Abstract: 【Objective】 As an effective way to alleviate a continuous cropping obstacle, nutrition medium cultivation has been widely used. However, cropping obstacles still happen in nutrition medium cultivation after years of cultivation. Because of insufficient study on the mechanism and repair methods, replacement of the nutrition medium is the main method to solve the problem of a continuous cropping obstacle, resulting in the wasting of resources. The objectives of this study were to analyze the soil microbial community structure and the diversity of the nutrition medium, in order to explore the mechanism of a continuous cropping obstacle and find a reasonable method of repairing a continuous cropping obstacle of nutrition medium.【Method】 An experiment of continuous cropping of cucumbers in a nutrition medium (made from straw, soil, and chicken manure) was conducted in a greenhouse in order to study the microbial community structure and diversity of the nutrition medium microenvironment. The Shannon-Wiener diversity index, the Simpson dominance index and the McIntosh index were calculated by the biology-ECO method to reveal the microbial community structure and diversity. In addition, the changes of the microbial community structure and diversity in different rotation nutrition mediums were analyzed by the principal component analysis method. 【Result】 With the increase of rotation, the average yield of cucumber reached a peak in continuous cropping stubble 5, and that in continuous cropping stubble 11 was significantly lower than in stubble 1. As for the pH value of a continuous cropping cucumber nutrition medium, it was gradually reduced with the increase of rotation, and it was significantly lower in continuous cropping stubble 13 than in stubble 1. The content of organic carbon, available nitrogen, phosphorus, and potassium of the continuous cropping cucumber nutrition medium reached the highest level at stubble 5. The available nitrogen and available potassium content in stubble 11 were significantly lower than in stubble 1, and the organic carbon and the available phosphorus content in stubble 13 was significantly lower than in stubble 1. The principal component analysis of the microbial community carbon metabolism showed that microbial carbon source utilization was significantly different after continuous cropping stubble 7. The Shannon-Wiener index, McIntosh index, and Richness index all reached peak in continuous cropping stubble 5. The Shannon-Wiener index and Richness index in continuous cropping stubble 11 began to be significantly lower than in stubble 1, The McIntosh index in stubble 13 was significantly lower than in stubble 1. Simultaneously, with the increase of rotation, the microorganism metabolic activity decreased significantly when L-Arginine, D-Galactonic acid latone, Tween 40, Tween 80, Pyruvic acid methyl ester, Methyl-D-glucoside, and N-Acetyl-D-glucosamine were used as the carbon source. On the contrary, the activity increased significantly when L-Asparagine, 2-Hydroxy benzoic acid, 4-Hydroxy benzoic acid, Putrescine, and D-Mannitol was the carbon source. 【Conclusion】 The results showed that in continuous cropping stubble 5, the average yield of cucumbers, microbial carbon metabolism, indicators of microbial diversity, and high utilization of single carbon source number were all highest. After continuous cropping stubble 11, the ability of microbial carbon metabolism declined significantly, microbial diversities were significantly reduced, microorganisms of carboxylic acid type of carbon source utilization improved significantly, so it is stated that the microbial population preferred carboxylic acid as a carbon source to get enrichment and microbial community structure appeared simplified.

Key words: cucumber, continuous cropping, nutrition medium, Biolog, microorganism, community structure, diversity