Microbial Diversity And Enzyme Activity Of Soil Reclaimed By Hydraulic Dredge Pump In Coal-mining Subsidence Areas

Soil microbial diversity can reflect the fertility of soils ahead, providing early signs of eco-environmental evolution. Soil microbial diversity is the hotspot of soil ecological study. The evolution law of reclaimed soil physical-chemical properties in mining area has been widely and deeply studied. However, research on microbial diversity of reclaimed mine soil is relatively deficient.By means of combining culture-dependent approach and 454-pyrosequencing, this research evaluated the influence of hydraulic dredge pump reclamation on soil microbial quantity, soil enzyme activity and bacterial community diversity. The evolvement and affecting factors of microbial diversity in soils influenced by reclamation were proposed. The major findings are summarized as follows:(1) The amount of microbes showed significant changes among different soil types, with the order of FAR(Farmland/Control)>RMS(Reclaimed Mine Soil)>SMS(Subsided Mine Soil). Mining subsidence led to significant decline in soil microbe amounts. Microbial quantities increased greatly with the reclamation, but RMS still had fewer populations compared with FAR. Differences in microbe amounts among different soil types might be explained by the dissimilar concentrations of soil organic matter(SOM), total nitrogen(TN) and available phosphorus(AP). Microbial quantities in FAR and RMS gradually decreased with the increasing in vertical depth. Microbial quantities in RMS had no evident difference among soil layers. This was due to the profile variability of soil physical properties and nutrients. Microbial quantities in SMS changed irregularly in vertical depth, suggesting that coal-mining collapses caused the vertical distribution heterogeneity of soil microorganism.(2) Activities of soil urease, sucrase, alkaline phosphatase, and catalase distinctly altered with different soil types, with the order of FAR>RMS>SMS. Compared to SMS, the increase of soil enzyme activity achieved significant level in RMS. Enzyme activities in FAR and RMS were gradually lowered with the increasing in vertical depth, while the vertical distribution in FAR varied from one enzyme to another. Enzyme activity correlated significantly or extremely significantly with SOM, TN, AP and water content(P<0.05, P<0.01). Microbial quantities were highly correlated with activities of soil urease, sucrase, and alkaline phosphatase(P<0.05).(3) 454-pyrosequencing obtained 76135 sequences from the V2-V3 region of the bacterial 16 S r RNA gene. Bacterial communities in FAR were more diverse and rich than those in RMS and SMS. Correlation analyses indicated that SOM, TN, and AP were key factors influencing bacterial diversity. Mining subsidence caused soil erosion and fertility degradation, reduced the soil nutrient supplying capacity on bacterial community. Thus, soil bacterial community structures changed from complication to simpleness. Reclamation increased microbial populations and bacterial abundance. Bacterial diversity of RMS was found to be still lower than FAR.(4) 29 bacterial phyla, 54 classes, 87 orders, 164 families, and 383 genera were identified. Predominant phyla were Proteobacteria(29.67%), Chloroflexi(14.85%), Actinobacteria(9.60%), Acidobacteria(8.11%) and Planctomycetes(7.01%). Differences in the abundance of bacterial community among three soil types were visible. Abundance of bacterial flora had significant correlation with soil properties. These results indicated the ecological diversity of bacteria and the selectivity with soil environment. Species abundance can be taken as an effective indicator for the monitoring of mine soil quality.(5) Significant differences in bacterial community structure were found between FAR and SMS. Reclaimed soils presented higher bacterial diversity and more complex community structures than subsided soils. Compared to SMS, bacterial community structures of RMS tended to be recovered, but still differed from that of control. The correlation and redundancy analysis indicated that shifts in bacterial community structure among different environments may be ascribed to changes of water content, SOM and TN caused by mining subsidence and reclamation(6) Microbial quantities had obvious seasonal variations, which were larger in summer and autumn. Enzyme activities differed among seasons, which were higher in summer and autumn. No significant differences were found in bacterial community structures among seasons. Bacterial richness indices were higher in summer and autumn. Bacterial diversity indices tended to be higher in spring and autumn.(7) Mining subsidence caused soil degradation and microflora disturbance. Reclamation resulted in significant decline in microbial population, enzymatic activity and bacterial diversity indices compared to the control. Recovery of soil fertility and microbial diversity requires the improvement of soil physiochemical property and nutrient contents. The integration of hydraulic dredge pump reclamation, soil amelioration and vegetation restoration was suggested.There are 31 charts, 22 tables and 195 references in this dissertation.