Long-term excessive application of K2SO4 fertilizer alters bacterial community and functional pathway of tobacco-planting soil

To improve tobacco leaf quality, excessive K2SO4 fertilizers were applied to soils in major tobacco-planting areas in China. However, the effects of K2SO4 application on soil microbial community and functions are still unclear. An eight-year field experiment with three kinds of K2SO4 amounts (low amount, K2O 82.57 kg hm-2, LK; moderate amount, K2O 165.07 kg hm-2, MK; high amount, K2O 247.58 kg hm-2, HK) was established to assess the effects of K2SO4 application on the chemical and bacterial characteristics of tobacco-planting soil using 16S rRNA gene and metagenomic sequencing approaches. Results showed that HK led to lower pH and higher nitrogen (N), potassium (K), sulfur(S) and organic matter contents of the soil than LK. The bacterial community composition of HK was significantly different from those of MK and LK, while these of MK and LK were similar. Compared to LK, HK increased the relative abundance of predicted copiotrophic groups (e.g. Burkholderiaceae, Rhodospirillaceae families and Ellin6067 genus) and potentially beneficial bacteria (e.g. Gemmatimonadetes phylum and Bacillus genus) associated with pathogens and heavy metal resistance, N fixation, dissolution of phosphorus and K. While some oligotrophic taxa (e.g. Acidobacteria phylum) related to carbon, N metabolism exhibited adverse responses to HK. Metagenomic analysis suggested that the improvement of pathways related to carbohydrate metabolism and genetic information processing by HK might be the self-protection mechanism of microorganisms against environmental stress. Besides, the redundancy analysis and variation partitioning analysis showed that soil pH, available K and S were the primary soil factors in shifting the bacterial community and KEGG pathways. This study provides a clear understanding of the responses of soil microbial communities and potential functions to excessive application of K2SO4 in tobacco-planting soil.