+LAP),Ln BG/Ln AP and Ln(NAG+LAP)/Ln AP increased significantly with the increase of the sludge addition ratio,and WN5 treatment had the best effect on the improvement of these three ratios.It was significantly better than N and P treatments.After adding different proportion of sludge treatment,the cumulative enzyme activity C/N was significantly increased,and C/P showed an increasing trend,while N/P was significantly decreased.3.The Average well color development(AWCD)、Shannon index(H)、Simpson index(Ds)、McIntoh evenness index(U)and richness index(E)were significantly increased with the extension of culture time.AWCD、U、E and the utilization of microbial carbon sources increased significantly with the increase of sludge addition ratio.AWCD and U values of WN5 treatment were significantly higher than those of the other 7 treatments,and the highest values were 8.51 and 2.49 times of those of the control group,4.10 and 2.49 times of those of nitrogen treatment,and 4.78 and 2.28 times of those of phosphate treatment.The utilization of six kinds of carbon sources by microorganisms was dominated by carbohydrates and amino acids,with the highest proportion of 69.77%.4.After adding different levels of sludge,the main controlling factor of soil C/N and C/P was ammonia nitrogen,while the main controlling factor of soil N/P was nitrate nitrogen.The main controlling factor of soil enzyme activity ratio of Ln BG/Ln(NAG+LAP),Ln BG/Ln AP and Ln(NAG+LAP)/Ln AP was nitrate nitrogen.The main controlling factor of AWCD is organic carbon,the main controlling factor of H and Ds is nitrate nitrogen,the main controlling factor of U is available phosphorus. |
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