Effect of corn-stalk biochar on soil microbial functional diversity and bacterial community in cinnamon soils

Biochar application was considered as an effective way of carbon sequestration of soil. It has been known to improve both soil water and nutrient holding capacity. As a key indicator of soil fertility, microorganism plays an important role in soil ecosystem. It was necessary to understand the influence of biochar application on microbial community and functional diversity in calcareous cinnamon soils for rational utilization of biochar in cinnamon soils. A pot experiment with five biochar application levels 0 g.kg^-1 (as control), 5 g.kg^-1, 10 g.kg^-1, 30 g.kg^-1 and 60 g.kg^-1 was conducted to investigate the response of soil microbial activity and diversity, using Biolog analysis and high-throughput sequestration (HiSeq). The results showed that the average rate of color change (AWCD) decreased with increasing biochar application level, and the AWCD values were in the order of 5 g.kg^-1 control > 10 g.kg^-1 > 30 g.kg^-1 > 60 g.kg^-1 treatments. There was no significant difference between control and 5 g.kg^-1 treatments in terms of AWCD. The soil microbial community diversity index (H′) and richness index (S) also decreased, but evenness index (E) increased with increasing biochar application level. Compared with the control, biochar application rates at 5 g.kg^-1, 10 g.kg^-1, 30 g.kg^-1 and 60 g.kg^-1 increased H′ by 0.16%, 0.88%, 3.14% and 11.09%; increased S by 2.82%, 11.27%, 18.31% and 47.89%; and increased E by 1.14%, 3.00%, 3.73% and 13.76%; respectively. Principal component analysis showed that carbon substrate utilization of soil microbial community was significantly affected by 10 g.kg^-1, 30 g.kg^-1 and 60 g.kg^-1 biochar application. HiSeq analysis showed that soil bacterial OTU enhanced significantly by 1.09%, 5.26% and 24.42%, respectively, in 10 g.kg^-1, 30 g.kg^-1 and 60 g.kg^-1 biochar treatments, meanwhile, the richness index (Chao1) was increased by 5.73%, 10.21% and 37.68%, respectively, compared with that of control. Biochar enhanced the abundance of bacteria and decreased the evenness of soil bacterial distribution. Proteobacteria abundance was significantly increased by 32.3%, 21.1% and 16.7%, respectively, under 10 g.kg^-1, 30g.kg^-1, 60 g.kg^-1 biochar treatment, while Bacteroidetes abundance decreased obviously by 22.1%, 55.3%, 66.8% and 50.5%, respectively, compared with those of control. The results indicated that the rational dosage of biochar application was not more than 5g.kg^-1 (soil dry) in calcareous cinnamon soil to maintain the microbial community structure and activity.