Nutrient Storage And Microbial Community In Soils Of The Newly Created Tidal Marsh In The Yellow River Estuary

Estuarine marsh,as an important"source","sink"and"converter"of biogenic elements,plays a major role in maintaining regional ecological security.The Yellow River estuary is the best-preserved,expansive and youngest estuarine marsh ecosystem in the warm temperate zone of China.Affected by the runoff and sediment discharge,the newly created tidal marsh in the Yellow River estuary silting or erosion frequently,resulting in dynamic changes in the soil nutrient pool of it,which affects the stability of the ecosystem.The newly created tidal marsh in the Yellow River estuary become a"natural experimental site"for current study on marsh ecological processes,especially marsh biogeochemical processes,with its instability and fragility.The Suaeda salsa marsh and the Tamarix chinensis marsh are the most widely distributed marsh types in the newly created tidal marsh of the Yellow River estuary.However,there are few comparative research on variations of nutrient fractions（N,P,S）and microbial community structure and diversity in soils.In this paper,to explore the distributions and stocks of different nutrients forms,microbial community structure and diversity in marsh soils,and ecological stoichiometric characteristics of soil nutrients in different marshes,the Suaeda salsa marsh and Tamarix chinensis marsh in newly created tidal marsh of the Yellow River estuary were investigated.Based on field sampling,laboratory experiments and Illumina Miseq high-throughput sequencing technology,the key influencing factors affecting nutrient storage and microbial community structure in marsh soils were identified,and the relationship between nutrient forms and microbial communities in marsh soils were revealed preliminary.The main results were as follows:i)The contents of nutrients in the soils of the newly created tidal flat in the Yellow River estuary were at a medium level as a whole,except that the content of TS(804.96～881.50 mg·kg^-1)which was slightly higher than the world average soil sulfur content(700 mg·kg^-1),the content of TN(519.47～1035.84 mg·kg^-1)and TP(470.10～533.55 mg·kg^-1)were lower than the average nitrogen content in marsh soils in China(1100 mg·kg^-1)and the average phosphorus content of Chinese soils(500mg·kg^-1).ii)The contents of TP or TS in the soil of the Suaeda salsa marsh and the Tamarix chinensis marsh were similar,which was mainly related to the similarity of the soil parent material and pedogenic environment in the research area.However,the contents of TN in the soil of the Suaeda salsa marsh was 1.24 times that of the Tamarix chinensis marsh,which may be related to the difference in soil nitrogen mineralization and nutrient return from residual decomposition between the two.The distribution of plant roots and soil physical-chemical properties in different marshs may have profound effects on the distribution of nutrients in different forms.In terms of the contents of inorganic nutrients in both marshs soil showed as follows:NH₄⁺-N>NO₃^--N,IP>Ca-P>Fe/Al-P,TIS>H₂O-S>Adsorbed-S>HCl-Soluble-S>HCl-V olatile-S.iii)Although the stocks of TN or TP in the soils of the newly created tidal flat in the Yellow River estuary were at high levels,the proportion of effective nitrogen and phosphorus nutrients（mineral-N and Fe/Al-P）is extremely low,indicating that the soils in the research area are limited by nitrogen and phosphorus nutrients.In contrast,the stocks of TS and TIS were at high levels and C/S<200,suggesting that sulfur may not be the limiting nutrient in the area.iv)There were some similarities as well as differences in the compositions of soil microbial community between the Suaeda salsa marsh and the Tamarix chinensis marsh.Proteobacteria was the common dominant phylum of microorganisms in soils of the two marshes with the relative abundance of 47.30～61.05%,followed by Bacteroidetes and Chloroflexi.There were 12 common genus and 16 endemic genus in both marsh soils,among which the predominant genus in the Suaeda salsa marsh was Acinetobacter（2.43～24.28%）,while that in the Tamarix chinensis marsh was unidentified＿Enterobacteriaceae（2.76～33.27%）.The Shannon and Chao indexes showed that the richness of microbial flora in soil of the Tamarix chinensis marsh was much higher than that in the Suaeda salsa marsh.The structure and diversit y of microbial communit y in soils of the Suaeda salsa marsh were mainly affected by soil nutrients（N,P,S）and p H,while the structure and diversit y of microbial communit y in soils of the Tamarix chinensis marsh were also influenced by soil bulk density,EC and soil grain composition.In recent years,the amount of exogenous n utrients（especially NH₄⁺-N）imported into the Yellow River estuary always maintained a high level,the microbial diversit y in the Suaeda salsa marsh soils may be more sensitive to exogenous nutrients input than in the Tamarix chinensis marsh.v)The mean values of C/N,C/P and C/S in the soil layers of 0～60 cm in the Suaeda salsa marsh were lower than those in the Tamarix chinensis marsh,while N/P,N/S and P/S were the opposite,mainly due to differences in the physical-chemical properties and nutrient contents in the soils of the different marshs.Soil grain composition,nutrient contents and ecological stoichiometric ratios are the main controlling factors for soil nutrient storage,and microorganisms may also indirectly influence nutrient storage through use of nutrients selectively.In addition,differences in the distribution of plant roots and nutrient supply relationships between aboveground and belowground parts may also effect absorption and utilization of inorganic nutrients in soil by plants,thereby affecting the storage characteristics of nutrients in soil.This paper found that,although the contents of nutrients in the soils of the newly created tidal flat in the Yellow River estuary were at a medium level as a whole,the supply of mineral nitrogen and effective phosphorus were very limited.In recent years,the amount of exogenous nitrogen and phosphorus（nutrient input,nitrogen and wet-dry deposition,etc）imported into the Yellow River estuary always maintained a high level,the response of the Suaeda salsa marsh to exogenous nutrients input may be more sensitive than that of the Tamarix chinensis marsh.