Effects of tobacco-stalk biochar returning on soil nutrients，the structure and functioning of bacterial communities in tobacco-planting yellow-brown fields

【Objective】 In order to explore the effects of tobacco-stalk biochar（BC）on soil nutrients the structure and functioning of bacterial communities in tobacco-planting yellow-brown fields， and provide theoretical basis for the utilization of tobacco stalk.【Method】 A field experiment with different biochar dosages（0， 5， 15， 20， 40 t/ha）was set up to compare the changes of soil nutrient indexes and bacterial abundance of tobacco field after four years’application. The 16S rDNA high-throughput sequencing and PICRUSt gene prediction analysis were used to decipher soil community composition，diversity and metabolic function.【Result】The results showed that soil pH， organic matter， total nitrogen， available phosphorus， available potassium and the abundance of soil bacteria significantly increased with the dosage of biochar application. The results of principal coordinate analysis（PCoA）and cluster analysis show that soil bacterial community composition was significantly altered by the biochar application. When the amount of tobacco-stalk biochar was 15 t/ha， bacteria OTU richness and Alpha diversity indexes were higher than other treatments. At the phylum level， the relative abundance of Proteobacteria and Actinobacteria was lower under 15 t/ha than other treatments， but those of Gemmatimonadetes， Chloroflexi， Planctomycetes and Nitrospirae were high. At the genus level， the relative abundance of Gemmatimonas， Flavisolibacter，Roseiflexus was higher under 15 t / ha than other treatments. Redundancy analysis（RDA） analysis showed that biochar application dosage was significantly positively correlated with the relative abundance of Bacteroidetes （P<0.05，the same below）， while negatively correlated with Acidobacteria. PICRUSt functional prediction analysis suggested that biochar application increased the functional gene abundance related to soil carbon metabolism in bacterial community.【Conclusion】 After applying tobacco-stalk biochar to the yellow-brown tobacco-planting soil in Guizhou，soil nu-trients，agronomic and economic indicators of flue-cured tobacco are improved，and the richness and diversity of soil bacterial communities are significantly increased. The carbon metabolism ability of soil bacteria is enhanced，which has a positive effect on improving the soil microecology of tobacco fields. In sum，the effect of using 15 t/ha tobacco-stalk biochar isrelatively better and can be popularized in tobacco production.