The Effects Of Plants On Carbon Storage And The Relationship Between Carbon And Nitrogen In The Sediments Of River Wetlands And Constructed Wetlands

When people vigorously developed industrial activities,a large number of greenhouse gases were emitted into the atmosphere,which led to greenhouse effect.Greenhouse effect caused global climate change,which resulted in irreversible damage to the whole earth ecosystem.Wetland is an important carbon pool in terrestrial ecosystems.The plants in wetland which have a high level of net primary productivity can absorb part of the carbon dioxide from the atmosphere and convert it into organic matter to store in wetland sediments,thus mitigating the impacts of climate change.The carbon storage of sediments accounts for more than 90%of the total carbon storage in wetlands.Carbon accumulation in sediments of wetland depends on the balance between carbon input and carbon output.Plants directly input organic carbon into wetlands through litter decomposition and root exudates.Microbial mineralization and respiration are the main ways of carbon output in wetland ecosystems,and plants can indirectly affect the organic carbon storage of sediments through the effects on microbial activities.The research on the influence mechanism of plants on carbon storage and the relationship between carbon and nitrogen in the sediments of river wetlands and constructed wetlands is helpful to deepen the understanding of carbon storage function in the sediments of wetland ecosystems.This research has a guidance meaning for the scientific management of wetlands,and has an important contribution on using the carbon storage function of wetlands to mitigate global climate change.In order to understand the carbon storage function of sediments in constructed wetlands,two main types of constructed wetlands(surface flow and subsurface flow constructed wetlands)were selected as the research objects.The storage and composition of sediment organic carbon(SOC)in surface flow constructed wetlands and subsurface flow constructed wetlands of Zhaoniu River and Daotun Catchment in Shandong Province were compared.This study analyzed the relationships of carbon storage with physicochemical properties,plant biomass,and microbial community in the surface flow constructed wetlands and subsurface flow constructed wetlands to explore the mechanism of carbon storage in constructed wetlands.This study verified the important effects of plants on carbon storage and the relationship between carbon and nitrogen in wetland sediments.Then,Xinxue River Wetland and Xinxue River constructed wetland in Nansi Lake Basin of Shandong Province were selected as the research sites.The invasive plant Alternanthera philoxeroides(Mart.)Griseb.was taken as an example to determine the content and density of SOC in the sediments in the sites with plant invasion and non-invasion.The effects of plants on SOC in the river wetlands and constructed wetlands were analyzd from the perspective of sediment physicochemical properties and microbial community.After that,sediment samples in four seasons in the sites with and with no plant in Xinxue River Wetland and Xinxue River Constructed Wetland were collected.The content and composition of SOC and the relationship between carbon and nitrogen in four seasons in the sites with and with no plant were analyzed.Combined with 16S rRNA high-throughput sequencing and PICRUSt function prediction,the influence mechanism of plants on carbon storage and carbon-nitrogen relations in wetland sediments was further analyzed from the perspective of microbial community structure and functional composition.In order to explore the direct impact of plants,this study simulated the effects of water level and water quality changes caused by global changes on the carbon-nitrogen relationships in the decomposition process of plant litter under laboratory conditions.The results showed that the carbon and nitrogen storage per unit volume in the sediments of the subsurface flow constructed wetlands were significantly higher than those in the sediments of surface flow constructed wetlands.The significant difference of SOC in surface flow constructed wetlands and subsurface constructed wetlands was mainly the different composition of SOC.In the surface flow constructed wetlands,HFOC accounted for more than 95%of SOC,while HFOC in subsurface flow constructed wetlands only accounted for only about 34.6%?50.8%of SOC.In the surface flow constructed wetlands and subsurface flow constructed wetlands,total nitrogen(TN)and SOC-related microorganisms had significant effects on the composition of SOC.In addition,plant biomass in the surface flow constructed wetlands limited the light fraction organic carbon(LFOC)and affected the composition of SOC in the sediments.In the subsurface flow constructed wetlands,SOC was not limited by the higher plant biomass.Plants also make the coupling relationship between carbon and nitrogen in the sediments of subsurface flow constructed wetlands closer than that of surface flow constructed wetlands.The limitation of plants on the carbon storage and carbon-nitrogen relationship in the sediments of surface flow constructed wetlands was an important reason for the difference between the two types of constructed wetlands.In the river wetland and constructed wetland,the carbon storage of wetland sediments with plant cover was higher than that of wetland sediments without plant.In the river wetland,dissolved oxygen explains 20.5%of the variation of microbial community structure.The decrease of dissolved oxygen caused by invasive plants affected the microbial community in the river wetland,thus affecting carbon storage in sediments.Sediment temperature and pH explained 15.6%and 19.8%of the total variation of bacterial community structure in the constructed wetlands,respectively.Invasive plants led to the decrease of sediment temperature and the variations of microbial community structure,which further affected the carbon storage in the constructed wetland sediments.The indicator species with significant difference between invasive and non-invasive sites specifically showed the effects of invasive plants on microbial community by changing dissolved oxygen and sediment temperature.In the two types of wetlands,plants changed the physicochemical properties of the sediments and affected the microbial community of the sediments,thus affecting the carbon storage in the sediments.Plants and seasons had significant effects on the content of SOC and each fractions organic carbon in the constructed wetland,but only affected the content of DOC in the sediments of the river wetland.The different effects of plants and seasons on SOC in the constructed wetland and river wetland were attributed to the different responses of microbial community structure and function to plants and seasons.In the river wetland,plants increased the microbial function related to amino acid metabolism through the influence on sediment moisture content,which increased the consuming of DOC content in river wetland sediments.The function of carbohydrate metabolism in the river wetland in summer was significantly higher than that in other seasons,which consumed the organic matter input from photosynthesis of plants.This could explain that seasons have no significant impacts on the SOC in the river wetland.Compared with the river wetland,constructed wetlands have more stable microbial communities and are easier to fix organic carbon from plant sources.The increase of water level and nutrient enrichment caused by global change significantly affected the decomposition and nutrient dynamics of plant litter.Litter carbon(C)concentration was the main factor controlling litter decomposition.Carbon concentration,phosphorous(P)concentration,and stoichiometric characteristics of litter decomposition were the controlling factors of nutrient release.The change of C concentration caused by nutrient enrichment and water level change affected the decomposition process and nutrient dynamics of litter.There was a positive linear correlation between C release and nitrogen(N)release.The N concentration and P concentration of litter could explain 26.6%of the change in C release/N release.The concentrations of N and P in the decomposing litter regulated the coupling relationship between C release and N release.This research studied the effects of plants on the relationship between carbon and nitrogen in wetlands from the coupling relationship of C and N in the process of litter decomposition,and pointed out the important effects of limiting elements N,P in plant l itter on the relationship between carbon and nitrogen in wetlands.In summary,this study revealed the influence mechanisms of plant on the carbon storage and the relationship between carbon and nitrogen in sediments of the river wetland and the constructed wetland from the aspects of physicochemical properties,microbial community structure and functional composition,and plant litter decomposition.It is found that plants directly influenced the carbon storage and carbon-nitrogen relationship in sediments of the constructed wetlands through plant biomass.Plant also affected the carbon storage of the river wetland and constructed wetland by changing the physicochemical properties of sediments and affecting microbial community.Plants indirectly impacted carbon storage and carbon-nitrogen relationship in the river wetlands and constructed wetlands by affecting microbial community structure and functional composition.The carbon-nitrogen coupling of plant litter showed a strong evidence for the carbon-nitrogen coupling relationship in wetland sediments.There were significant differences in carbon storage and carbon-nitrogen relationship between the constructed wetland and river wetland.Compared with river wetlands,constructed wetlands have higher carbon sequestration potential.This study is of great significance to understand the carbon storage function of wetland ecosystem and also provides a basis for the scientific management of wetland..