采集连续种植茄子4年以上的连作土壤进行室内培养，将传统的人工培养法和现代分子技术 PCR‐DGGE法相结合，旨在探明长期连作蔬菜土壤施用石灰氮和双氰胺（ dicyandiamide ，DCD）以及配施稻草后的微生物种群结构变化。结果表明：石灰氮处理能有效提高连作土壤中细菌和放线菌的数量，减少真菌的数量，提高细菌／真菌比值（B／F）和放线菌／真菌比值（ A／F），改变土壤微生物的种群结构，促使连作土壤从真菌主导型向细菌主导型转化，将失衡的微生物区系恢复到健康状态，从而起到防治土传病害的作用；双氰胺的处理效果不如石灰氮处理。 PCR‐DGGE的研究结果也表明，氰胺类肥料改变了连作土壤细菌和真菌的种群结构，产生了一些新的种属和优势种群，也对一些种群有抑制作用；氰胺类肥料均提高了土壤细菌和真菌的多样性指数和丰富度。石灰氮对连作土壤微生物种群结构的改变大于双氰胺，配施稻草明显有利于氰胺类肥料对连作土壤微生物种群结构的改善。土壤微生物区系结构的改变可能是氰胺类肥料防治土传真菌病害的主要机制之一。%With the increasing demand for vegetables , continuous vegetable cropping was more popular and common in China , which will result in seriously continuous cropping obstacle in fields . Imbalance of soil microbial community structure , decline in bio‐diversity , reduction in quantity of beneficial microorganism and accumulation of pathogenic microorganism were major factors of continuous cropping obstacles . Soil microorganism plays an important role in maintaining balance , health and high quality of soil ecosystem . Changing of microbial community structure directly influenced soil function , thereby produced negative effect on plant growth . Using artificial regulation measures such as adjusting microbial community structure and increasing bio‐diversity , was an effective method to overcome continuous cropping obstacles . Calcium cyanamide and dicyandiamide ( DCD) were cyanamide fertilizers , which had significant inhibition effect on harmful organisms , especially on pathogenic fungi in soil . However , effects of cyanamide fertilizers on microbial community structure and bio‐diversity of continuous cropping soil were unclear . n The aim of this research was to study the effects of calcium cyanamide and dicyandiamide application on microbial community structure in continuous vegetable cropping soil . Results of the study might reveal the soil micro‐ecological mechanism of calcium cyanamide and dicyandiamide to control eggplant verticillium wilt , and provide theoretical foundation and technical guidance for cyanamide fertilizers application in agricultural production . The experimental soil was silt paddy soil and was collected from farmland in Quzhou , Zhejiang Province . In the farmland , the planting years of eggplant were more than four years , and verticillium wilt of eggplant was severe and out of control in the last year . Six treatments were designed in experiments: 1) control , 2) dicyandiamide , 3) calcium cyanamide (lime nitrogen) , 4) straw , 5) dicyandiamide + straw , 6) calcium cyanamide + straw . Soils of different treatments were incubated at 25 ℃ . Through conventional artificial culture method , quantities of bacteria , fungi and actinomycetes were recorded . Community structure and bio‐diversity of bacteria and fungi were analyzed by PCR‐DGGE . n Results showed that , calcium cyanamide application effectively increased the number of bacteria , decreased the amount of fungi , improved the ratio of bacteria to fungi and actinomycetes to fungi in the continuous cropping soil . But dicyandiamide showed no distinct influence on the number of bacteria . Dicyandiamide and dicyandiamide plus rice straw application increased the ratio of bacteria to fungi with the high value of 2 .48 and 9 .96 times in the 30 days . Calcium cyanamide and calcium cyanamide plus rice straw application obviously increased the ratio of bacteria to fungi with the high value 8 .42 and 58 .39 times in the 30 days . So , application with calcium cyanamide in the continuous cropping soil could change the microbial community structure , restore the imbalance microbial community structure into a healthy status for vegetable growth by changing the dominant microbial community structure from fungi to bacteria , and then controled the soil‐borne disease in the continuous vegetables cropping soil . The results of PCR‐DGGE also indicated that , cyanamide fertilizer application altered the community structure of bacteria and fungi , induced the appearance of new species and biotic population , and inhibited some other population . In the continuous vegetables cropping soil , the diversity index and richness of bacteria were decreased with the calcium cyanamide application in the early stage ( 8 days after application) , but the bacteria community diversity and richness were increased in the later stage ( 20 days after application ) . Dicyandiamide application obviously increased the diversity index and richness of bacteria than calcium cyanamide application . The calcium cyanamide and dicyandiamide application could improve the diversity index and richness of bacteria and fungi . On the whole , the effect on microbial community structure was higher in the calcium cyanamide application treatment than in the dicyandiamide application treatment . Furthermore , cyanamide fertilizer application with rice straw addition could obviously improve the microbial community structure in continuous vegetable cropping soil . n In conclusion , calcium cyanamide , especially combined with straw application , can significantly change microbial community structure , improve imbalanced eco‐system , recover healthy ecological environment in continuous cropping soil . It might be one of the principal mechanisms for the cyanamide fertilizers showing good effects on controlling soil‐borne fungal diseases .
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