Abstract:

【Objective】In China's wheat-maize production region, the Huang-Huai-Hai Plain primarily employs a winter wheat-summer maize rotation cropping system. Sandy loam soil, widely distributed in the Huang-Huai-Hai region, demonstrates various properties and associated challenges, including poor structural integrity, and weak water retention and nutrient-holding capabilities. To improve fertilizer utilization, enhance soil fertility, optimize crop yields, and improve quality, we identified a multi-functional plant growth-promoting rhizobacteria（PGPR）and validated its broad-spectrum growth-promoting effects within this rotation system. 【Method】From the sandy loam soil within the maize rhizosphere, we isolated a multi-functional PGPR bacterium and evaluated its ability of producing indole-3-acetic acid（IAA）, organic phosphorus solubilization, and potassium release ability. We identified the bacterium at the species level using morphological, physiological, biochemical, and 16S rDNA sequence analysis. Under shaken culture conditions, we determined the optimal conditions for IAA production by PGPR YM3. Subsequently, we assessed its growth-promoting ability through maize pot experiments. We verified its broad-spectrum yield-increasing effects in a field trial within the winter wheat-summer maize rotation system. 【Result】1）a multi-functional root-associated growth-promoting bacterium named YM3 was isolated, identified as Bacillus subtilis, and found to produce 59.21 mg/L IAA, solubilizing 0.72 mg/L organic phosphoruing, and releasing 18.56 mg/L potassium. The optimal conditions for IAA production by YM3 were achieved when using maltose and peptone as carbon and nitrogen sources, respectively, within a pH range of 6-8 and a liquid volume of 25 mL/250 mL. 2）Maize pot experiments revealed that soil IAA, available phosphorus, and available potassium levels significantly increased by 75.00%, 48.66%, and 20.00%, respectively, compared to soils treated with heat-inactivated YM3 bacterial suspension. Maize seedlings exhibited substantial improvements in root length, root surface area, root volume, root tip number, and root branch number, by 67.95%, 59.21%, 51.13%, 71.34%, and 92.06%, respectively. Additionally, maize plants had significant increases in fresh weight, plant height, relative chlorophyll content, total nitrogen, total phosphorus, and total potassium, with enhancements of 39.86%, 23.51%, 18.27%, 17.68%, 52.26%, and 36.53%, respectively. 3）Field trials within the winter wheat-summer maize rotation system demonstrated that soil available nitrogen, available phosphorus, and available potassium levels significantly increased by 9.08%, 13.78%, and 16.66%, respectively, with a yield increase rate of 42.18% upon YM3 bacterium agent application. Maize field soil showed notable increments of 19.18% and 15.95% in available phosphorus and available potassium, respectively, with a yield increase rate of 13.22%. 【Conclusion】The isolated B. subtilis strain YM3, possessing the ability to produce IAA, solubilize organic phosphorus, and release potassium, demonstrates strong adaptability and broad-spectrum growth-promoting effects in sandy loam soil of the Huang-Huai-Hai Plain. Moreover, it enhances soil fertility and elevates yields within the winter wheat-summer maize rotation system.

Key words: plant growth-promoting rhizobacteria, IAA, solubilizing organic phosphorus and release potassium, wheat-maize rotation, crop yield