Endpoint‐specific dose‐response of nitrogen‐doped carbon quantum dots in tomato seed germination and root elongation revealed by fluorescence imaging

BACKGROUND It is important to understand how nano‐enabled materials influence plants in order to interpret concentration‐dependent responses and assess agricultural potential. This study evaluated nitrogen‐doped carbon quantum dots (N‐CQDs) in two independent tomato ( Solanum lycopersicum L.) assays involving seed germination and seedling root exposure. RESULTS The synthesized N‐CQDs were approximately 3 nm in diameter, water‐dispersible, and photoluminescent. Tomato seeds and 3‐week‐old seedlings were exposed to 0–400 mg L −1 N‐CQDs by seed soaking and root immersion for 48 h, respectively. Germination showed a peaked response, increasing from 56.67% in the control to 82.50% at 50 mg L −1 , followed by weaker stimulation at higher concentrations. In the seedling assay, plant height and fresh weight increased significantly at all tested concentrations, with no decline up to 400 mg L −1 . A constrained Hill1 model provided a descriptive fit to the mean relative growth index trajectory ( R 2 = 0.9994) and yielded an estimated half‐maximal effective concentration (EC 50 ) of 67.91 mg L −1 , indicating an apparent tendency toward stabilization at higher concentrations. Whole‐plant fluorescence imaging revealed concentration‐associated signals that were more evident in visible root and basal‐stem regions immediately after treatment and gradually decreased over 25 days. These signals were interpreted as treatment‐associated optical dynamics rather than direct evidence of nanoparticle uptake, translocation, or accumulation. CONCLUSION Tomato responses to N‐CQDs differed between the two assays, showing that concentration–response patterns depended on exposure and growth context. The findings provide a quantitative basis for further evaluation of N‐CQDs in plants, although denser concentration gradients, direct exposure quantification, physiological measurements, and longer term safety assessments remain necessary.