Structural and Predicted Functional Diversities of Bacterial Microbiome in Response to Sewage Sludge Amendment in Coastal Mudflat Soil

SIMPLE SUMMARY: Improving microbial community and functional diversity is essential for the fertility activation and development of coastal mudflat soils, an important reserve resource for sustainable agricultural development. Although sewage sludge has been proven to be an effective agricultural practice to alleviate saline sodic stress and nutrient deficiency and thereby enable coastal mudflat reclamation, knowledge regarding the structural and functional diversities of bacterial microbiome in response to sewage sludge application remains unclear. In this study, we simultaneously investigated the effects of sewage sludge amendment on physicochemical characteristics, composition, diversity, and predicted function of bacterial community in coastal mudflat soil. Results revealed that both structural and functional diversities of bacterial microbiome were significantly improved due to microhabitat modification (i.e., mitigated saline–alkali and nutrient deficiency conditions) induced by sewage sludge amendment compared to untreated soil. Additionally, bacterial groups involved in cycling processes of carbon and nitrogen were significantly enriched in sewage sludge-amended mudflat soils. The current study enhanced our understanding of mechanisms underlying microbial community and functional diversities promoted by sewage sludge amendments. ABSTRACT: The study investigated the influence of sewage sludge application at rates of 0 (CK), 30 (ST), 75 (MT), and 150 (HT) t ha(−1) to mudflats on bacterial community diversity and predicted functions using amplicon-based sequencing. Soils under sewage sludge treatments, especially the HT treatment, exhibited lower pH, salinity and higher nutrient contents (C, N, and P). Moreover, restructured bacterial communities with significantly higher diversities and distinct core and unique microbiomes were observed in all sewage sludge-amended soils as compared to the control. Specifically, core bacterial families, such as Hyphomicrobiaceae, Cytophagaceae, Pirellulaceae Microbacteriaceae, and Phyllobacteriaceae, were significantly enriched in sewage sludge-amended soils. In addition, sewage sludge amendment significantly improved predicted functional diversities of core microbiomes, with significantly higher accumulative relative abundances of functions related to carbon and nitrogen cycling processes compared to the unamended treatment. Correlation analyses showed that modified soil physicochemical properties were conducive for the improvement of diversities of bacterial communities and predicted functionalities. These outcomes demonstrated that sewage sludge amendment not only alleviated saline–sodic and nutrient deficiency conditions, but also restructured bacterial communities with higher diversities and versatile functions, which may be particularly important for the fertility formation and development of mudflat soils.