外源水杨酸对暗紫贝母连作土壤根际微生物群落及生物碱合成的调控效应

Regulatory effects of exogenous salicylic acid on rhizospheric microbial community and alkaloid biosynthesis in continuous cropping soil of Fritillaria unibracteata

摘要:

目的 针对暗紫贝母连作障碍引发的根际微环境劣化、药用品质下降问题，探究不同浓度水杨酸(salicylic acid, SA)在连作与非连作模式下的调控效应，明确缓解连作障碍的关键SA浓度及作用机制，为优化栽培技术提供理论支撑。方法 设置连作、非连作2种栽培模式及6个SA浓度梯度(0、20、50、100、200、500 μmol/L)，通过盆栽试验测定根系分泌物、土壤理化因子、土壤酶活性、生物碱含量与微生物群落结构变化，并结合相关性分析、冗余分析(redundancy analysis, RDA)解析调控机制。结果 SA对暗紫贝母根际微环境及生物碱合成的调控具有显著浓度特异性，且与栽培模式存在交互作用：根系分泌物中总酚酸在20 μmol/L和500 μmol/L SA处理下显著升高(P<0.05)，有机酸在200 μmol/L SA处理下达峰值；非连作组土壤有机碳、有机质含量显著高于连作组，50 μmol/L SA可优化土壤pH及速效磷、铵态氮供应，提升脲酶、酸性磷酸酶活性；假单胞菌门、子囊菌门为优势类群，500 μmol/L SA可富集链霉菌属等有益菌、抑制病原菌，特异性提升贝母辛、西贝母碱含量；RDA分析表明，SA通过调控根系分泌物组成重塑微生物群落，进而介导生物碱合成。结论 50 μmol/L SA为优化根际养分供应与酶活性的适宜浓度，500 μmol/L SA为有效缓解连作障碍、促进药用生物碱积累的关键浓度；SA通过“调控根系分泌物组成-重塑微生物群落结构-修复根际互作网络”的协同途径实现根际生态修复与药用品质提升，为暗紫贝母连作障碍治理提供新路径。

Abstract:

Objective To address the problems of rhizospheric microenvironment deterioration and medicinal quality decline caused by continuous cropping obstacles of Fritillaria unibracteata Hsiao et K. C. Hsia, this study explored the regulatory effects of different concentrations of salicylic acid (SA) under continuous and non-continuous cropping patterns and clarified the optimal SA concentration and underlying mechanism for alleviating continuous cropping obstacles, aiming to provide a theoretical basis for optimizing cultivation techniques.Methods A pot experiment was conducted with two cultivation patterns (continuous cropping and non-continuous cropping) and six SA concentration gradients (0, 20, 50, 100, 200, and 500 μmol/L). The changes in root exudates, soil physicochemical properties, soil enzyme activities, alkaloid content, and microbial community structure were determined. Correlation analysis and redundancy analysis (RDA) were performed to elucidate the regulation mechanism.Results SA exerted significant concentration-specific regulatory effects on the rhizospheric microenvironment and alkaloid biosynthesis of F. unibracteata, showcasing a significant interaction effect with cultivation patterns. Total phenolic acids in root exudates increased under 20 μmol/L and 500 μmol/L SA treatments (P<0.05), and organic acids reached the peak under 200 μmol/L SA treatment. The soil organic carbon and soil organic matter in the non-continuous cropping group were significantly higher than those in the continuous cropping group. SA at 50 μmol/L optimized soil pH, increased the supply of available phosphorus and ammonium nitrogen, and enhanced the activities of urease and acid phosphatase. Pseudomonadota and Ascomycota were the dominant phyla in bacterial and fungal communities, respectively. SA at 500 μmol/L enriched beneficial microorganisms such as Streptomyces, inhibited pathogens, and specifically increased the content of peimisine and sipeimine. RDA results showed that SA remodeled the microbial community by regulating the composition of root exudates, thereby mediating alkaloid biosynthesis.Conclusion SA at 50 μmol/L SA is suitable for optimizing rhizosphere nutrient supply and enzyme activities, and that at 500 μmol/L is suitable for effectively alleviating continuous cropping obstacles and promoting the accumulation of medicinal alkaloids. SA achieves rhizospheric ecological restoration and medicinal quality improvement through a synergistic pathway of regulating root exudate composition, remodeling microbial community structure, and repairing rhizospheric interaction network. This study provides a new approach for the management of continuous cropping obstacles for F. unibracteata.