| Soil microorganisms are main participants of ecological processes like decomposition of organic matters and mineralization, and perform fundamental are essential to circulation of materials and ecosystem succession. Soil microbial biomass(SMB) and microbial community are important indicators of soil microorganisms. They appear to be sensitive and responsive to anthropogenic activity and changes of environmental conditions, such as soil organic matter, clay, moisture, temperature and hydrology, may serve as an indicator of soil quantity and environmental changes. Dongting Lake is the second largest freshwater lake in China. It is rich in wetland resources and is an important species gene pool. Therefore, Dongting Lake has much representative and typical characters in protection of species diversity and ecology. In this paper, we studied the effects of ecological and environmental restoration( closed-off management and combined amendments of biochar and compost) and changes of relationship between lake and Changjiang River(decrease in grain-sizes of sediment discharged into Dongting Lake and early dry season) on SMB and microbial community in Dongting Lake wetland.In this study, we examined the possible impacts of closed-off management(an ecological natural restoration measures widely employed for many important wetlands, ban on anthropogenic activity,) on SMB, soil bacterial community structure and functional genes of nitrogen cycling in Dongting Lake wetland. Soil samples were collected from management area(MA) and contrast area(CA) in November 2013 and April 2014. Soil properties, microbial biomass carbon(MBC), and bacterial community structure were investigated. The results showed that there were significant differences in soil properties, which may be the results of increases in richness and diversity of birds, fish and wild animals after closed-off management employed. Comparison of the values of MA and CA showed that SMB and bacterial community diversity(base on the results of PCR-DGGE and high-throughput sequencing) of the MA had a significant increase after 7 years closed-off management. The gene copy numbers of 16 S r RNA and nos Z of MA were significant higher than those of CA. the gene copy numbers of ammonia-oxidizing archaea(AOA) and nir K of MA were significant lower than those of CA. However, there was no significant change in the gene copy numbers of ammonia-oxidizing bacteria(AOB) and nir S. Both the results of redundancy analysis(RDA) and the results of Pearson ’s correlation analysis showed SOM and moisture were the two most important factors of soil microbial biomass and bacterial community structure in Dongting Lake wetland.In this study, we examined the soil physic-chemical properties, bacterial community, bacterial 16 S r RNA and functional marker genes of nitrogen cycling of the soil remedied with nothing(S), compost(SC), biochar(SB), mixture of compost and biochar(SBC), composted biochar(SBced) and biochar-composting(SBCing, biochar and biomass mixed and then composting) after the incubation experiment. The results were that all amendment increased the SMB and bacterial community richness(except SB indicated by Chao1 indicator) and diversity, and SBCing and SB had the greatest efficiency and the lowest efficiency. There were also significant differences in gene copy numbers of bacteria 16 S r RNA, nir K, nir S, nos Z, ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB) between different treatments. Ammonium nitrogen, nitrate nitrogen and water-soluble organic carbon were the main facters of the soi l bacterial community. The changes of SMB and soil bacterial community richness and diversity implied that BCing had the greatest efficiency on soil amendment.In this study, we also examined possible impacts of decrease in grain-sizes of sediment discharged into Dongting Lake on the soil microbial biomass(SMB) and bacterial community structure. Soil samples were collected from sixteen study sites where the surface soil was deposited in early stage(before 1970’s) or recently years. Soil properties, SMB, bacterial community structure were measured. The results indicated that the decrease in grain-sizes of sediment discharged into Dongting Lake caused the significant changes in soil texture(clay and silt increased, sand decreased). It also caused the increases in SMB and bacterial community diversity had an obvious change, and the changes in soil texture were the main cause of these changes.In this study, we determined the potential ecological responses of soil microbial biomass(SMB) and the bacterial co mmunity structure in the Dongting Lake wetland(China) to the early dry season by field experiments. We measured the soil properties, SMB and bacterial community structure for samples E0, E20 and E40(for which the dry season arrived early by 0, 20 and 40 days, respectively). The results indicated significant increase s in SMB and bacterial 16 S r DNA gene copy number as the dry season occurred increasingly earlier. The SMB and bacterial 16 S r DNA gene copy number increased for the samples in the following order: E0 < E20 < E40. The bacterial community structure of E40 was more diverse than that of E20, which was similar to that of E0. Both the results of redundancy analysis(RDA) and the results of Pearson’s correlation analysis indicated that the lead time of the dry season was the controlling influence on the SMB and soil bacterial community structure. |
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