Introduction In long-term straw-returning systems, a year-scale understanding of how contrasting tillage practices shape soil fungal succession and community assembly remains limited. Methods Based on a long-term field experiment, we investigated soil fungal communities using ITS sequencing during years 3–7 after straw return (2020–2024) under farmer shallow rotary tillage (CK) and three treatments: deep ploughing return (DPR), subsoiling straw return (SSR), and no-tillage mulching return (NTR). Fungal diversity, community composition, functional guilds, and assembly pathways were evaluated by integrating functional guild assignment, co-occurrence network analysis, and null-model metrics (βNTI) with a neutral community model. Results Fungal α -diversity showed a pronounced mid-term increase (years 4–5; +18–40% in Shannon index) and stabilized thereafter (variation 15%), indicating a transition toward community equilibrium. Community composition exhibited directional turnover, with Ascomycota decreasing (~31–44%) and Basidiomycota increasing (up to ~226–228%). By year 7, clear treatment-specific differences emerged: Ascomycota was higher in DPR than in SSR (+62.96%), whereas Blastocladiomycota increased markedly in NTR (4.49–31.40-fold). At the genus level, DPR enriched Trichosporiella (up to 29.74-fold higher than NTR), while Solicoccozyma was more abundant in SSR and NTR (2.94–3.00-fold higher than DPR). Functionally, DPR increased symbiotic guilds (+90.81%), whereas SSR and NTR showed higher pathogen-associated guilds (e.g., SSR 1.63-fold higher than DPR). Network analysis revealed that NTR formed the largest network but with stronger pathogen-associated signals, whereas DPR showed higher cooperativity (93.61% positive edges) and stability. Assembly analyses indicated overall stochastic dominance, with increased deterministic processes in NTR in year 5 (βNTI 2). The neutral model showed moderate fit (R 2 = 0.5132), with greater deviation under NTR. Soil microbial biomass, enzyme activities, soil organic matter, and moisture were key drivers of community shifts. Discussion These results demonstrate that contrasting straw-returning practices regulate fungal succession through compositional turnover, functional differentiation, and assembly reconfiguration, providing insights for optimizing straw-return management and promoting sustainable cropland systems.
Liu et al. (Tue,) studied this question.