Unraveling the impacts of nano-scale carbon exposure on nitrogen metabolism during early seedling establishment in Zea mays L. roots

Elucidating the relationship between extraneous nano-scale carbon properties and the metabolomic response of early Zea mays L. seedling establishment roots is crucial to reveal nano-carbon regulation and nutrient transport mechanisms.

Herein, humic acid and graphite nanoplatelets represented typical organic and inorganic morphologies of nano-scale carbon. We used equimolar exogenous carbon inputs (0.4, 2, 4 mol C kg⁻¹) to investigate the regulation of nitrogen metabolism using LC-MS, phenotype and physiology of root, nitrogen metabolism-related enzyme activities and endogenous hormones.

Our findings demonstrate that humic acid and graphite nanoplatelets promote root thickening and branching. The most prominent effects on root vitality, injury intensity, and total active absorption area were observed with 2 mol C kg⁻¹ graphite nanoplatelets and 4 mol C kg⁻¹ humic acid. The trend of nitrogen metabolism activity remained consistent, involving the assimilation of NR and NiR and the primary synergistic regulation of GO and GOGAT. Notably, 2 mol C kg⁻¹ graphite nanoplatelets induced the dynamic and selective up-regulation of pyruvic acid and down-regulation of tyramine and methyl phosphate, resulting in changes in energy metabolism and a small subset of amino acid metabolism. 4 mol C kg⁻¹ humic acid resulted in the down-regulation of the organic acids (L-asparagine, pyruvic acid, L-aspartic acid, L-glutamine, and fumaric acid), which are involved in nitrogen metabolism-related processes.

Overall, these findings highlight additional graphite nanoplatelets regulated nitrogen assimilation and protein synthesis pathways to improve nitrogen availability. Nano-carbon demonstrated the potential to reprogram agricultural traits.