Carbon Dots With Concurrently Tunable Photoluminescence and Nanozyme Activity for Agricultural Stress Resistance: A Carbonization Degree‐Mediated Strategy

Carbon dots (CDs) are emerging in agricultural nanotechnology owing to their tunable photoluminescence, biocompatibility, and nanozyme activity. Herein, we used an acid‐regulated strategy to synthesize CDs with gradient carbonization degrees, systematically elucidating their structure–performance relationships. At the nanoscale, the progressive carbonization not only induced an emission mode transition from dual to single emission (fluorescence shifting from red molecular to blue carbonized domains with a continuous spectral blue shift), but also concurrently enhanced the material's superoxide dismutase‐like activity. Structural characterization and theoretical calculations revealed that progressive carbonization generates sp 2 ‐conjugated domains, where edge‐site carbonyl (C═O) groups serve as catalytic sites for SOD‐like activity. At the organismal level, simulated salt‐stress experiments showed that highly carbonized CDs most effectively alleviated oxidative damage and promoted the growth of maize, rice, and soybean seedlings. At the field level, field trials coupled with high‐throughput phenotyping confirmed that CDs significantly enhanced crop stress resistance under saline‐alkali conditions, increasing maize yield by 144% ( n = 30, 3 biological replicates). This work establishes a structure‐activity framework wherein the carbonization degree synergistically modulates optical and enzymatic functionalities, using a representative precursor system (Pyronin B) as a proof‐of‐concept. While the general applicability of this strategy to other CDs‐based systems warrants further investigation, the present study provides a theoretical basis for the rational design of carbon‐based nanozymes and offers practical strategies for crop yield enhancement in saline‐alkali agroecosystems.