Indigenous rhizosphere growth-promoting bacterial strains in the Erhai Lake Basin: isolation, identification, and evaluation of the application potential in the grain-economy collaboration model

Abstract:

Background Exploring indigenous microorganisms for innovative research and development of green investment brands is an important way to boost agricultural development in plateau watersheds.Objective To excavate the indigenous plant growth-promoting rhizobacteria (PGPR) in the Erhai Lake Basin and evaluate their plant growth-promoting properties, thus providing strain resources for the development of microbial agents.Methods A total of 12 vegetable soil samples were collected from 3 major grain and vegetable planting towns in the Haixi area of the Erhai Lake Basin. The dilution coating method, functional culture medium screening, physiological and biochemical property tests, and 16S rRNA gene sequencing, and strain-seedling potting, and soil enzyme activity measurement were conducted to isolate and identify the strains and evaluate their plant growth-promoting properties.Results A total of 28 bacterial strains with plant growth-promoting functions such as nitrogen fixation, phosphorus solubilization, siderophore production, and indole-3-acetic acid (IAA) secretion were isolated from the soil of vegetable fields in the Erhai Lake Basin. Among them, six strains with better performance were identified, belonging to Bacillus, Alcaligenes, Providencia, and Myroides. The six strains could solubilize organic phosphorus, solubilize inorganic phosphorus, and produce IAA within the ranges of 41.16–158.63, 190.84–280.50, and 15.03–186.24 mg/L, respectively. In the pot experiments with seedlings of maize and asparagus lettuce, representative crops of grain-economy collaboration, inoculation with the isolated strains significantly promoted the growth and development of the aboveground and underground parts of the seedlings. Specifically, the inoculation averagely increased the plant height and total root length of maize seedlings by 31.80% and 58.96%, respectively. Meanwhile, it averagely increased the plant height and root fresh weight of asparagus lettuce seedlings by 41.47% and 83.87%, respectively. Moreover, the application of the isolated strains activated mineral elements in the soil to varying degrees and significantly improved the activities of some soil enzyme activities compared with the blank treatment.Conclusion In the Erhai Lake Basin with limited application of chemical fertilizer and weak research and development of local bio-organic fertilizer, the six strains of PGPR screened from vegetable fields in this study can be used as strain resources for the development of local indigenous microbial inoculants. The strains demonstrate great application potential in promoting the growth and development of maize and asparagus lettuce, improving the soil nutrient utilization efficiency and soil enzyme activity, and reducing exogenous nutrient input.