马铃薯连作栽培对土壤微生物多样性的影响

Effect of potato continuous cropping on genetic diversity of soil microorganisms

  • 摘要: 马铃薯是宁夏回族自治区南部山区重要的粮菜兼用作物, 随栽培面积持续扩大, 轮作倒茬困难, 由此带来的连作障碍问题日渐突出。为探明马铃薯连作障碍机制, 分别采集马铃薯正茬、连作1年、6年和10年的根际土壤样本, 利用末端标记限制性片段长度多态性(terminal restriction fragment length polymorphism, T-RFLP)技术研究连作栽培对根际土壤微生物多样性的影响, 以期揭示马铃薯根际土壤主要菌群动态变化规律及连作障碍的可能原因。结果表明: 连作栽培后马铃薯土壤细菌和真菌DNA仍具有较高的T-RFLP多态性, 但不同连作年限根际土壤中优势T-RFs片段发生变化, 多年连作使某些T-RFs消失; 随连作年限增加, 根际土细菌Shannon-Wienen指数、Simpson指数和Sorenson指数下降, 而真菌Shannon-Wienen指数和Simpson指数上升。菌群分析发现, 土壤细菌中以厚壁菌门(Firmicutes)芽孢杆菌纲(Bacilli)和梭菌纲(Clostridia)所占比例最大。连作使细菌和真菌菌群发生变化, 芽孢杆菌纲、鞘氨醇纲(Sphingobacteria)等比例下降甚至消失, β-变形菌纲(Beta proteobacteria)和异常球菌纲(Deinococci)比例上升; 土壤真菌中座囊菌纲(Dothideomycetes)煤炱目(Capnodiales)随连作年限增加比例下降, 粪壳菌纲(Sordariomycetes)肉座菌目(Hypocreales)随连作年限增加比例上升。马铃薯连作使根际土壤中芽孢杆菌属(Bacillus)等有益菌属的细菌减少, 罗尔斯通菌属(Ralstonia)等致病菌属的细菌增加。连作导致马铃薯根际土壤细菌多样性水平降低, 真菌多样性水平升高, 根际土壤微生物多样性存在明显差异, 连作破坏了根际土壤微生物群落的平衡, 使其根际土壤微生态环境恶化。连作障碍可能是多因素综合互作用的结果, 持续的研究有利于做出较合理的解释。

     

    Abstract: Because of its high nutritive value and extensive use, potato has become a critical crop in the southern mountain areas of Ningxia, China. However, the expansion of cultivated land areas under potato has made not only crop rotation difficult, but as has also worsened the obstacles of potato continuous cropping in recent years. In order to alleviate and eventually resolve the obstacles of potato continuous cropping, rhizosphere soils were sampled under the following potato treatments after 2 years, 7 years and 11 years of continuous cropping in the southern mountain areas of Ningxia, China. Terminal restriction fragment length polymorphism (T-RFLP) was used to study the genetic diversity of soil microorganisms, to explore the dynamics of main soil microbial groups in rhizosphere soils and to find the possible reasons for the obstacles of potato continuous cropping in the region. The results showed that some specific T-RFs fragments changed or disappeared in rhizosphere soil samples under different periods of continuous cropping, though higher polymorphism of T-RFLP of bacteria and fungi in rhizosphere soils of continuously cropped potato was observed. While the Shannon-Wienen, Simpson and Sorenson indexes of bacterial dropped, those of fungus increased with increasing years of continuous cropping. Analysis of soil microorganism biota revealed that Firmicute, Bacilli and Clostridia were the highest proportion of total bacteria communities in potato rhizosphere soils. Continuous cropping significantly changed structures of soil bacteria and fungi communities. While the proportions of Bacilli and Sphingobacteria decreased or even disappeared with increasing cropping years, β-proteobacteria and Deinococci proportions increased. The proportion of Dothideomycete and Capnodiales of fungi community in rhizosphere soils dropped whereas that of Sordariomycete and Hypocreales grew. The results suggested that potato continuous cropping limited the population of beneficial microbes such as Bacillus, while boosting that of pathogenic bacteria such as Ralstonia in the rhizosphere soils. In conclusion, soil microbial diversity in rhizosphere soils under different periods of continuous cropping was obviously influenced. The fall of the diversity of bacteria community gave way to the rise of fungi community under continuous cropping, causing imbalance in microbial community and soil micro-ecological/environmental deterioration. The obstacle of continuous cropping possibly resulted from complex interaction of multiple soil factors in rhizosphere soils. There was therefore the need for continuous field research to help comprehensively determine the mechanism of continuous cropping obstacle.

     

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