Effects of Potassium Application on Root Rhizosphere Microbial Community Changes and Growth of Sugarcane

This study aimed to explore the characteristics of changes in the bacterial and fungal communities and functions in the rhizosphere soil and their influences on sugarcane growth during the tillering stage under different potassium application levels, so as to provide a theoretical basis and production guidance for potassium application during the tillering stage of sugarcane.

Using the new variety YZ1696 as the experimental material, a three-year continuous field trial was conducted during the sugarcane tillering stage, applying five different potassium fertilizer levels (0, 75, 150, 225, and 300 kg·hm^-2) to investigate the effects on the growth rate of sugarcane, the structure and function of the rhizosphere soil bacterial and fungal community, and the sucrose yield of sugarcane.

(1) Within two months after potassium application during the tillering stage, the absolute growth rate of sugarcane initially increased and then decreased as the potassium application level increased. After three consecutive years of targeted application of different potassium fertilizer treatments, the growth performance of new plantings, one-year-old ratoons, and two-year-old ratoons was consistent, showing that both the sugarcane yield and sucrose content first increased and then decreased with increasing potassium fertilization gradient, and the growth rate, yield, and sucrose content of sugarcane were the optimal under a potassium application of 150 kg·hm^-2. (2) Different potassium application treatments had significantly influenced the abundance of bacteria and fungi in the rhizosphere soil and the composition of the microbial community and diversity. The differences in bacterial abundance mainly concentrated in Proteobacteria, Acidobacteriota, Actinobacteriota, Nitrospirota, and Firmicutes, while the differences in fungal abundance mainly concentrated in Basidiomycota, Ascomycota, and Chytridiomycota. The structure and diversity of the rhizosphere bacterial and fungal communities exhibited a trend of decreasing first and then increasing with the increase in potassium application level, and a fertilization inflection point was at a potassium application of 150 kg·hm^-2. (3) Correlation analysis between the abundance of the main microbial communities and the sucrose yield of sugarcane under different potassium application treatments indicated that the abundances of bacterial Actinobacteriota and fungal Proteobacteria, Basidiomycota, Ascomycota, and Chytridiomycota were significantly correlated with the sucrose yield of sugarcane. These microorganisms played positive roles in nitrogen fixation, organic matter decomposition, nutrient cycling, and inhibition of pathogenic bacteria in the soil.

Appropriate potassium application during the tillering stage could improve the structure and function of the rhizosphere soil microbial community, thereby promoting sugarcane growth. However, different potassium application levels had varying effects on sugarcane yield, sucrose content, the functional microbial communities of bacteria and fungi, among which the potassium application level of 150 kg·hm^-2 had the most significant effect on optimizing the structure of the soil microbial community and enhancing the sucrose yield of sugarcane.