Partitioned nitrogen fertilisation in peanut rhizosphere and geocarposphere drives specific variation soil microbiomes

Peanut is a plant characterised by belowground fruiting that absorbs nutrients not only through its roots but also through its pods. However, little is currently known regarding the species of bacteria that contribute to nutrient absorption and utilisation in this plant's pod and root zones. This study examined the effects of root and pod area nitrogen (N) fertiliser application on peanut rhizosphere and geocarposphere microbial communities and functions. Using two peanut cultivars [nodulated Huayu 22 (H) and non-nodulated NN-1 (B)], we applied the following four treatments: no N fertiliser (HT1, BH1); N applied to geocarposphere soil (HT2, BT2); N applied to rhizosphere soil (HT3, BT3), and N applied to both rhizosphere and geocarposphere soil (HT4, BT4). The results revealed that compared with HT1 and BT1, the HT3, HT4, BT3, and BT4 treatments promoted increases in total plant accumulated N of 11.2, 30.1, 38.5, and 9.9%, respectively. Moreover, N input contributed to an increase in the abundance of bacteria colonising the surrounding pods, which differed significantly from bacteria colonising the rhizosphere. Among the top four bacterial phyla detected, we recorded a significant increase in the relative abundances of Proteobacteria and Gemmatimonadetes in response to treatments HT2 and HT4, whereas the highest relative abundances of Acidobacteria and Actinobacteria were detected in HT3 plants. Regarding cultivar B, we detected increases in the relative abundances of Bacteroidetes and Gemmatimonadetes in response to the BT2 and BT4 treatments, and in the relative abundance of Actinobacteria in BT3 treated soil. The findings of FAPROTAX functional analysis revealed clear differences among the T2, T4, and T3 treatments of two peanut cultivars concerning the functional groups with the highest relative abundances. These findings will make a considerable contribution to enhancing our understanding of the effects of N fertilisation on soil microbial structure and function in the rhizosphere and geocarposphere of peanuts and can provide a basis for identifying beneficial bacteria for promoting N utilisation and yield enhancement.