Effects of potassium application on functional diversities of microbes in rhizospheric soil of continuous cropped tobacco

This study aimed to evaluate the effects of potassium application on the functional diversity of microbial community in rhizosphere soil of continuously cropped tobacco to understand the mechanism for development of replanting disease (continuous cropping problem) in tobacco. The inhibitory effects of tobacco rhizosphere soil on lettuce and tobacco seedlings were decreased with increase in dose of potassium. BIOLOG analysis indicated that in terms of the properties using different carbon sources, the microflora was not significantly different in the rhizosphere soil of continuous cropping tobacco under different potassium doses, except for the microorganisms using phenolic acid as the carbon source. Besides the correlative analysis suggested that the autotoxic effects of tobacco in the continuous cropping system were significantly and positively correlated with the inhibitory effects of tobacco rhizosphere soil on the target plants, lettuce. Further, the inhibitory effects of tobacco rhizosphere soil on the target plants were also positively correlated to the microorganisms using the carboxylic acid, amine, and phenolic acid as carbon sources. However, the microorganisms utilizing the amine were significantly and negatively correlated with the use of carboxylic acid and phenolic acid as carbon sources. In addition, the microbe feeding on the carboxylic acid was also significantly and negatively correlated to phenolic acid. The findings suggest that it is crucial to optimize the structure of microbial community in rhizosphere soil of tobacco in the continuous cropping system by using reasonable farming practice.