Differential Effects of Organic Ameliorants on the Reassembly of Bacterial Communities in Newly Amended Coastal Mudflat Salt-Affected Soil

Abstract

Understanding the influences of organic ameliorants amendment on the soil microbiome is fundamental for the alleviation of environmental constraints in coastal mudflat salt-affected soils. However, how the compositional and structural diversity of the microbial community responds to different organic inputs, and key environmental determinants and relevant mechanisms driving soil microbiome reassembly in coastal agroecosystems have not been illustrated. In this study, field experiments were conducted to investigate the effectiveness and underlying mechanisms of sewage sludge (S) and sludge-based vermicompost (V) at different application amounts (0, 50, 100, and 200 t ha−1) on variations in the compositional and structural diversities of soil bacterial community in coastal mudflats. The underlying driving factors, including soil physicochemical and enzymatic properties, were determined to estimate their effects on soil bacterial community. Results show that both types and amounts of organic ameliorants exerted significant influence on the alterations of bacterial community diversities. Particularly, restructured bacterial communities with significantly higher bacterial populations, lower Shannon diversities, and distinct core and unique community profiles were observed in organic ameliorant-amended soils as compared to CK. The co-occurrence networks of bacterial core OTUs reveal that V exhibited more profound effects than those of S on the scale and interactions enhancement and stability reduction of soil bacterial guilds. Additionally, both S and V significantly alleviated environmental constraints with lower pH and salinity, but higher soil organic carbon (SOC) amounts and enzyme activities were observed in the amended soils. Moreover, the effects of S and V on soil amendment were enhanced with the increase in the application amounts of organic ameliorants. Redundancy analysis (RDA) reveals that environmental factors (e.g., pH, salinity, SOC, sucrase, urease, and phosphatase) were pivotal determinants, accounting for 78.05% of the total bacterial community variations in coastal salt-affected soils across different treatments.