Manganese Toxicity Suppressing Nitrogen-Fixing Bacteria Growth and Impairing Nitrogen Uptake and Utilization in Sugarcane

Sugarcane (Saccharum spp.) is an economically vital crop used for producing sugar and bioethanol. The sugarcane grown in acidic soils of southern China suffered from severe leaf chlorosis resulting from excessive soil manganese (Mn). This study aimed to explore the effects of Mn toxicity on the physicochemical properties and microbial communities in sugarcane rhizosphere soil, as well as its impact on sugarcane growth and nitrogen uptake and utilization. The results showed that Mn toxicity significantly lowered soil pH and reshaped soil microbial communities by promoting bacterial genera such as Nocardioides and Sinomonas, which are involved in ureolysis, cellulolysis, and Mn oxidation. In addition, it inhibited genera like Nitrospirota that are associated with nitrogen fixation. This disruption hindered the conversion of soil ammonium nitrogen to nitrate nitrogen, ultimately reducing soil available nitrogen, suppressing sugarcane growth and development, and limiting nitrogen uptake. Overall, our findings highlight the importance of applying fertilizers for sugarcane cultivation in high-Mn areas.