Mechanistic insights into yield enhancement of Chimonobambusa opienensis bamboo shoots driven by organic fertilizer combined with Azotobacter Chroococcum via soil nutrient-microbe-metabolite interactions

Chimonobambusa opienensis is a bamboo shoot species with considerable ecological and economic value; however, its low yield constrains large-scale cultivation. Bio-organic fertilizers, which are sustainable alternatives to chemical fertilizers, can improve soil conditions and enhance productivity. However, the mechanisms by which they increase yield through soil nutrient-mediated regulation of microbe-metabolite interactions in C. opienensis remain unclear. We conducted a two-year field trial with five fertilization treatments: organic fertilizer (OF), Azotobacter chroococcum (Ac), Bacillus amyloliquefaciens (Ba), organic fertilizer combined with (A) chroococcum (OF + Ac), and organic fertilizer combined with (B) amyloliquefaciens (OF + Ba). Amplicon sequencing and liquid chromatography-mass spectrometry were employed to assess the soil microbial composition and metabolic activity across treatments. The results demonstrated that soil chemical properties were the key drivers of microbial community structure. Co-occurrence network analysis revealed that microbial networks in the OF + Ac group were simpler and less interconnected than those in other treatments. Non-targeted metabolomics identified 133 soil metabolites. The control group was significantly enriched in fatty acyl compounds, whereas carbon- and nitrogen-containing metabolites were markedly increased in Ac and OF + Ac treatments. Moreover, the addition of A. chroococcum (in Ac and OF + Ac treatments) induced the most pronounced shifts in microbial community composition. Network analysis of microbial ASV-metabolite associations showed that nearly all differential ASVs responded specifically to either Ac or OF + Ac treatment. Furthermore, the network connector Bradyrhizobium (ASV2748) responded exclusively to OF + Ac and exhibited significant positive correlations with numerous nitrogen-containing metabolites. Structural equation modeling proposes a model that soil nutrients were the primary drivers of microbial community changes and directly enhanced bamboo shoot yield. This study proposes a model in which the OF + Ac enhances (C) opienensis bamboo shoot yield without compromising palatability, through a soil nutrient-microbe-metabolite pathway supported by SEM results, whereas Ba also increases yield but at the expense of palatability. These findings offer new insights into the interaction mechanisms among C. opienensi, soil microbiota, and metabolites.