Multidimensional Improvement of the Soil Environment through Ryegrass-maize Intercropping and its Mechanism for Remediating Lead Contamination

Heavy metal contamination, particularly lead (Pb), poses a serious threat to global food security and soil ecological integrity. Although phytoremediation is considered an environmentally friendly approach, its efficiency remains limited due to the slow growth and low biomass of most Pb hyperaccumulator plants, especially compared with physical and chemical remediation methods. Therefore, this study aimed to investigate the potential of a ryegrass–maize intercropping system to enhance Pb remediation efficiency and improve soil environmental quality through rhizosphere microecological regulation. A pot experiment was conducted with three treatments: control (uncontaminated soil), maize monoculture, and ryegrass-maize intercropping, each with three replicates. After 120 days, soil and maize grain Pb contents, soil fertility parameters, enzyme activities, and microbial community structure were measured. Correlation analyses were performed to explore relationships among these variables. Compared with maize monoculture, the ryegrass-maize intercropping system significantly reduced soil Pb content by 82.2% and maize grain Pb content by 16.4%. Root complementarity contributed to improved soil fertility by stabilizing nitrogen, alleviating phosphorus depletion, and enhancing potassium accumulation. Intercropping also markedly increased the activities of soil enzymes associated with nitrogen cycling, particularly alkaline protease and catalase. Although Pb stress generally reduced microbial diversity, intercropping selectively enriched Pb-tolerant and bioremediation-related microbial taxa, while mitigating the suppression of sensitive phyla, resulting in a more functionally stable rhizosphere microbial community. The ryegrass-maize intercropping represents an effective strategy for remediating Pb-contaminated soils, while maintaining crop safety and improving soil ecological functions, highlighting its potential for sustainable management of contaminated farmland.