Synergies of wheat competitive superiority and safflower rhizosphere microbiome-mediated nutrient acquisition drive high profitability in wheat-safflower intercropping systems

Rational intercropping optimizes cropping systems and boosts land productivity in resource-constrained regions. Unlike cereal–legume intercropping relying on rhizobial N fixation, mechanisms of high-yield non-leguminous wheat–safflower intercropping remain unclear. Two intercropping patterns (2W1S: 2-row wheat / 1-row safflower; 3W3S: 3-row wheat / 3-row safflower) and corresponding monoculture controls were established to explore interspecific competition, crop yield, economic benefits, and microbe-mediated nutrient uptake processes. Results showed wheat had a strong competitive advantage in nutrient acquisition, with increased N and P uptake, while safflower uptake was suppressed. The 3W3S pattern was identified as the optimal configuration by balancing interspecific competition: it maintained a 24.91% yield increase in wheat compared with monoculture, while reducing safflower corolla yield loss to only 0.48% (far lower than 5.00% in 2W1S), and increased net economic return by 16.35% relative to 2W1S. Both intercropping patterns achieved land-use advantages (Land equivalent ratio > 1). Intercropping exerted minor effects on the wheat rhizosphere but strongly regulated safflower rhizosphere processes: soil available nutrients decreased by 5.27%–25.47%, microbial biomass carbon and nitrogen increased by 11.74% and 9.47%, urease and sucrase activities rose by 9.30% and 77.67%, and the relative abundance of core functional microbes was substantially enriched (MND1: +24.46%; Cladosporium: +95.89%; arbuscular mycorrhizal fungal taxa: +93.36%). Partial least squares path modeling confirmed that these microbes enhanced carboxylic acid metabolism (+85.27%) and amino acid metabolism (+64.42%), thereby accelerating nutrient cycling and improving nutrient use efficiency to alleviate safflower yield loss. Unlike N-fixing cereal–legume systems, this study reveals a dual synergistic mechanism in non-leguminous wheat–safflower intercropping: wheat gains yield via competitive resource capture, while safflower mitigates yield loss through microbe-mediated nutrient compensation. The 3W3S pattern optimizes interspecific competition to maximize both productivity and economic benefits. These findings provide a scientific foundation for sustainable, high-efficiency cropping systems in resource-constrained regions of the North China Plain.