Effects Of Continuous Cropping Cucumber On Soil Ecosyste Properties And Cucumber Growth

As an economically important vegetable, cucumber (Cucumis sativus L.) is one of the most popular greenhouse plants. With the rapid development of horticulture in our country, the trend of a scale and specialization production in cucumber appears. Because of the restriction of plant condition and the urge of economic profits, soil sickness of cucumber is common, which severely restrichs the persistant use of horticulture and need to be solved urgently.In this paper, cucumber was continuously monocropped in pots for nine growing seasons. The growth condition of cucumber was observed. Soil phenolic compound contents, soil nutrient condition, soil bacterial, fungal and Fusarium community structures and sizes were also analyzed. Main results of this paper were as flowing:1. Cucumber of the seventh growing season showed an obvious retarded growth behavior. The leaf area, root volume and activity, and net photosynthetic rate of cucumber in the seventh growing were lower than in other growing seasons. The cucumber growth condition of the ninth growing turned better compared with the seventh growing season.2. In the continuously monocropped cucumber system, soil pH decreased from the first growing season to the seventh growing season, and increased in the ninth growing season. Soil EC increased from the first growing season to the seventh growing season, and decreased in the ninth growing season.3. The soil nutrient contents tended to increase from the first growing season to the seventh growing season. Contents of soil available nitrogen and phosphorous increase from the first growing season to the seventh growing season, and decreased in the ninth growing season. Changes of soil organic matter were not obvious in these different treatments.4. Activities of soil urease, neutral phosphatase and catalase were the lowest in the seventh growing season among these five treatments. Soil neutral phosphatase activity increased from the first growing season to the seventh growing season. Soil urease and catalase activities showed no obvious changes in the other four treatments. Soil polyphenol oxidase activity showed no obvious changes in all treatments.5. PCR-DGGE results showed that the continuous monocropping of cucumber changed soil bacterial and fungal community structures. The continuous monocropping of cucumber had stronger effects on active soil bacterial and fungal community than on total soil bacterial and fungal community, indicating that the RNA-based method was more efficient in soil community researches. The influence of the cucumber growth period on soil bacterial and fungal community structures was stronger than that of the continuous monocropping.6. Quantative PCR was used to measure the sizes of soil bacterial and fungal communities. Soil bacterial 16S rRNA gene copy numbers were significantly higher in the third growing season than that in the first growing season (p<0.05), and soil bacterial 16S rRNA gene copy numbers tended to decrease from the third growing season to the ninth growing season. Soil fungal ITS rRNA copy numbers increased with growing season from the first to the seventh growing season, and decreased in the ninth growth season.7. Continuous monocropping of cucumber changed the Fusarium community structhre. The Fusarium community size (Efla gene copy numbers) decreased in the third growing season, and increased from the third to the seventh growing season, finally decreased in the ninth growing season.8. Six kinds of phenolic compounds were detected in the soils under cucumber in the continuously monocropped system. p-coumaric acid content was the most abundant, followed by p-hydroxybenzoic acid> syringic acid> ferulic acid> vanillin> vanillic acid. The content of soil total phenolics increased with growing season from the first to the fifth growing season, and decreased in the seventh growth season, and increased in the ninth growing season.9. Amendments of phenolic compound suppressed cucumber radical elongation and seedling growth, increased soil dehydrogenase activity, microbial biomass C content, and bacterial and fungal abundances. Amendments of phenolic compound also changed soil bacterial and fungal community structures, decreased DGGE band numbers and diversity indices of the soil bacterial community structure, while increased that of the soil fungal community structure.Overall, Cucumber of the seventh growing season showed an obvious retarded growth behavior. The increase of soil EC and soil nutrient contents, decrease of soil pH, and changes of soil biological characters were closely related to the soil sickness of cucumber. Methods at the RNA level could reflect the effects of continuous monocropping of cucumber on soil microbial community composition better than at the DNA level. Phenolic compounds could directly affect the growth of cucumber, and indirectly by changing soil biological characters.