Integrated rhizosphere bacterial community and root exudate analysis clarify the key bacteria in enhancing Pyrus betulifolia saline-alkali stress tolerance

Root-associated microbiota play a crucial role in the response of plants to environmental stress. Pyrus betulifolia is a wild pear species with strong saline-alkali resistance. However, it remains unclear whether the rhizosphere bacteria of P. betulifolia contribute to its saline-alkali response and which specific bacteria are key players in this process. In this study, we focused on the saline-alkali tolerance of ‘Qingzhen V111’ (P. betulifolia) and demonstrated its robust saline-alkali resistance and the significance of rhizosphere microbes in this process. We conducted 16S rRNA gene amplicon sequencing and metabolomic analysis of the rhizosphere soil and root exudates from P. betulifolia ‘Qingzhen V111’ and P. ussuriensis ‘QAUP-1′, which exhibit differing levels of saline-alkali tolerance. The results indicated that the rhizosphere bacterial communities of ‘Qingzhen V111’ and ‘QAUP-1′ displayed markedly different responses to saline-alkali treatment. We then screened various bacterial genera associated with the ‘Qingzhen V111’ genotype and identified marker genera that respond to saline-alkali treatment in the rhizosphere of ‘Qingzhen V111’. Through a metabolomic analysis of root exudates, we identified genotype-dependent differential root exudates and P. betulifolia specific saline-alkali responding root exudates. Through correlation analysis between the aforementioned rhizosphere bacteria and root exudates, as well as soil incubation experiments, we verified that Variovorax and Bacillus are genotype dependent bacteria predominantly recruited in the rhizosphere of ‘Qingzhen V111’ via root exudates. Furthermore, under saline-alkali stress treatment, ‘Qingzhen V111’ recruits increased populations of Nitratifractor and Novosphingopyxis through its root exudates. Notably, we isolated Variovorax paradoxus N6 and Bacillus cereus BN7, which were confirmed to enhance the saline-alkali tolerance of both Arabidopsis and ‘Qingzhen V111’ through promoting the growth and Catalase (CAT) activities of plants. These findings have significant implications for enhancing the adaptability of Pyrus plants to saline-alkali stress in the context of plant–microbe interactions.