关键词: 七彩花生, 施氮, 根瘤内生菌, 化学计量特征, PICRUSt 2

Abstract: Aims The root nodules of leguminous plants are the site of biological nitrogen fixation by rhizobia, and nodules also harbor diverse endophytes, which play important roles in plant growth and nutrient status. However, how root nodule endophytes respond to nitrogen input and the associations of endophyte composition with plant ecological stoichiometric characteristics remain to be investigated. Methods Colorful peanut (Arachis hypogaea “Qicai” ) was planted in a field experiment with three levels of nitrogen treatment (N0: 0 kg N·hm–2, N1: 140 kg N·hm–2, N2: 280 kg N·hm–2 ). The structures of endophyte communities and the contents of carbon (C), nitrogen (N) and phosphorus (P) in leaves were quantified, and endophytic functions were predicted by PICRUST 2 software. Important findings The results showed that endophytes are extremely diverse, with a total of 546 families and 1?049 genera. Among them, Bradyrhizobium accounted for only 27.83% in relative abundance, and other genera accounted for more than 70%. The average proportion of Caballeronia-Paraburkholderia and Enterobacter was more than 10%. Nitrogen application decreased the diversity of endophytes and changed the community composition, and the relative abundance of some microorganisms from Bradyrhizobium, Enterobacter, Kosakonia and Pantoea increased significantly while those from Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Mesorhizobium, Mycobacterium and Burkholderia were significantly decreased. The relative abundance of the dominant genera was closely correlated with the stoichiometric characteristics of the plants. (3) The results of co-occurrence network analysis show that some modules are significantly correlated with the contents and stoichiometric characteristics of C, N, and P in the leaves. Meanwhile, the results of PICRUSt 2 functional prediction also show that the functions of microbial C, N, and P metabolic enzymes are significantly correlated with the contents and stoichiometric characteristics of C, N, and P in leaves, indicating that there is a close association of the microbial community structure with the contents and balance of plant nutrients. In summary, the results of this study show that the composition of endophytes in the root nodules of the colorful peanuts is extremely diverse, and the community structures and functions are very sensitive to nitrogen addition. In future studies, the functions of nitrogen-tolerant and sensitive endophytes can be further explored through microbial isolation and synthetic microbial community techniques.

Key words: Arachis hypogaea “Qicai”, nitrogen fertilization, root nodule endophyte, stoichiometric characteristics, PICRUSt 2