Multi-Trait Screening Identifies Cold-Adapted Soybean Rhizobia from Northeastern China as Candidate Inoculant Strains

Area of Science:

• Agricultural Microbiology
• Plant-Microbe Interactions
• Soil Science

Background:

• Effective rhizobial inoculants are crucial for sustainable soybean production in high-latitude environments.
• Indigenous rhizobia require adaptation to local soil conditions and abiotic stress tolerance for symbiotic nitrogen fixation.

Purpose of the Study:

• To characterize phenotypic diversity, stress tolerance, symbiotic nitrogen fixation, and plant growth-promoting rhizobacteria (PGPR) traits of indigenous rhizobial strains.
• To identify superior rhizobial strains for developing effective biofertilizers for cold-region soybean agriculture.

Main Methods:

• Isolation and characterization of 66 indigenous rhizobial strains from four ecological regions in Heilongjiang Province, China.
• Assessment of carbon/nitrogen source utilization, physiological properties, and tolerance to salinity, pH, temperature, and drought.
• Hierarchical cluster analysis for phenotypic differentiation and evaluation of symbiotic performance and PGPR activity in eight representative strains.

Main Results:

• Habitat-associated phenotypic differentiation was observed, with stress-tolerance traits being the most significant variation.
• Northwest Arid Sandy Region isolates exhibited the broadest stress tolerance, while Sanjiang Plain isolates showed conservative profiles.
• Strains SN1 and SN8 from the Songnen Plain demonstrated the highest symbiotic performance, and strain FS1 showed high ACC deaminase activity.

Conclusions:

• A multi-trait evaluation framework integrating symbiotic and non-symbiotic traits is effective for screening rhizobia.
• Strains SN1 and SN8 are identified as the most promising candidates for field validation as inoculants in cold-region soybean agriculture.
• This approach supports the development of region-specific biofertilizers for sustainable soybean cultivation.