Trade‐off between soil bacterial network complexity and stability: Depth‐dependent effects of tillage practice and cropping system

Abstract Soil microbial network complexity and stability are fundamental to ecosystem functioning, yet their interdependence across agricultural practices remains poorly understood. This study investigates long‐term (>10 years) tillage (no‐tillage NT vs. conventional tillage CT) and cropping systems (maize ( Zea mays L.)–soybean ( Glycine max Merr.) rotation MS vs. continuous maize MM) effects on bacterial network complexity and stability across soil layers (0–5 cm and 5–20 cm) in the black soils of northeastern China. High‐throughput sequencing and cohesion‐based network analysis were used to assess microbial interactions, complexity as the sum of absolute cohesion values, and stability as the ratio of negative to positive cohesion. Results revealed depth‐dependent trade‐offs between bacterial network complexity and stability. Compared to CT, NT increased complexity at 0–5 cm (2.13%) but reduced it at 5–20 cm (−2.69%), where stability improved (2.20%). Compared to MM, MS decreased complexity at both depths (0–5 cm: −2.11%; 5–20 cm: −3.94%) and improved stability at 5–20 cm (1.84%). Maximum complexity occurred under NTMM (no‐tillage with continuous maize cropping) (0–5 cm) and CTMM (conventional tillage with continuous maize cropping) (5–20 cm), whereas stability was greatest under NTMS (no‐tillage with maize–soybean rotation) (5–20 cm). A significant negative correlation between complexity and stability was detected at both depths ( r = −0.38 at 0–5 cm; r = −0.75 at 5–20 cm), supporting the “complexity–stability paradox” in soil ecosystems. These findings underscore that trade‐offs between microbial network complexity and stability are shaped by the interaction of agricultural practices and soil depth. Tailoring tillage and crop rotation strategies to influence specific soil depth zones is crucial for enhancing microbial resilience and sustaining long‐term soil health.