Vegetation-Driven Changes in Soil Salinity Ions and Microbial Communities Across Tidal Flat Reclamation

Abstract

Soil microbes play a vital role in tidal flat ecosystems but are highly susceptible to disturbances from land reclamation. This study investigated the dynamics of bacterial communities and their environmental drivers across a 50-year reclamation chronosequence under three vegetation types (bare flats, reed beds, and rice fields). The results showed that, after 50 years of reclamation, total dissolved salts decreased significantly in vegetated zones, particularly in rice fields, where Cl^- dropped by 54.71% and nutrients (SOC, TN, TP) increased substantially. Key ions, including HCO₃^-, Cl^-, and K⁺, were the primary drivers of microbial community structure, exerting more influence than total salinity (TDS) or pH. Bacterial abundance and diversity increased over time, with rice fields showing the highest values after 50 years. Actinobacteriota and Proteobacteria were positively correlated with HCO₃^- and K⁺, while Cl^- negatively affected Acidobacteriota. Genus-level analyses revealed that specific taxa, such as Sphingomonas and Gaiella, exhibited ion responses diverging from broader phylum-level patterns, exemplifying niche-specific adaptations to salinity regimes. These findings underscore the pivotal role of vegetation type and individual salinity ions in driving microbial succession during tidal flat reclamation. A phased vegetation strategy, starting with reed colonization and followed by rice cultivation, can enhance soil quality and microbial diversity. This research provides important insights for optimizing vegetation management and ion monitoring in sustainable tidal flat reclamation.

Keywords: reclamation stage; salinity ions; soil bacterial community; tidal flat; vegetation cover type.

Figure 1

Geographic locations of the study area and sampling sites. yr1, yr3, yr5, yr10, and yr50 denote 1, 3, 5, 10, and 50 years after reclamation, respectively.

Figure 2

Variations in Pearson correlation coefficients among soil parameters: K⁺ (a), Na⁺ (b), Ca²⁺ (c), Mg²⁺ (d), Cl⁻ (e), HCO₃⁻ (f), SO₄²⁻ (g), pH (h), SOC (i), and TDS across different vegetation cover types. GT: bare flat; LW: reed bed; SD: rice field.

Figure 3

Principal coordinates analysis (PCoA) of soil bacterial communities at the ASV level across reclamation years (yr1, yr3, yr5, yr10, and yr50) in tidal flats. (a) Bare flat; (b) reed bed; (c) rice field.

Figure 4

Community composition of soil bacterial phyla in tidal flats across different reclamation years (1, 3, 5, 10, and 50) and vegetation cover types. (a) Bare tidal flat; (b) Reed bed; (c) Rice field. Taxa with relative abundances < 0.01 are grouped as “others”.

Figure 5

Variations in (a) bacterial Shannon diversity index and (b) gene copy numbers in tidal flat soils across different reclamation years (1, 3, 5, 10, and 50) and vegetation cover types. GT: bare tidal flat; LW: reed bed; SD: rice field.

Figure 6

Redundancy analysis (RDA) of soil bacterial communities at the phylum level in relation to selected environmental variables. (a) Correlation between soil salinity ion composition and bacterial community structure. (b) Correlation between major soil chemical properties and bacterial community structure. Colored points represent samples from different reclamation years (1, 3, 5, 10, and 50). Grey arrows indicate species, while red arrows indicate environmental variables.

Figure 7

Spearman correlation heatmaps between environmental factors (X-axis) and the top ten bacterial taxa (Y-axis) at two taxonomic levels: (a) Phylum; (b) Genus. Color gradients represent correlation coefficients (R values), with red and blue indicating positive and negative correlations, respectively. Clustering dendrograms for taxa and environmental factors are shown on the left and top. Significance levels: * 0.01 < p < 0.05; ** 0.001 < p < 0.01; *** p < 0.001.