Distinct characteristics of the bacterial community in the rhizosphere soils of sweet potato storage roots and fibrous roots following long-term fertilization

Sweet potato (Ipomoea batatas Lam.) has two special root systems, namely, storage roots and fibrous roots. However, the response of the bacterial community characteristics in the rhizosphere soils of the two types of roots to long-term fertilization is not clear. Here, a long-term fertilization experiment was established under wheat–sweet potato crop rotation in 2011. We sampled the rhizosphere soils of storage roots and fibrous roots under three fertilization treatments (i.e., NK, no P; NPK, chemical P fertilizer; and NPKM, inorganic combined with organic fertilizers). The diversity and composition of the bacterial community and the relative abundance of specific bacterial taxa and their relationships with soil properties were investigated at the stage of sweet potato expansion. The results showed that compared to the NK treatment, the NPK treatment significantly increased soil available P (AP) in the rhizosphere of storage roots and fibrous roots by 503 % and 668 %, dissolved organic carbon (DOC) by 25 % and 18 %, and available K (AK) by 3.5 % and 12.3 %, respectively. However, compared to the NK treatment, the Chao1 index was significantly decreased under the NPK treatment in both storage roots and fibrous roots. In addition, compared to storage roots, bacterial α-diversity and soil β-glucosidase and alkaline phosphatase activities significantly improved in the rhizosphere of fibrous roots (P < 0.001) under the NPKM treatment. Chryseobacterium, Acinetobacter and Myroides were the dominant bacterial genera in the rhizosphere soil of storage roots under the NPKM treatment. Furthermore, principal coordinate analysis (PCoA) indicated that the structure of the bacterial community was markedly altered in the rhizosphere soils of storage roots and fibrous roots under the NPKM treatment. Moreover, a complex network of bacterial communities was formed in the rhizosphere of storage roots rather than that of fibrous roots. Based on redundancy analysis (RDA) and structural equation modeling (SEM), the results revealed that the diversity and structure of the bacterial community were primarily driven by the AK concentration in the rhizosphere soil of the storage roots. In summary, long-term fertilization reshaped the bacterial community in the rhizosphere soils of two types of sweet potato roots by altering the properties of the rhizosphere soils.