Regulatory mechanism of phosphorus supply intensity on the plant nitrogen acquisition in soybean: Insight from the differences of rhizobia diversity between high-oil soybean and non-high-oil soybean

Phosphorus supply plays a critical role in regulating symbiotic nitrogen acquisition in soybeans, yet the mechanisms underlying varietal differences between high-oil and non-high-oil varieties remain poorly understood. This study investigated the varietal-specific mechanisms of phosphorus supply intensity on plant nitrogen acquisition via rhizobial community restructuring using two high-oil (Kenong 18, Kenong 39) and two non-high-oil varieties (Heihe 43, Longken 310) under five phosphorus levels (0, 35, 70, 105, 140 kg·hm ^− 2 ). The results showed that high-oil varieties exhibited superior growth performance and nitrogen acquisition efficiency at 105 kg·hm ^− 2 phosphorus supply, with increases of 19.99% in plant height, 4.13% in shoot dry weight and 17.96% in root dry weight versus controls. Nodule number, dry weight and haemoglobin content increased by 83%, 30% and 33.02%, respectively, in high-oil genotypes. Enhanced nitrogen metabolism was evidenced by significantly elevated GOGAT/GS activities (9.32–17.13%) and leaf total nitrogen content. Crucially, under optimal phosphorus conditions, high-oil varieties enriched specific nitrogen-fixing rhizobia, such as Bradyrhizobium sp. 173_3_ module and Rhizobium sp ., and exhibited stronger correlations between community structure and soil available phosphorus (RS-AP), along with a predicted greater potential for nitrogen acquisition and aerobic chemoheterotrophy. This study demonstrates that optimal phosphorus supply enhances symbiotic nitrogen acquisition efficiency in high-oil soybeans by driving the assembly of more specialized rhizobial communities, providing microbial mechanistic insights for varietal-specific phosphorus management in soybean cultivation.