| Long-scale reclamation can cause significant changes to the ecosystem in marshland.The types of vegetation,soil properties and soil microbial community structure and diversity were changed by the reclamation process associated with the farming and the addition of fertilizers and pesticides.This results in varying degrees of degradation in the marsh.In order to quantify the impact of large-scale reclamation on the soil environment in Honghe Marshland in northeast China,in 2015,the soil microbe amounts,soil microbebiomass,microbial community structure,microbial functional diversity and their influencing factors were investigated by the methods of field investigation,microbiological cultivation,Illumina Miseq high throughput sequencing and BIOLOG.The result shows that:1.The soil physicochemical properties of marsh were affected significantly by disturbance of reclamation in Sanjiang Plain.By comparison,soil samples from the cultivated wetland had a relatively high mean pH value with 8.44%higher than that of the primary marsh soil.And the mean soil pH was 2.77%lower than the restored wetland soil.Soil samples from the cultivated marsh had a relatively low mean moisture content with 42.31%lower than that of marsh soil.Soil moisture content was increased significantly after cropland converting to wetland,and the average increase of 22.32%.The levels of soil nutrients were higher in primary marsh soil:soil total carbon,total nitrogen,organic carbon,dissolved organic carbon,alkali-hydrolyzable nitrogen,and C/N ratio were 2.40,1.23,3.31,2.94,1.19,and 1.83 fold higher than those in the cultivated marsh soil,respectively.And they were 1.57,1.12,1.70,2.48,2.29,and 1.46 folds higher than those in the restored wet soil,respectively.2.The catalase,urease,nitrate reductase and dehydrogenase activities of soil were different significantly among different habitats(P<0.05).The levels of soil enzyme activities were highest in primary marsh soil:soil catalase,soil urease and soil nitrate reductase activity were 1.89,1.40,and 1.54 fold higher than that of cultivated marsh.And were 1.23,1.06,and 1.50 fold higher than that of restored wetland.Soil dehydrogenase activity in the cultivated wetland was 113.4%higher than that of the primary marsh,and it was 70.5%higher than that of restored wetland.The catalase,nitrate reductase and urease with the soil nutrients and moisture content shown Significant(P<0.05)or extremely significant(P<0.01)positive correlation.The dehydrogenase,catalase and nitrate reductase activities of soil were mainly affected by soil carbon content in marshland.Soil urease activity was mainly affected by soil water content,while soil cellulase was affected by soil carbon and nitrogen.Thus,the catalase,urease and nitrate reductase activities can be used as indicators of the nutrient status of the wetland in this area.3.The research found that influence of the reclamation and recovery on soil microbe amounts and microbe biomass were significant difference among different habitats(P<0.05).Soil microbe amounts and soil microbe biomass were highest in primary marsh soil:soil fungal amounts,soil microbial biomass carbon and soil microbial biomass nitrogen were 6.82,1.25 and 1.46 folds higher than those in the cultivated marsh soil,respectively.And they were 1.05,2.28,1.61 fold higher than in the restored wetland soil,respectively.The amounts of soil bacteria and actinomycetes in cultivated wetland were 152.9%and 74.4%higher than those in primary marsh,and were 47.8%and 14.1%higher than those in the restored wetland,respectively.Soil microbial activity was significantly correlated with the soil physicochemical factors and enzyme activities in marsh soil.The relationship between soil enzyme activity and soil microbial activity is closely and complex in 3 kinds of habitats.Soil bacteria and actinomycetes were negative correlation with soil water content,soil carbon content,soil nitrogen content,but they were a significant positive correlation with soil pH.The soil fungi and the biomass carbon and nitrogen content of soil microbial were significantly positively related to soil water content,soil carbon and nitrogen content,but they were a significant negatively correlated with soil pH.4.The 358,737 sequences that represented 36 bacterial phyla and 397,322 sequences that represented 6 fungal phyla were obtained from the soils sample in the three kinds of habitats.The dominant bacterial phyla that showed greatest variation among habitat types(>1%of average relative abundance)were Gemmatimonadetes(P<0.01),Bacteroidetes(P<0.01),Firmicutes(P<0.01)and Chlorobi(P<0.01).The two most abundant phyla among the main soil fungi are Ascomycota and Basidiomycota.Basidiomycota(P<0.01),Zygomycota(P<0.01),Glomeromycota(P<0.01)and Chytridiomycota(P<0.01)were different significantly in different habitats.Soil samples have high relative abundance and low relative abundance of soil microbial phyla in different habitats.The arrange order of diversity of the soil bacterial community was "the cultivated land>the wetland restoration area>the pristine marsh".And arrange order of the diversity of the soil fungal community was "pristine marsh>the wetland restoration area>the cultivated land".Using redundancy and correlation analysis method,we demonstrated that chronic disturbance through cultivation,especially dry cultivation,significantly altered the microbial community composition of marsh soil.The a-diversity of the soil bacterial community and soil fungal community were found to be most affected by soil moisture,soil pH,total carbon,soil organic carbon,soil dissolved organic carbon,available nitrogen,microbial biomass of carbon,and microbial biomass of nitrogen.Meanwhile,the composition of the soil bacterial and fungal communities were significantly affected by the soil moisture,soil pH,total carbon,soil organic carbon,and soil dissolved organic carbon.5.The seasonal variation of functional diversity of soil microbial communities was significant difference among 3 habitats.The arrange order of diversity of the soil microbial function in May or November was all "pristine marsh>the wetland restoration area>cultivated wetland".The arrange order of diversity of the soil microbial function in July was"cultivated wetland>the pristine marsh>wetland restoration area".The arrange order of diversity of the soil microbial function in September was "pristine marsh>the cultivated wetland>a minimum in wetland restoration area".The arrange order of diversity of the soil microbial carbon utilization in different habitats was "pristine marsh(18 kinds)>the wetland restoration area(14 kinds)>cultivated wetland(10 kinds)".Soil physicochemical properties and enzyme activities are closely related with the functional diversity of soil microorganisms.So,the soil physicochemical properties and enzyme activity conditions in the primary marsh were better than those of the cultivated wetlands and the wetland restoration areas,indicating that soil microbial functional diversity can indicate and reflect the changes in soil conditions sensitively.In summary,large-scale reclamation have significant impacts on soil physicochemical properties,enzyme activities,microorganism amounts,microbial biomass,microbial community structure and functional diversity in marsh.These indexes can be used as indicators of wetland nutrient status in this area,and used to assess the degradation levels of wetland soil ecosystems.These findings highlight the importance of effectively managing the soil bacterial community in order to maintain a naturally functioning soil ecosystem. |
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