| The carbon cycle of coastal wetlands plays an important role in the global carbon cycle,and the iron cycle plays an important role in the preservation of organic carbon.In order to explore the impact of Spartina alterniflora invasion on the carbon binding characteristics of coastal wetlands,in this study,a total of 10 sampling sites were selected from 8 areas including Minjiangkou,Jiulongjiangkou,Yueqing Bay,Zhangjiangkou,Zhanjiang,Beihai,Hengsha and Chongming Island in China's five provinces and cities such as Guangxi,Guangdong,Fujian,Zhejiang and Shanghai.We collected soil of0?10cm in Kandelia candel,Avicennia marina and Phragmites australis wetlands before and after Spartina alterniflora invasion in coastal wetlands,and analyzed the changes in iron valence composition,composition of iron-bound organic carbon the occurrence form of iron oxide,iron-bound organic carbon,the community structure and distribution characteristics of iron-reducing bacteria and iron-oxidizing bacteria after Spartina alterniflora invaded indigenous plants in coastal wetland.The results are as follows:1.The invasion of Spartina alterniflora into coastal wetlands can change the iron valence state(Fe(?),Fe(?))in the 0?10 cm soil of the wetland.The content of Fe(?)and Fe(?)in Kandelia candel wetland,Avicennia marina wetland,Phragmites australis wetland and Spartina alterniflora invaded wetland ranged from 1.06?1.73 mg·g-1and7.67?21.83 mg·g-1,0.71?2.49 mg·g-1 and 0.77?21.79 mg·g-1,2.34?2.76 mg·g-1 and6.84?18.08 mg·g-1,0.96?6.31 mg·g-1 and 0.59?32.70 mg·g-1.In general,after Spartina alterniflora invaded the Kandelia candel wetland and Avicennia marina wetland(except the Avicennia marina wetland in Zhangjiangkou),the soil Fe(?)content increased,especially in Minjiangkou and Jiulongjiangkou Kandelia candel wetland Fe(?)content increased significantly(P<0.05).Except for Chongming Island,after Spartina alterniflora invaded the reed wetland,the Fe(?)content decreased significantly(p<0.05).2.The content of three iron oxides(Fed,Feo,Fep)in the wetland of Kandelia candel and Spartina alterniflora were 23.94 mg·g-1,6.51 mg·g-1,0.64 mg·g-1 and 21.75 mg·g-1,6.45 mg·g-1,0.59 mg·g-1;the content of Fed,Feo,and Fep in Avicennia marina and Spartina alterniflora wetland soil were 15.59 mg·g-1,3.85 mg·g-1,0.78 mg·g-1 and 15.97mg·g-1,3.66 mg·g-1,0.74 mg·g-1;the content of Fed,Feo,and Fep in Phragmites australis and Spartina alterniflora wetland soil were 21.35 mg·g-1,6.39 mg·g-1,0.85 mg·g-1 and20.92 mg·g-1,6.96 mg·g-1,0.80 mg·g-1.In general,the content of Fed and Fep decreased after Spartina alterniflora invasion,but the difference of Feo content was not significant.3.After Spartina alterniflora invaded Kandelia candel,Avicennia marina,and Phragmites australis wetland,the average soil iron oxide-bound organic carbon(Fe-OC)content decreased by 22.91%,42.25%and 22.53%respectively.Among them,after Spartina alterniflora invaded the Jiulongjiangkou Kandelia candel wetland,Zhangjiangkou Kandelia candel wetland,Beihai Avicennia marina wetland,and Hengsha Phragmites australis wetland,the soil Fe-OC ratio decreased significantly(p<0.05).After invading the Kandelia candel wetland in Yueqing Bay and the Avicennia marina wetland in Zhanjiangkou,the proportion of soil Fe-OC decreased significantly(p<0.05).On the overall level,soil Fe-OC decreased after Spartina alterniflora invaded coastal wetlands.The 10 typical coastal wetlands in this study,Fe-OC is mainly formed through the adsorption pathway,while the co-precipitation pathway has relatively little contribution.And after the invasion of Spartina alterniflora,the Fe:OC in the soil has a tendency to decrease,indicating that the invasion of Spartina alterniflora makes the binding pathway of iron oxide to organic carbon in wetland soil more inclined to adsorption.4.It can be seen from the alpha diversity index that the invasion of Spartina alterniflora increased the diversity of soil iron-reducing bacteria in the Avicennia marina wetland and Phragmites australis wetland,and decreased the diversity of soil iron-reducing bacteria in the Kandelia candel wetland.The invasion also caused the succession of the dominant genus of iron-reducing bacteria in the wetland soil.After the invasion of Spartina alterniflora,the abundance of the dominant genus Desulfuromonas in the Kandelia candel wetland was significantly reduced and became a non-dominant genus.The abundance of Anaeromyxobacter was significantly increased and became the third dominant genus;the abundance of Bacteroides was significantly reduced after the invasion of Spartina alterniflora in the wetland of Avicennia marina and became a non-dominant genus.After Spartina alterniflora invaded the Avicennia marina wetland,the relative abundance of Bacteroidetes iron-reducing bacteria was significantly reduced,and the relative abundance of Proteobacteria iron-reducing bacteria was significantly increased(p<0.05).Environmental factors and carbon components can affect the relative abundance of iron-reducing bacteria in wetland soils.The relative abundance of Geobacter was significantly negatively correlated with soluble organic carbon,soil microbial biomass carbon,and p H(p<0.01),and the relative abundance of Halothiobacillus was significantly positively correlated with soil total organic carbon(SOC)(p<0.05),and significantly negatively correlated with soil microbial biomass carbon(MBC)(p<0.05).5.The number of soil iron-reducing bacteria and iron-oxidizing bacteria in coastal wetlands respond differently to the invasion of Spartina alterniflora.After the invasion of the Kandelia candel wetland in Minjiangkou,the number of soil iron-reducing bacteria in0?10 cm soil increased significantly(p<0.05),and there was no significant change in the number of iron-reducing bacteria in the 0?10 cm soil of the Avicennia marina wetland in zhangjiangkou and the Phragmites australis wetland in Minjiangkou.The number of soil iron-oxidizing bacteria increased significantly after invading the Kandelia candel wetland and Phragmites australis wetland in Minjiangkou(p<0.05);the number of soil iron-oxidizing bacteria decreased significantly after invading the Avicennia marina wetland in Zhangjiangkou(p<0.05).6.The invasion of Spartina alterniflora decreased the diversity of oxidizing bacteria in the wetland of Kandelia candel,and increased the diversity of iron-oxidizing bacteria in the Avicennia marina wetland and Phragmites australis wetland.The relative abundance of Proteobacteria iron-oxidizing bacteria was significantly increased(p<0.05),and the relative abundance of Desulfobacterota iron-oxidizing bacteria was significantly reduced(p<0.05).In addition,after the invasion of Spartina,the abundance of Geobacter iron-oxidizing bacteria in the Kandelia candel wetland was significantly reduced and became a non-dominant genus,while the abundance of Sediminibacterium was significantly increased and became the third dominant genus.After Spartina alterniflora invaded the reed wetland,the abundance of Gallionella increased significantly and became the dominant genus.Environmental factors and carbon components can affect the relative abundance of iron-oxidizing bacteria in wetland soil.The relative abundance of Pseudomonas has a extremely significant positive correlation with salinity(p<0.01),and a extremely significant negative correlation with Labile organic carbon(LOC)(p<0.01),the relative abundance of Acidobacterium was significantly positively correlated with soil dissolved organic carbon(DOC)(p<0.05),and the relative abundance of ariprofundus was extremely significantly positively correlated with soil salinity(p<0.01)and SOC and LOC showed a significant negative correlation(p<0.05). |
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