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Aims: Although the influences of coastal embankments on soil physicochemical properties and carbon (C) and nitrogen (N) cycling have been widely reported, the mechanisms of their effects on soil microbial ecologies remain poorly understood. Thus, the aim of this study was to investigate the variations in the diversity and composition of soil bacterial and archaeal communities between natural and embanked saltmarshes, as well as the determinants that drive these variations. Methods: 16S rRNA gene sequence analysis was performed to assess the impacts of coastal embankments on the bacterial and archaeal communities of native Suaeda salsa, Phragmites australis, and invasive Spartina alterniflora saltmarshes on the east coast of China. Results: Embankments were found to significantly decrease the microbial diversity of S. alterniflora salt marsh, while increased the OTU richness of P. australis salt marsh. Embankments modified the compositions of soil bacterial and archaeal communities in both S. alterniflora and P. australis salt marshes. However, variations in the microbial diversity, richness, and community compositions between the native and embanked S. salsa salt marshes were insignificant. Conclusions: These results were possibly because the embankment significantly altered soil nutrient substrate levels (e.g., soil organic C and N) by variations in plant residues and soil physiochemical properties in S. alterniflora and P. australis saltmarshes, whereas the embankment had no observable changes in the soil nutrient substrate and plant residue in S. salsa saltmarsh. This study also elucidated the effects of coastal embankments on biogeochemical cycles, and highlighted their potential hazards to ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Soil fungal communities play a critical role in ecosystem carbon (C) and nitrogen (N) cycling. Although the effect of plant invasions on ecosystem C and N cycling is well established, its impact on soil fungal communities is not fully understood. The objective of this study was therefore to understand the variations in soil fungal communities as affected by plant invasion, and the mechanisms that drive these changes. Methods: We examined the impacts of invasive Spartina alternifolia Loisel. (SA) on soil fungal abundance, diversity, community composition, trophic modes and functional groups in comparison with bare flat (BF) and native Suaeda salsa (Linn.) Pall. (SS), Scirpus mariqueter Tang et Wang (SM), and Phragmites australis (Cav.) Trin. ex Steud. (PA) communities in coastal salt marshes of eastern China, based on analyses of the quantitative polymerase chain reaction (qPCR) and Illumina MiSeq DNA sequences of fungal internal transcribed spacer (ITS) region. Results: SA invasion increased the soil fungal abundance and diversity compared to BF, SS, SM, and PA soils. The increased soil fungal abundance and diversity were highly related to soil organic carbon (C) and nitrogen (N), water-soluble organic carbon (WSOC), litter C:N ratio, and root C:N ratio. Soil fungal community composition was shifted following SA invasion. Specifically, SA invasion significantly enhanced the relative abundance of Basidiomycota, and reduced the relative abundance of Ascomycota compared with BF, SS, SM, and PA soils. Additionally, SA invasion changed soil fungal trophic modes and functional groups. The relative abundance of saprotrophic fungi significantly increased, while the relative abundances of symbiotic and pathotrophic fungi decreased following SA invasion. Conclusions: Our data revealed that SA invasion altered soil fungal abundance, diversity, community composition, trophic modes and functional groups, which were primarily driven by the quality and quantity of plant residues, soil nutrition substrates, as well as soil physicochemical properties. The changes in soil fungal communities, especially their trophic modes and functional groups following SA invasion would greatly affect soil C and N decomposition and accumulation with potential feedback on climate change. [ABSTRACT FROM AUTHOR]

The impacts of coastal embankments on nitrogen (N) dynamics are of great importance in salt marshes. However, effects of embankments on seasonal N dynamics in the plant-soil systems of Suaeda salsa salt marshes are still not well understood. Therefore, the edaphic moisture and salinity, biomass, N concentrations and storage in different plant tissues; the extent of organic and inorganic N subpools in soil subsystems; as well as N immobilization and mineralization by microorganisms in embanked and neighboring natural S. salsa salt marshes through all four seasons were investigated in Yancheng, Eastern China. Our results revealed that embankments increased the biomass and N storage of dead tissues (e.g., litter), while they decreased the biomass and N storage of live tissues (e.g., living aboveground tissues and roots) of S. salsa through decreased edaphic moisture and salinity. Furthermore, under the influence of embankments edaphic water-dissolvable N, e.g.,edaphic dissolved organic N (EDON) and nitrate and nitrite N (TNN), significantly increased with higher N inputs from S. salsa litter. This water-dissolvable N was an important source of N for plants, which translated to higher N concentrations in live plant tissues. However, this excess absorbed N appeared not to facilitate the growth of plants, which would ultimately return to the soil from plant residues. Our results suggested that the decreased edaphic soil moisture and salinity due to embankments had negative impacts on the biomass and N storage of S. salsa plant tissues, which were likely due to shifts in the edaphic osmotic potential. Subsequently, a cascading butterfly effect may be initiated due to the impaired growth of S. salsa , to which more attention should be paid. This study represents a step forward by providing valuable insights and an improved elucidation of the seasonal plant-soil N dynamics of S. salsa salt marshes. • The embankment reduced the N storage of living plant tissues by decreasing the edaphic moisture and salinity. • Increased litter N storage due to the decreasing edaphic moisture and salinity by the embankments. • Enhancing N inputs from litter by the embankment lead to the edaphic water-dissolvable N remarkably increased. • The increased N concentrations of microbes and plants caused by lowering edaphic moisture and salinity due to the embankments. [ABSTRACT FROM AUTHOR]