Macrogenomic analysis of the previous crops effects on tobacco soil microbiomes

Crop rotation serves as a valuable agronomic practice for addressing succession barriers in crops, particularly in tobacco growing. The effect of different previous crops on the microbiology of soils planted with tobacco is an area that deserves further study.This study investigated the chemical properties, microbial community composition, and functional genes related to nutrient cycling in tobacco-planted soils with no preceding crop (CK), garlic (T1), or faba bean (T2) as preceding crops. The results indicated that the T1 treatment significantly decreased the contents of soil organic matter (SOM, 11.32%), total phosphorus (TP, 29.41%), total potassium (TK, 3.33%), and available potassium (AK, 46.88%), whereas the T2 treatment notably increased the content of hydrolyzable nitrogen (HN, 34.88%). Furthermore, the T2 treatment significantly enhanced the diversity of soil bacteria and fungi, particularly the bacterial Shannon index (1.49%) and fungal Chao1 (24.11%) and Shannon (7.73%) indices. In terms of microbial composition, compared to the CK, the T2 treatment enriched the relative abundance of beneficial bacterial genera (e.g., Sphingomonas, Methyloceanibacter, Rhizophagus) and reduced the relative abundance of pathogenic fungi (e.g., Fusarium). Additionally, T2 treatment increased the abundance of functional genes associated with nitrogen, phosphorus, and potassium, thereby promoting the cycling of soil nutrients. Overall, faba bean as a preceding crop was more beneficial for subsequent tobacco cultivation than fallow periods or garlic.