Soil Microbial Community Of Mangrove Forests And Its Responses To The Invasion Of Spartina Alterniflora In The Minjiang River Estuary

In plant-soil ecosystems,the rhizosphere is well-known as a dynamic interface for the interactions of plant roots,soil and microbes.The root-associated microbial community that promotes energy flow,information transmission,and nutrient cycling is vital for plant health and growth.With the deep understanding of the importance of underground processes,the study of the influence of invasive plants on soil microbial diversity,physical and chemical properties and ecosystem functions has become a hot issue in the field of invasive ecology in recent years.In the coupling relationship between the invasion of exotic plants and the changes of structure and function of soil ecosystem,the feedback relationship between the structure and function of microbial community in soil and aboveground plants can reveal the invasion mechanism of exotic plants and provide scientific basis for the protection and restoration of invasive ecosystems of exotic plants.This study adopted Biolog,PLFA,High-throughput sequencing technologies with the goal of the community metabolic activity and function diversity,community structure,abundance of the microbial community rhizospheric soil collected from three vegetation communities.These three communities included monocultures of both mangrove?MC?and S.alterniflora?SC?as well as a third community,the Mangrove-S.alterniflora?MS?ecotone community within the Minjiang River Estuary Wetland in Fujian Province,South China.The results showed that:?1?The SOC,TN,TP,TK and enzyme activities in rhizospheric soils of three different vegetation communities were in the order of MC>MS>SC.The results revealed that S.alterniflora invasion resulted in a significant decline of rhizospheric nutrients.The soil physical-chemical properties were positively correlated with enzyme activities,among them,Suc,CAT were significantly or extremely significant correlated with TN and SOC,while Ure,PHO were significantly or extremely significant correlated with TN,TP,and TK.?2?In the total 31 single carbon substrates,the utilization rate of carbon source of rhizospheric soil microbial community of the vegetation community increased with time,but there was obvious difference in S curve,the order of size was SC>MC>MS.The utilization rate of carboxylic acids,polymers and carbohydrates by microbes in rhizospheric soil is higher than that in phenolic acids,amino acids and amines.The invasion of S.alterniflora will affect the metabolic activity of microorganisms in the rhizosphere of mangroves,which will lead to the decrease of the functional diversity index of microbial communities.Principal component analysis?PCA?identified 2 principal component factors in relation to carbon sources,explaining 67.32%and 26.1%of the variation,respectively.Carboxylic acids,polymers,carbohydrates were the three main carbon sources separating the 2 principal component factors.The correlation between the functional diversity index of soil microbial community and the soil physical and chemical properties and enzyme activities were positively correlated.The Simpson index were significantly or extremely significantly correlated with TN,TP,TK,Ure;the Shannon-wiener index and the Brillouin index were significantly or extremely significant correlated with pH;the McIntosh were significantly or extremely significant correlated with SOC?TN?Suc?CAT?Ure.The results showed that the difference of functional diversity of biological communities was one of the important reasons for the difference of soil nutrient content.?3?There were 22 PLFAs that were significantly different in rhizospheric soil from three different vegetation communities,there were 20,21,19 PLFAs in MC,SC,MS,respectively.The MS soil exhibited richer PLFAs than the other vegetation types.The PLFAs biomarkers of three species with the highest contents were 16:0,16:1w7c,9Me15:0w,and 18:1w12c.There was a significant difference in the relative biomass of soil microbial biomass.Bacteria exhibited the richest distribution,followed by fungus,actinomycetes,and protozoans.Community diversity indices showed a similar pattern,MS soil microbial community diversity indexes were less than those of MC.The soil microbial community diversity indexes decreased following the invasion of S.alterniflora.Principal component analysis was able to distinguish the characteristics of microbial communities in different vegetation communities and identified 2 principal component factors in relation to microbial community diversity,explaining 63.58%and 29.61%of the variation,respectively.The soil physic-chemical properties were closely correlated with enzyme activities,and SOC,TN,sucrose,and catalase were significantly correlated with the PLFAs of gram-positive bacteria and actinomycetes.?4?On the basis of high-throughput sequencing results,the rhizospheric soil microbes of the cultivated communities can be classified into 56 phylums,109 classes,199 orders,347 families,543 genera.The dominated bacterial groups observed in all samples at the phyla level:Proteobacteria,Firmicutes,Nitrospirae,Bacteroidetes.The sum of relative abundance can be 70.54-76.74%.The relative abundance of Proteobacteria subgroups in different rhizospheric soil samples showed that five subgroups of Proteobacteria,listed from most to least common,were Alphaproteobacteria,Gammaproteobacteria,Betaproteobacteria,Deltaproteobacteria,Epsilonproteobacteria.In MC,the major genera of rhizospheric soil,listed from most to least common,were Desulfatiglans,Helicobacter,Desulfovibrio,and Haliangium.In MS,Acidiferrobacter,Ignavibactrium,Vogesella,Tolumonas and Hydrogenophaga were the major genera,listed from most to least common.Serratia,Methanosaeta,Desulfobulbus,Spirochaeta₂,Candidatus Nitrosopumilus,Lactobacillus,Caldithrix,Marinicella,Sulfuricurvm,Desulfatiglans,listed from most to least common,were significantly predominant in SC.we found obvious differences in the bacterial communities of mangrove,the mangrove-S.alterniflora ecotone and S.alterniflora rhizospheric soil based on the analysis of the relative abundance of the bacterial communities at different taxonomic levels.The richness of bacteria in rhizosphere soil of mangrove community decreased and the community structure changed after the invasion of S.alterniflora.Both the correlation and redundancy analyses suggested that the soil nutrient content was the main soil factor affecting the relative abundance of bacterial communities,and the soil nutrients play an important role in the shifts of soil bacterial community diversity.