| Cucumber(Cucumis sativus L.), a crop of very important facility vegetable cultivation of crops, high yield and economic importance, loved by the people in many countries, is vulnerable to soil sickness. In this regard, many researchers have carried out a series of studies, such as selected anti-cropping varieties, applied organic fertilizer and biocontrol, grafting culvation, soil sterilization. Although these methods have achieved some success, these problems have yet to be addressed. Soil microbial diversity can be changed by diversification managements and influence neighboring crops or next-season crops. Some research indicated that cover crop of wheat can significantly alleviate the phenomenon of continuous cropping obstacle, but the mechanism is unclear. The former researched respectively the mechanism of different cover crop alleviate continuous cropping obstacles from the point of allelopathy and soil nutrient resources utilization. But in the soil conditions, whether the role of allelopathy and soil nutrient resources utilization of wheat played a role or not in soil conditions. If two effects are present, who played a bigger role, these problems are still not clear.We studied the allelopathic effect of wheat influence on cucumber growth, on nutrient resource utilization of cucumber by adding activated carbon, washed and burned whear, soil sterilization, adding nutrient treatment. The effect of wheat on soil microbial community abundance, composition and structure were studied and researched changes in soil microbial community caused by soil amended with wheat can exert feedback on cucumber growth. The above experiments cleared that the wheat of allelopathic effect and nutrient resource utilization to alleviate the cucumber continuous cropping obstacle, deepen the understanding of the mechanism of soil amended with wheat alleaviating cucumber continuous cropping obstacles and provide cultivation mode of wheat and a theoretical basis and technical support of related research. The main results were as follows:(1) Nutrient results showed: cucumber seedling soil available nutrients content and trace nutrients content were reduced, and soil water soluble phenol and complex phenol content were also decreased after planting wheat, but the soil organic matter and total phenolic content were increased. Cover crop of wheat treatment increased plant N, P, K content and decreased plants Mn, B, Ca, Mo, Si content of cucumber seedlings, but improved plant uptake Mn, B, Ca, Mo, Si content. These indicated that soil amended with wheat changed soil available nutrient content and promoted cucumber growth and nutrient absorption.(2) After overcoming soil nutrient difference between amended and unamended with wheat, there was no effect on cucumber soil EC value and p H in different periods. The shoot and root fresh and dry weight were reduced when soil amended with wheat and adding nutrient at 20 d. These showed that the differences of soil nutrient content caused by soil amended with wheat were not main reason in promotion of cucumber growth.(3) Soil amended with wheat promoted cucumber growth. But cucumber seedling growth was inhibited when soil adding activated carbon, removed plant and adding activated carbon, washed and burned wheat treatment. These indicated that soil amended with wheat has not only allelopathic effect but other effect on cucumber growth.(4) We studied soil first plant wheat and sterilized, then soil amended and unamended with wheat. The difference of two treatment was not significant at 10 d.These indicated that root exudates and/or plant secondary metabolites of wheat does not work in the absence of soil microorganisms(directly but not indirectly).(5) Miseq sequencing results showed that soil amended with wheat influence soil bacterial and fungal community structure. The W treatment increased the abundance of Acidimicrobiia, Alphaproteobacteria, Acidobacteria, Betaproteobacteria, Gemmatimonadetes, Deltaproteobacteria, Sphingobacteriia, Thermoleophilia, Dothideomycetes, Eurotiomycetes, Pezizomycetes, Sordariomycetes, but decreased the abundance of Actinobacteria, Anaerolineae, Clostridia, Gammaproteobacteria, Flavobacteria.(6) The q PCR results showed that soil amended with wheat changed the number of Pseudomonas and Bacillus. The number of soil Pseudomonas and Bacillus W treatment was significantly lower than that of treatment UW. DGGE and clone library results showed that soil amended with wheat changed soil Pseudomonas community structure and composition. The Pseudomonas species of soil amended with wheat was increasing with the growth of cucumber seedlings. The diversity of soil Pseudomonas was highest at 20 d.(7) The experiment of soil sterilization results showed that if(W- UW)% >(W-A-UW-A)%(fresh and dry weight), the difference of cucumber seedlings growth caused by soil amended and unamended with wheat was due to different soil microorganisms. Plant-soil feedback results showed that soil amended with wheat changed the soil microbial community structure and produced positive feedback effects on cucumber growth.Overall, soil amended with wheat promote cucumber growth. The reason was not the difference of soil nutrients caused by soil amended and unamended with wheat, but may be root exudates and/or plant secondary metabolites during wheat growth process and wheat straw decaying process changed soil microbial community structure and composition. Changes in soil microbial community can have positive feedback on cucumber growth... |
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