老参地土壤自毒物质及病原菌的积累特征及轮作后的变化规律

American ginseng (Panax quinquefolium L.) was cultivated with serious continuous cropping obstacles, extremely restricted its sustainable development. Autotoxins and pathogens accumulated in American ginseng continuous cropping soil were important factors to cause the continuous cropping obstacles. Therefore, the accumulation and variation of autotoxins and pathogens were the key factors to influence their effect. This project is performed to study on the accumulated process of pathogens and autotoxins such as phenolic compounds and fatty acids, and the effects of plant growth status and soil environment on them during American ginseng growth season. Moreover, by establishing LC-MS and GC-MS method, the variation characteristic of autotoxins will be analyzed and metabolic profiling will be clarified in American ginseng continuous cropping soil after 1-5 years of wheat/maize rotation cropping. And the effect of autotoxin metabolite will be evaluated through bioassay. In addition, in order to elucidate the variation discipline of pathogens under rotation cropping, 5-7 American ginseng root disease pathogens will be qualitatively and quantitatively analyzed through molecular techniques such as T-RFLP and RT-PCR technology. On the basis of above works, replanted American ginseng growth and quality will be determined after rotation on through pot experiment, to verify the improved effect of rotation cropping on American ginseng continuous cropping soil. The results from this research will further enrich the theoretical study of continuous cropping obstacles, and provide scientific supports to establish appropriate rotation cropping scheme on American ginseng continuous cropping soil.

西洋参在栽培过程中存在严重的连作障碍问题，严重制约了其可持续发展。种植西洋参后老参地自毒物质和病原菌积累是导致连障碍的重要原因，而自毒物质和病原菌在土壤中的积累量及变化是决定其作用强弱的关键因子。本项目拟对西洋参生长过程中分泌至土壤中酚酸、脂肪酸等自毒物质和病原菌的积累过程，及其受植物生长状态和土壤环境的影响进行系统研究。通过建立LC-MS/GC-MS分析技术，研究轮作小麦/玉米1-5年后老参地土壤自毒物质的变化特征，明确自毒物质的代谢谱；并通过生物测定对代谢产物的自毒作用进行评价。此外，分别采用T-RFLP/RT-PCR技术，对5-7种西洋参主要病害病原菌在土壤中的变化进行定性定量分析，明确轮作后的变化规律。在上述研究基础上，结合盆栽实验测定轮作土壤中种植西洋参的生长和质量指标，初步验证轮作对老参地土壤的改良作用。研究结果进一步丰富连作障碍理论，也为老参地建立合理的轮作体系提供科学依据。

西洋参在栽培过程中存在严重的连作障碍问题，严重制约了其可持续发展，种植西洋参后老参地自毒物质和病原菌积累是导致连障碍的重要原因。本项目对西洋参生长过程中分泌至土壤中自毒酚酸和病原菌的积累过程，及其受植物生长状态和土壤环境的影响进行分析，系统研究了玉米轮作消减老参地土壤连作障碍的效果及机制。（1）通过分析不同生长年限西洋参种植土壤中自毒酚酸和病原菌的季节变化规律，发现1-4年生西洋参根际的主要酚酸p-香豆酸、总酚酸在同一季节含量接近，不同季节中夏季微生物数量最高，而酚酸浓度最低。西洋参发生根腐病、疫病后根际土壤中9种酚酸的含量无显著改变。（2）采用HPLC检测土壤中7种酚酸含量，发现老参地土壤中p-香豆酸、水杨酸、阿魏酸、丁香酸与总酚酸显著高于玉米地，轮作1年后显著下降。首次建立了土壤中5种脂肪酸类自毒物质的GC-MS检测方法，发现老参地土壤中硬脂酸、棕榈酸的含量显著高于玉米地。但在各土壤浓度下它们对西洋参种胚生长的抑制强度没有差异，推论其在老参地中的富集可能并不是引起连作障碍的主要原因。（3）采用末端限制性片段长度多态性(T-RFLP)技术建立了18属30种西洋参相关真菌的TRF数据库，对土壤真菌区系进行分析发现真菌优势度(D)与均匀度指数(J)在老参地中为最低，轮作5年后有所恢复。建立了土壤中2种重要病原菌的real-time PCR定量检测体系，发现与老参地相比，轮作1年后土壤中灰葡萄孢菌Botrytis cinerea的数量显著降低。（4）通过对土壤肥力的系统分析，明确了老参地中速效养分显著高于玉米地，轮作3年后显著降低。（5）以轮作不同年限土壤再植西洋参的生长及病害发生情况为依据，通过多元线性回归分析，明确了土壤微生物多样性及病原数量两个因子是老参地土壤自毒的关键因子，老参地的轮作年限应为3年以上。项目成果揭示了玉米轮作对老参地土壤改良的作用机制，建立的西洋参-玉米-西洋参轮作体系有较好的应用效果及前景。