As an important grain production base and the main maize-producing area in China, the black soil region in northeast China can utilize multifunctional plant growth-promoting rhizobacteria (PGPR) to convert nitrogen and phosphorus into plant-available forms through nitrogen fixation and phosphate solubilization, thereby reducing chemical fertilizer input and promoting crop growth. [Objective] To systematically screen efficient multifunctional strains from the black soil in northeast China and evaluate their effects on soil fertility and maize growth under 20% nitrogen and phosphorus reduction through low-temperature (16 ℃) germination and pot experiments, thus providing excellent strain resources for developing microbial inoculants adapted to the black soil region in northeast China. [Methods] Functional strains were isolated from rice rhizosphere soil via selective media and identified by 16S rRNA gene sequence analysis. The plant growth-promoting traits of the obtained strains, including nitrogen fixation, phosphate solubilization, and indole-3-acetic acid (IAA) production, were quantitatively determined. Furthermore, maize seed germination and pot experiments were carried out to systematically evaluate the effects of these functional strains on seed germination under low-temperature conditions (16 ℃), as well as on soil physicochemical properties and seedling growth indicators during the seedling stage, on the basis of which the potential of functional strains in improving soil quality and promoting crop growth was comprehensively evaluated. [Results] Two PGPR strains, Niveispirillum sp. YM6 and Bacillus sp. A03, were screened from rhizosphere soil and identified by 16S rRNA gene sequence analysis. Functional characterization revealed that strain YM6 exhibited both nitrogen fixation and indole-3-acetic acid (IAA) production capabilities, while strain A03 displayed both phosphate solubilization and IAA production capabilities. Under low-temperature (16 ℃) conditions, inoculation with both YM6 and A03 achieved the best performance in promoting seed germination, with a germination rate of 49.00%, a germination index 51.44% higher than the control, and shortening of 0.18 d in the average germination time, demonstrating a synergistic growth-promoting effect superior to both single-strain treatments and ternary combinations. Pot experiments further demonstrated that compared with the reduced-fertilizer control (CK-R), the ternary combination YM6+A03+ZP (Penicillium bilaiae) significantly increased the maize plant height, total biomass, total chlorophyll content, and soil available phosphorus and ammonium nitrogen by 12.73%, 82.60%, 66.30%, 29.94%, and 30.03%, respectively. Notably, the binary combination YM6+A03 showed no significant difference from the full-fertilizer control (CK-F) in these indicators but increased them by 9.08%, 63.54%, 32.81%, 21.51%, and 15.31%, respectively, compared with CK-R, outperforming all single-strain treatments. These results indicated that YM6+A03+ZP exhibited a significant synergistic enhancement effect, capable of maintaining or even improving crop productivity under chemical fertilizer reduction. [Conclusion] Single-strain inoculation exhibited limited plant growth-promoting effects. The binary combination YM6+A03 under 20% reduced fertilization maintained crop productivity comparable to that of CK-F, whereas the ternary combination YM6+A03+ZP significantly outperformed CK-F in promoting maize growth while improving black soil nutrient status, holding promise for the development of region-specific microbial inoculants adapted to the black soil region in northeast China.