| Soil organic carbon is a very important ecological factor in wetland ecosystem. Soil microorganism and enzyme are the most active components in wetland soil, which could be conducive to the mineralization and decomposition of soil organic matter and soil nutrient cycle. Moreover, Soil microorganism and enzyme are sensitive to reflect the dynamic of soil organic carbon, which are not only closely related with soil carbon cycle but also are the early warning indexes of the variations of soil organic carbon. However, the study on the transformation mechanism of wetland soil organic carbon source-sink function is deficient due to the lack of more comprehensive research combined with soil microbes and enzyme activity and other biological processes. The wetlands of Sangjiang Plain are our country important wetlands. The typical regions as the research object, study soil microbiological characteristics of different wetlands influence on soil organic carbon, which will be significance for understanding carbon sequestration mechanism of wetland. This study was implemented in four typical wetland types including Calamagrostis angustifolia+Salix brachypoda wetland(CSW), Calamagrostis angustifolia wetland(CAW), Carex lasiocarpa wetland(CLW) and Phragmites australis wetland(PAW) in flood plain wetland of Honghe and lakeside wetland of Xingkai Lake national reserve of Sanjiang Plain. The main research aimed to analyze the spatial and temporal variations of soil total organic carbon, activated carbon, microbial community structure and microbial respiration rate and soil enzyme activity as well as their quantitative relationship. These results would provide basic data and theoretical basis for insights the dynamics of soil organic carbon in different wetlands and wetland carbon sequestration mechanism.Results indicated that:1. Soil TOC and DOC, MBC and EOC content decreased with the increase of soil depth in the two research regions. The contents of soil TOC and DOC, MBC and EOC in CAW and CSW were significantly higher than that in CLW and PAW in flood plain wetland(P<0.05). But thecontents of soil TOC and MBC in CLW were significantly lower than that in other wetland types in lakeside wetland(P<0.05). By contrast, the contents of soil TOC, MBC and EOC of the four typical wetlands in lakeside wetland were higher than that in flood plain wetland, but only the soil DOC content in PAW and CSW were higher than that in flood plain wetland.2. Soil total organic carbon and active carbon components were presented significant seasonal variation trend in the four typical wetlands in the two research regions. The concentrations of TOC(exclude CLW in lakeside wetland) and DOC were the highest at early stage of plant growth(May) in all wetlands. The contents of soil MBC and EOC of CAW and CSW in flood plain wetland were the highest at the end stage of plant growth period(October). The contents of soil MBC and EOC of CLW and CSW were the highest at the end stage of plant growth period(October), while the contents of soil MBC and EOC of CAW and PAW in lakeside wetland were the highest at early stage of plant growth(May).3. Significant differences about the proportions of soil active organic carbon components accounting for total organic carbon existed among different wetland types in the different seasons. The proportions of soil DOC/TOC, MBC/TOC and EOC/TOC of the four typical wetlands in flood plain wetland ranged of 0.29-1.33%, 1.56-4.42% and 10.54-33.35% respectively. The proportion of soil DOC/TOC in May was highest, while the proportion of soil EOC/TOC in May was the lowest in flood plain wetland. Soil microbial entropy(MBC/TOC) in May was the highest in CLW and PAW, while the proportion of soil MBC/TOC in October was the highest in CAW and CSW. The proportions of soil DOC/TOC, MBC/TOC and EOC/TOC of the four typical wetlands in lakeside wetland ranged of 0.13-0.51%, 0.57-3.25% and 18.39-40.23%, respectively. The proportion of soil DOC/TOC in May was the highest, but proportions of soil MBC/TOC and EOC/TOC in October were the highest.4. Significant differences of soil microbial community structure were founded in different typical wetlands in the two research regions. Soil microbial quantity decreased with the increase of soil depth in all typical wetlands. It showed bacteria > actinomycetes > fungi, and bacteria quantity was the predominant(64.1- 98.2%). The numbers of bacteria and actinomycetes in July were the largest, and the number of fungi in October was the highest. The maximum of soil microbial amount appeared in July and the minimum value presented in May. Significant difference of the proportion of bacteria, actinomyces, fungi amount accounting for the microorganisms amount were founded among different typical wetlands in the two research regions. Soil microbial quantity in CLW was significantly lower than that in other wetland types(P<0.05). Soil microbial amount of the four typical wetlands in lakeside wetland was higher than that in the corresponding wetland types of flood plain wetland.5. Soil invertase and cellulose enzyme activities in all wetlands decreased with the increase of soil depth, but the catalase activity had no obvious variation trend. For flood plain wetland, soil invertase and cellulase activities in May were the highest, while catalase activity in July was the highest except CSW. Soil invertase and catalase activities in CAW and CSW were significantly higher than that in CLW and PAW(P< 0.05), and significant differences of soil cellulase activity was founded among the four typical wetlands. For lakeside wetland, soil invertase and cellulase activities in May were the highest in the four typical wetlands. And soil invertase, cellulase and catalase activities in CLW were significantly lower than that in other wetland types. Moreover, the maximum soil catalase activity in CLW and CAW appeared in October, while the maximum soil catalase activity in PAW and CSW appeared in July. Soil invertase activity in the four wetlands in lakeside wetland was higher than that in the corresponding wetland typesin flood plain wetlands. For PAW and CAW, soil cellulase activity in lakeside wetland was higher than that in Flood plain wetland. For CLW and PAW, soil catalase activity in lakeside wetland was higher than that in flood plain wetland.6. Soil microbial respiration rate decreased with the increase of soil depth in the four typical wetlands, the maximum value occurred in May for the two research regions. For flood plain wetland, soil microbial respiration rate in CLW and PAW was significantly higher than that in CAW and CSW at the early stage of plant growth period(May)(P<0.05), but it was a reverse change trend at the middle and late stage of plant growth preiod(July and October).Soil microbial respiration rate in CLW was significantly lower than other wetland types at early and late plant growth period in lakeside wetland(P<0.05). Soil microbial respiration rate of PAW, CAW and CSW in lakeside wetland was higher than that in flood plain wetland, and the rate of CLW in lakeside wetland was lower than that in flood plain wetland.7. For the two study areas, correlation analysis showed that it was mutual influence and closely connection among soil DOC, MBC and EOC, which had significant relationship with TOC. The contents of soil TOC, DOC, MBC and EOC were significantly correlated with N, but these contents were significantly or extremely significantly negative correlation with p H and no significant correlation with EC; Soil DOC content had significantly correlation with soil water content. For flood plain wetland, it had significant or extremely significant correlation between TOC and other microbe factors exclude actinomycetes and microbial respiration. Soil DOC had extremely significant correlation with fungi, invertase, cellulase and microbial respiration rate. Soil MBC had extremely significant correlation with actinomycetes, microbial respiration rate, and the three enzyme activities. Soil EOC had significant or extremely significant correlation with actinomycetes, invertase and catalase activity. For lakeside wetland, TOC and DOC, MBC and EOC were extremely significant correlation with bacteria, invertase, cellulase enzyme and microorganism respiratory rate. |
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