Short-term legacy effects of white mustard cover cropping and tillage on arbuscular mycorrhizal fungal colonization, community composition, and abundance in volunteer barley
摘要
Brassicaceae cover crops are widely adopted in agroecosystems, yet their legacy effects on arbuscular mycorrhizal fungi (AMF) remain context-dependent and mechanistically unresolved. In this study, we assessed how a standing white mustard (Sinapis alba L.) cover crop interacts with tillage intensity to influence AMF colonization, community composition, diversity, and abundance in volunteer barley (Hordeum vulgare L.) roots. AMF responses were quantified using complementary approaches, including microscopic assessment of root colonization, 18S rRNA gene amplicon sequencing, and taxon-specific real-time PCR (qPCR). Roots were sampled before white mustard termination, thereby avoiding tissue disruption and isothiocyanate release, to distinguish host-mediated filtering from biofumigation-associated chemical disturbance. Colonization intensity was primarily determined by tillage, with significantly higher colonization under no-tillage compared to conventional tillage. Community-level responses, however, were dependent on taxonomic resolution. At the amplicon sequence variant (ASV) level, white mustard reduced AMF richness, whereas diversity and evenness were unaffected. At the genus level, richness remained stable, but diversity and evenness declined under the combined effects of cover cropping and conventional tillage, indicating that tillage modulated the impact of cover crop legacy. Dominant Glomeraceae lineages remained stable across treatments, and total AMF abundance showed no consistent response to management, although Rhizophagus irregularis was more abundant under no-tillage. Colonization intensity correlated with ASV richness rather than with individual taxa, suggesting that early symbiotic dynamics were linked to community diversity rather than to the dominance of specific lineages. These findings suggest that white mustard cover cropping, despite its well‑recognized agronomic benefits, may also carry context‑dependent shifts in AMF communities, highlighting a potential ecological trade‑off that should be considered when designing cover crop–tillage management combinations.