Introduction: Sugarcane (Saccharum spp.) is a crucial crop for sugar and bioethanol production. However, sugarcane grown in the acidic soils of southern China often suffers from severe leaf chlorosis due to excessive soil manganese (Mn). This study investigates 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.Methods: Soil samples were collected from sugarcane fields with varying levels of Mn toxicity. Physicochemical properties of the rhizosphere soil were analyzed, including soil pH, available nitrogen, and microbial community composition. The impact of Mn toxicity on sugarcane growth was assessed through measurements of plant biomass, leaf chlorosis, and nitrogen uptake efficiency.Results: Mn toxicity significantly lowered soil pH and altered the soil microbial community structure. Bacterial genera such as Nocardioides and Sinomonas, which are involved in ureolysis, cellulolysis, and Mn oxidation, were promoted. In contrast, genera like Nitrospirota, associated with nitrogen fixation, were inhibited. This disruption hindered the conversion of soil ammonium nitrogen to nitrate nitrogen, reducing soil available nitrogen. Consequently, sugarcane growth and development were suppressed, and nitrogen uptake was limited.Discussion: The findings highlight the detrimental effects of Mn toxicity on sugarcane cultivation in high-Mn areas. The altered microbial community composition and reduced soil nitrogen availability directly impact sugarcane growth. These results underscore the importance of applying appropriate fertilizers to mitigate Mn toxicity and improve soil fertility in such regions. Future research should focus on developing strategies to enhance soil nitrogen cycling and promote beneficial microbial communities to support sustainable sugarcane production.

Manganese toxicity has limited sugarcane (Saccharum spp. hybrid.) growth and production in acidic soils in south China. The rhizosphere plays an irreplaceable role in plant adaptation to soil abiotic stress, but the responses of the sugarcane rhizosphere to manganese toxicity are still unknown. We designed pot experiments in Mn-rich acidic soil, collected the sugarcane rhizosphere and bulk soil samples, and then investigated the changes in Mn-related soil parameters and microbiome. The results indicated that the water-soluble and exchangeable manganese concentrations in the sugarcane rhizosphere were significantly lower than that in the bulk soil, which was not associated with soil pH changes. In contrast, the number of bacteria and the activity of peroxidase, sucrase, urease, and laccase in the rhizosphere were significantly higher. The 16S rDNA sequencing results showed that the bacterial diversity and quantity along with the abundance of Proteobacteria in the rhizosphere were significantly higher than in the bulk soil, while the abundance of Acidobacteria was lower than in the bulk soil. The soil laccase activity and the number of bacteria decreased significantly with the increase in the manganese toxicity stress. Finally, the relative abundance of proteins associated with manganese transportation and oxidation was significantly higher in the rhizosphere soil. In summary, the Mn-induced response of the rhizosphere is an important mechanism in sugarcane adaptation to manganese toxicity in acidic soil.

We had previously reported that manganese (Mn)-induced chlorosis is a serious problem in ratoon sugarcane seedlings grown in acidic soils. To further monitor the progression of chlorosis and elucidate the corresponding mechanism, both plant growth and nutrient status of sugarcane plants and soils were investigated in the growth seasons of ratoon cane seedlings in 2016 and 2018. The impacts of rainfall and ammonium on chlorosis were also investigated hydroponically. The results showed that the chlorotic seedlings could green in mid-summer; Mn content in the first expanded leaf decreased significantly, whereas iron (Fe) content increased significantly during the progression of greening. The leaf Mn content in the greened seedlings decreased by up to 78.1% when compared with that in the initial chlorotic seedlings. The seedlings also showed a significant increase in seedling height and weight of the expanded leaves, accompanied by a decrease in plant Mn content during the progression of greening. Moreover, young seedlings with less Mn content showed earlier greening than older seedlings with more Mn content. The exchangeable ammonium content in the soils increased significantly during the progression of greening, and the addition of 1 mM ammonium to the chlorotic seedlings resulted in a decrease in leaf Mn content by up to 80%. Furthermore, leaf SPAD value and Fe content increased by 2.0-fold and 1.4-fold, respectively, after rainwater was applied to the chlorotic seedling. These results indicate Mn-induced chlorotic seedlings can turn naturally green, and downregulation of plant Mn content, rainfall in summer, and soil ammonium contribute to the greening of chlorotic seedlings.

Introduction: Sugarcane ( Saccharum spp .) is an economically important crop cultivated primarily for sugar and bioethanol production. In southern China, sugarcane grown in acidic soils often exhibits severe leaf chlorosis owing to excessive soil manganese (Mn) levels. However, the mechanisms by which Mn toxicity disrupts soil nitrogen (N) cycling, particularly the roles of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in regulating nitrification and N availability in sugarcane, remain unexplored. Methods: To address this gap, we conducted laboratory soil incubation experiments and greenhouse pot trials using four treatments consisting of combinations of two N levels (N1:0.14 g·kg ^-1 ; N2:0.28 g·kg ^-1 ) and two Mn levels (−Mn: 0 mg·kg ^-1 ; +Mn: 328 mg·kg ^-1 , simulated using anhydrous Mn sulfate), along with a blank control (CK). Key measurements included rhizosphere soil physicochemical properties, AOB/AOA community structure, nitrification potential, and sugarcane N uptake efficiency. Results: Results showed that Mn toxicity significantly reduced soil pH and nitrification potential by 75.9–78.0% compared to non-Mn treatments, and AOB amoA gene abundance by 44.9–46.5%, while altering AOB/AOA community composition. Redundancy analysis (RDA) identified soil organic carbon, total nitrogen, and ammonium nitrogen as the primary drivers of AOB community shifts, whereas exchangeable Mn, ammonium nitrogen, and pH dominated AOA community changes. Correlation analysis confirmed that nitrification potential and AOB amoA abundance were strongly positively linked to sugarcane N accumulation and uptake efficiency, which decreased by 47.3–53.4% under Mn toxicity due to reduced nitrate availability. Discussion: These findings indicate that Mn toxicity impairs sugarcane N utilization by disrupting ammonia-oxidizing microbial communities and suppressing nitrification, thereby providing insights for optimizing N management strategies in Mn-contaminated acidic soils.