The Degradation Of Typical Aquatic Macrophytes By The Cellulolytic Bacteria And The Exploration Of Wetland Substrate Material Prepared From The Hydrophyte Degradation Residues

Aquatic macrophytes are the primary producers and important biological resources in the wetland ecosystem,as they perform multiple ecological functions,such as provide energy for the organisms in the ecosystem,maintain ecosystem stability,and play a central role in the process of nutrient cycle and energy flow in wetland ecosystem.However,if the harvesting and removal of overgrown aquatic macrophytes were untimely,the dead and decayed macrophytes residue which contain large amount of organic matter and nutrients would produce additional pollution to the wetland ecosystem.Therefore,sound management and effective utilization of aquatic macrophytes resources are urgently needed.In this context,the present study focused on the nutrient contents and fiber fractions analyze in the commonly seen aquatic macrophytes（including submerged macrophytes,floating macrophytes and emergent macrophytes）,and measured the physiological indexes of these plants,and further discussed the potential and feasibility of resource utilization of aquatic macrophytes.Moreover,we isolated and characterized four cellulolytic bacterial strains from Lake Donghu sediments（Wuhan,China）that were rich in organic matter and plant residues,and characterized the endo-glucanase activity of the isolated cellulolytic bacteria.Degradation capability of the screened bacteria on submerged and emergent macrophytes were also further explored.To utilize the residual aquatic plants powder after degraded by screened cellulolytic bacteria to the maximum extent,the carbon-based wetland substrate materials were produced by mixing the residual H.verticillata and C.indica powder with clay and other mineral material.Furthermore,effect of wetland substrate materials on the removal efficiency of pollutants and greenhouse gas emissions in horizontal subsurface constructed wetlands（HSCWs）were studied.In this context,the present study aimed to explore the reduction and utilization of the aquatic macrophytes,and at the same time enrich aquatic macrophytes cellulolytic bacteria strains bank that can efficiently degrade aquatic macrophytes.Besides,the degraded hydrophyte residues were prepared into the carbon-based wetland substrate to turn waste into treasure.The main contents and results are as follows:1.Physiological indexes of 18 kinds of typical aquatic macrophytes were analyzed and compared,and it was found that the crude protein and carbohydrate contents in aquatic macrophytes,especially emergent macrophyte（Arundo donax,Nelumbo nucifera,Thalia dealbata,Typha angustifolia,Acorus calamus,Zizania latifolia,Phragmites australis,Canna indica）,were higher than that of the three first-generation feedstocks（FGFs）plants（Oryza sativa,Triticum aestivum,Zea mays）.Meanwhile,these three FGFs plants had higher crude fat and crude ash content.The amino acid（AAs）contents in aquatic macrophytes,including essential amino acids（EAAs）,non-essential amino acids（NEAAs）and total amino acids（TAAs）,were higher than that in the three FGFs plants.Results of flourier transfer infrared spectrum（FT-IR）characterization and fiber fractions measurement showed no difference between the contents of cellulose,hemicellulose and lignin in aquatic macrophytes（especially emergent macrophytes）and those of the three FGFs plants.Overall,due to the comparable types of fiber components but generally higher nutrient contents in the 18kinds of typical aquatic macrophytes that compared with the three FGFs plants,this study indicated that the typical aquatic macrophytes have high potential to be used for resource utilization.2.Four cellulolytic bacterial strains from Lake Donghu sediments（Wuhan,China）were isolated and characterized.The isolates（WDHS-01 to 04）represent Bacillus,Micromonospora,and Streptomyces genera.Compared with the other strains,Strain WDHS-02（Micromonospora sp.）exhibited excellent ability to decompose and utilize H.verticillata,with 54.19%degradation rate and 0.349 U·m L^–1 CMCase activity,and has the highest conversion rate of cellulose to reducing sugar.3.Seven kinds of carbon-based wetland substrate materials were prepared by aquatic plants residuals powder after degrading by screened cellulolytic bacteria and mixing with clay and mineral material.Large number of pores with different sizes were randomly distributed on the surfaces of the wetland substrate materials.Moreover,these wetland substrate materials had abundant lamella structure and relatively high surface area(S_BET).4.Microcosm constructed wetland simulation experiments were carried out to explore the effect of these wetland substrate materials on removal of pollutants in horizontal subsurface constructed wetlands（HSCWs）,and compare the differences of greenhouse gas emission rates in various wetland systems.Results presented that the addition of H.verticillata wetland substrate materials to HSCWs significantly increased the removal rates of TN,NH₄⁺-N and NO₃^--N,reduced the rate of CO₂emission,and increased the relative abundance and diversity of microorganisms in the wetland substrate.The addition of C.indica wetland substrate materials to HSCWs significantly increased the removal rates of COD,NH₄⁺-N and NO₃^--N,and significantly reduced the CO₂ emission rate compared with the wetland system added with pure gravel（controls）,and significantly reduced the CH₄ emission rate compared with the wetland system that pure C.indica powder was added（without clay and mineral material）.Moreover,the addition of C.indica wetland substrate materials to HSCWs significantly increased the relative abundance and diversity of microorganisms.In conclusion,results of my Ph D research showed that these wetland substrate materials produced in the present study can largely improve the removal efficiency of pollutants in the HSCWs,and can further reduce greenhouse gas emissions compared with the HSCWs added with pure plant powder.The outcome of this research would have significant implications for utilization and sound management of aquatic macrophytes.