| The carbon sequestration process of the coastal wetland ecosystem is one of the hot issues in the “blue carbon” research in the past 10 years.As an important part of blue carbon,the coastal mangroves,seagrass beds and salt marshes store a large amount of carbon,which has a very high carbon sequestration efficiency.As an important blue carbon pool,although mangroves only accounts for 0.4% of the offshore area,it stocks 5% of the carbon in the atmosphere.In recent years,many mangrove communities have been affected by the invasion of Spartina alterniflora,as a result,the soil carbon pool and the chemical composition and microbial community structure have changed significantly.In this study,3 transect lines were selected from inland to coastal in Zhangjiang Estuary Mangrove Nature Reserve in Fujian Province.3 plots were selected for each transect: Mangrove Community(MC),Transitional Community(TC)and S.alterniflora community(SC),3 sampling cores were selected for each plot,and 0–100 cm soil profile samples were collected in 5 layers for soil physical and chemical analysis.The physical and chemical properties,organic carbon content and microbial community structure were studied.The differences of soil organic carbon(SOC)functional groups under different vegetation types were determined by NMR spectroscopy.The results are as follows:1.Soil physical and chemical properties are significantly different in different vegetation types and soil depths.The average water content is TC>SC>MC,which decreases significantly with the increase of soil depth;the average pH value is SC>MC> TC and the average salinity was MC>TC>SC,and the salinity increased with the depth of the soil layer;the results of particle size distribution indicated that types silt were dominant at 3 vegetation,and the silt/clay content was SC>MC>TC.2.From MC to SC,the soil carbon pool was significantly reduced.The total organic carbon and particulate organic carbon content of MC were significantly higher than TC and SC,and decreased with the increase of soil profile depth.The dissolved organic carbon showed MC>SC.There is no obvious change trend with the change of soil layer.3.The organic carbon structure of each vegetation type is dominated by alkyl carbon and alkoxy carbon,followed by aromatic carbon and carbonyl carbon,and the N-alkyl carbon and phenolic carbon content is the least.The surface layer of 0–15 cm soil from MC to the SC,the content of alkyl carbon and O-alkyl carbon showed an increasing trend but was not significant.The content of aromatic carbon and phenolic carbon was significantly reduced,and the content of other organic carbon components was not significantly different.There was no significant difference in SOC composition in the deep 75–100 cm with vegetation type changes.In the 0–15 cm soil layer,the alkyl carbon/ O-alkyl carbon content is: SC > MC > TC;the aromaticity is minimum in SC,MC and TC are not significantly different;hydrophobic carbon/hydrophilic carbon is not significantly different;The aliphatic carbon/aromatic carbon showed that SC was significantly larger than the other two vegetation types,and there was no significant difference between MC and TC.In the 75–100 cm soil layer,there was no significant difference in the ratios.It indicated that the organic carbon molecular structure of S.alterniflora was simple and the degree of decomposition was higher.The organic carbon molecular structure of mangrove soil was complex and the organic carbon pool was more chemically stable.4.Under the 3 vegetation types,the OTU number and diversity index of bacteria and fungi in 0-15 cm soil layer were not significantly different,and the abundance of bacteria and fungi varied.The results of redundancy analysis indicated that different organic carbon component and functional group composition are related to the microbial composition. |
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