Coexistence of ammonium () with manganese (Mn) in acid soils may facilitate the alleviation of Mn toxicity to plants. However, the effect of on Mn toxicity and the corresponding mechanisms are unclear. In this study, the effects of and nitrate () on Mn toxicity, cell wall properties, and nitric oxide (NO) signaling in sugarcane were compared. alleviated Mn‐induced chlorosis in sugarcane seedlings and increased seedling biomass compared with . Exogenous application of decreased the root cell wall pectin content and methyl esterase (PME) activity, but increased the degree of root pectin esterification (PMD). These changes were accompanied by reductions in the Mn content in roots, leaves, root cell wall, and cell wall pectin. An analysis of adsorption kinetic revealed less Mn‐adsorption capacity in cell walls extracted from ‐fed than from ‐fed sugarcane. Mn induced NO accumulation in sugarcane roots, but ‐fed seedlings accumulated less NO. Exogenous application of the NO donor sodium nitroprusside increased the Mn content of root cell wall pectin in ‐fed sugarcane, while the NO scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxid decreased the Mn content in ‐fed sugarcane. These treatments eliminated the difference in the pectin Mn content between ‐fed and ‐fed sugarcane, as did a similar treatment with the nitrate reductase inhibitor tungstate, which decreased root cell wall pectin content and NO accumulation. These results suggest that (i) alleviates Mn toxicity in sugarcane by reducing root pectin accumulation and root cell wall PME activity, thereby increasing cell wall PMD and decreasing both the Mn‐binding capacity of cell wall and Mn accumulation, and (ii) NO mediates the accumulation of both pectin and Mn in response to different forms of nitrogen. The physiological mechanisms underlying the alleviation of ammonium on Mn phytotoxicity were clarified, which provided important implication for agricultural production and ecosystem functioning in acid soil.

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.

Background: Manganese (Mn) toxicity induces severe seedling chlorosis and growth inhibition in sugarcane cultivated on acidic soils, yet the mechanisms driving seasonal recovery and scalable mitigation strategies remain poorly defined. This study aimed to elucidate the role of iron (Fe) deposition from rainwater in natural greening and validate foliar Fe supplementation as an efficient countermeasure. Methods: We integrated field monitoring across 78 sites, phenological tracking of seasonal recovery, molecular analyses of chlorophyll biosynthesis pathways, and validation experiments (hydroponic and field trials) to investigate Fe-mediated Mn toxicity alleviation. Key metrics included leaf chlorophyll/Fe correlations, gene expression patterns, and agronomic responses to Fe treatments. Results: Field data revealed a strong positive correlation between leaf chlorophyll content and foliar Fe levels (r=0.82, p<0.01). Chlorotic seedlings achieved full visual recovery by late summer, with chlorophyll and Fe concentrations increasing 11.1- and 4.4-fold relative to spring baselines. Mechanistically, Fe reversed Mn-induced functional Fe deficiency by enhancing 5-aminolevulinic acid synthesis (2.3-fold increase) and Mg-protoporphyrin IX monomethyl ester conversion (1.8-fold increase), while downregulating FLUORESCENT expression (60% reduction) and upregulating MgPME cyclase activity (3.1-fold increase). Foliar FeSO₄ applications (0.5–1.5 g Fe L⁻¹) effectively reversed chlorosis, boosting chlorophyll content by 1.9–2.7-fold, seedling survival by 100%, and cane yield by 1.7-fold under Mn-toxic conditions, with minimal input requirements (7.5–22.5 g Fe ha⁻¹). Conclusion: Our findings demonstrate that rainwater-borne Fe is a key driver of seasonal recovery from Mn-induced chlorosis in sugarcane. Foliar Fe supplementation emerges as a cost-effective, scalable strategy for mitigating Mn toxicity, offering significant advantages over resource-intensive soil amendments for sustainable sugarcane production on acidic soils.

Manganese toxicity severely restricts the growth and yield of sugarcane in acidic soil. However, the molecular mechanism of the specific tolerance of different genotypes to manganese remains unclear. This study aims to identify and functionally characterize the ZIP manganese transporter genes in sugarcane, and to elucidate the differences in manganese regulatory mechanisms between the sensitive type GT32 (Saccharum hybrid cultivar) and the tolerant type ZZ1 (Saccharum hybrid cultivar). Through phylogenetic analysis, conserved motifs and cis-acting element analysis, as well as Ka/Ks analysis, a total of 24 ZIP genes were identified in three different sugarcane genotypes. Combined with hydroponic manganese stress treatments, quantitative reverse transcription PCR (qRT-PCR), ion concentration measurements and chlorophyll analysis, physiological and transcriptional differences between ZZ1 and GT32 were compared. Yeast complementation experiments verified the manganese transport ability of ScIRT1 and ScZIP3. Under manganese stress conditions, the results showed that the chlorophyll content of ZZ1 was 41.14% higher than that of GT32, and the manganese accumulation in roots and stems was lower. Significant differences were also observed in the transcriptional patterns of ZIP genes in roots and stems. The qRT-PCR results indicated tissue-specific differences: the transcription level of ScZIP7 in the roots of GT32 was 10 times higher, while ZZ1 maintained the high transcription level of ScZIP3 under manganese stress. The genotype-dependent expression patterns of ScIRT1, ScZIP3, ScZIP6, and ScZIP7 may contribute to the regulation of manganese uptake and intracellular distribution, thereby contributing to the enhanced manganese tolerance observed in ZZ1. These findings provide valuable insights into the molecular basis of manganese tolerance and highlight potential candidate genes for the genetic improvement in manganese-tolerant sugarcane varieties.