Alteration of Nutrient Substrates and Absence of Seawater Due to Coastal Embankments Affects Soil Microbial Communities in Salt Marshes of Eastern China

Abstract

Aims: Although the influence of coastal embankments on soil physicochemical properties and carbon (C) and nitrogen (N) cycling has been widely studied, the mechanisms of their effects on the soil microbial ecology are still poorly understood. Thus, the aim of this study was to investigate variations in 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 embankments on the bacterial and archaeal communities of the invasive Spartina alterniflora Loisel., as well as native Suaeda salsa (L.) Pall. and Phragmites australis (Cav.) Trin. ex Steud. saltmarshes in the coastal China.Results: Embankments significantly decreased the Simpson diversity index of the S. alterniflora saltmarsh, while increasing the OTU richness in the P. australis saltmarsh. Additionally, the bacterial and archaeal community compositions in the embanked S. alterniflora and P. australis saltmarshes were considerably modified. However, no variations were found between the bacterial and archaeal communities of the natural and embanked S. salsa saltmarshes.Conclusions: These results were possibly because embankments decreased the soil nutrient substrates (e.g., soil organic C and N) dramatically in the S. alterniflora saltmarsh, while increased soil nutrient substrates significantly in the P. australis saltmarsh. However, embankments had a negligible effect on the soil nutrient substrates in the S. salsa saltmarsh. Moreover, embankments increased the abundance of Betaproteobacteria, and decreased the abundance of sulfur- and sodium-dependent bacteria due to the dramatic change in soil physicochemical properties.

Increasing coastal reclamation by Invasive alien plants and coastal armoring threatens the ecological sustainability of coastal wetlands

“…Reclamation by invasive alien plants and embankment seawalls has seriously harmed the coastal ecosystem's structure and function in sequestering carbon, absorbing waves and storms, reducing water pollution, and enabling breeding habitats for flora and fauna (Feng et al, 2021;Feng et al, 2022). The introduction of embankment seawalls in invasive S. alterniflora-dominated salt marshes significantly altered the GHG regulation capacity of coastal marshes.…”

“…Since S. alterniflora was labeled as an invasive plant in the early 2000s and now covers ~50,000 ha of China's coastal wetlands, seawalls have increasingly been constructed to control its invasion and spread. Previous research primarily documented the adverse effects of S. alterniflora invasion (Meng et al, 2020) and seawall expansion (Feng et al, 2021;Li et al, 2021). However, both positive and adverse aspects are assessed concerning S. alterniflora invasion and expansion of coastal embankments.…”

Effect of Seawall Embankment Reclamation on the Distribution of Cr, Cu, Pb and Zn Pollution in Invasive Spartina alterniflora and Native Phragmites australis Coastal Saltmarshes of East China

“…Although coastal embankment enhanced flora growth, it negatively impacted subsurface saline water extraction [28], whereas reduced soil salinity accompanying coastal embankments was the main driver of changes in plant and soil nitrogen pools [29]. Due to coastal embankments, soil microbial ecosystems are altered by nutrient substrates modification and the lack of seawater [30], whereas copper phytoavailability is facilitated by luminous soluble organic materials in coastal wetlands altered by coastal embankment [31]. However, in mangrove forests, the impacts of embankments on wrack composition and dynamics may be lower than on unvegetated coastlines [32].…”