Soil microbial variability in contrasting grown flue-cured tobacco under long-term continuous cropping

Soil microbial communities are directly impacted by agricultural management practices and play a crucial role in determining crop productivity. Therefore, we investigated how long-term continuous cropping would impact the composition of microbial communities and their feedback to flue-cured tobacco. We selected flue-cured tobacco with contrasting agronomic traits from three fields under continuous cultivation for over a decade, where well-grown plants had 1.45, 1.28, 1.17 and 1.25 times greater height, leaf number, length and width than poorly grown tobacco, respectively. The root zone soils of flue-cured tobacco with contrasting agronomic traits were collected to analyse the community structure and network characteristics of soil bacteria and fungi. Although bacterial and fungal diversity, dominated by stochastic processes, remained invariant between contrasting agronomic traits, community composition differed significantly at the order level. Specifically, the well-grown tobacco was enriched with Micrococcales, Xanthomonadales and Eurotiales groups known for their role in organic matter degradation. In contrast, poorly grown tobacco was uniquely enriched with bacteria typically involved in nitrate cycling, such as Nitrospira, Nocardioides and Betaproteobacteria. Bacterial function prediction based on Tax4Fun2 showed that functions related to amino acid cycling were enriched in the root zone of well-grown tobacco. Additionally, the rhizosphere of well-grown tobacco exhibited a more complex bacterial network with larger network hubs than that of poorly grown tobacco. In conclusion, the enrichment of organic matter decomposers and nitrate transformers in the root zones of continuously cropped flue-cured tobacco significantly impacts agronomic traits, with a complex soil bacterial network and key network hubs playing a crucial role in maintaining tobacco growth.