Effects of potassium fertilizer on rhizosphere microbial diversity and community assembly in sugarcane.

The abundant and rare populations of microorganisms in the ecosystem play a crucial role in preventing pathogen transmission, regulating nutrient cycling, facilitating pollutant degradation. However, less attention has pain on the agroecosystems. We conducted a field experiment to evaluate the effects of different potassium application rates (0, 75, 150, 225, 300 kg·hm^-2) on the microbial diversity, the driving factors and the microbial community assembly process of the sugarcane rhizosphere through the high-throughput sequencing and ecological mode-ling techniques. The results showed that the potassium application exerted a significant effect on soil nutrient content and soil enzyme activities, which were highest at the application rate of 300 and 225 kg·hm^-2, respectively. The abundant populations mainly concentrated in a few dominant species. Potassium application significantly affected species composition and community structures of the rhizosphere microorganisms. Under potassium application, soil urease, soil organic matter, and catalase were the key limiting factors, which could affect community structures of the abundant and rare microbial populations. The effects of potassium application on the rhizosphere bacterial community were greater than those on the fungal community, and the effects on the abundant microbial community was greater than that on the rare one. Community assembly of bacteria and fungi were predominantly driven by determini-stic processes in the sugarcane rhizosphere, with the heterogeneity selection dominating in bacteria and the homogeneity selection dominating in fungi. The deterministic processes played a key role in the abundant and rare communities assembly. In conclusion, our results demonstrated that potassium application significantly affected soil nutrients and enzyme activities. The potassium application could enhance the diversity of abundant and rare populations of bacteria and fungi and regulate soil microbial community assembly in the rhizosphere.