Maize/soybean intercropping improves soil macroaggregation and phosphorus dynamics: the role of root functional traits and phoC-harboring bacteria

• Maize/soybean intercropping effects on rhizosphere soil aggregation and phosphorus dynamics are soybean genotype-dependent. • Intercropping-induced increases in macroaggregates are associated with increased soybean fine root length (0.2–1 mm). • Intercropping altered acid phosphatase activity and phoC gene composition in macroaggregates. Maize/soybean intercropping holds great potential for enhancing soil aggregation and phosphorus (P) cycling, yet the rhizosphere mechanisms underlying aggregate formation and microbial regulation of P dynamics at the aggregate scale remain poorly understood. This study aimed to examine how intercropping-induced changes in root functional traits influence aggregate formation, and how phoC -harboring bacteria mediate P pools and acid phosphatase activity at the aggregate scale. In a pot experiment using acidic soil, two soybean genotypes differing in root traits (YC with an average 20% smaller diameter and 25% higher specific root length than EX) were intercropped with maize. Intercropping increased P uptake in both soybean genotypes but had no significant effect on maize. At the rhizosphere scale, intercropping increased large macroaggregates (>2 mm) fraction by 47% in YC but not in EX, with corresponding increases of 105% and 41% in maize intercropped with YC and EX, respectively. The greater macroaggregation in YC was associated with increased fine root (0.2–1 mm) length, rhizosheath organic C, and rhizosphere Gram-negative bacteria and actinomycetes biomass. At the aggregate scale, intercropping enhanced citrate- and HCl-extractable P in large macroaggregates and reduced CaCl 2 -extractable P in microaggregates in YC, whereas EX showed depletion of HCl-extractable P in large macroaggregates and microaggregates. Intercropping also significantly increased acid phosphatase activity in macroaggregates and phoC -harboring Cupriavidus across all aggregates in YC, with no significant changes in these two indicators in EX. Overall, soybean genotype regulates how intercropping shapes rhizosphere aggregation and associated P dynamics, highlighting the importance of genotype selection for enhancing P cycling in intercropping systems.