Sustainable Mitigation of Tungsten Nanoparticle Contamination via Chitosan‐Driven Regulation of Photosynthesis and Lignin Metabolism in Chickpea

Tungsten nanoparticles (WNPs) impose severe phytotoxicity, highlighting the need for sustainable mitigation strategies. Here, we investigated the physiological and metabolic mechanisms by which chitosan nanoparticles (CSNPs) alleviate WNP stress in chickpea. Seeds were primed with 20 μg mL −1 CSNPs and grown in soil contaminated with 500 mg kg −1 WNPs. WNP exposure markedly suppressed growth and triggered oxidative stress, whereas CSNP application restored biomass accumulation, increasing shoot and root dry weight in response to CSNPs (by 76%–129%) and CSNPs + WNPs (by 99%–109%). CSNPs improved photosynthetic performance, as reflected by an increase in net photosynthetic rate, partially compensating for the high reduction induced by WNPs, and thereby enhanced carbon assimilation. Consequently, soluble sugars and starch accumulated in shoots and roots by 39%–70% under combined CSNP and WNP treatment. Increased carbon availability promoted amino acid biosynthesis, including glutamine, glutamate, proline, and phenylalanine, which function in osmotic adjustment and antioxidant defense, and activated the phenylpropanoid pathway via enhanced phenylalanine ammonia‐lyase activity, thereby contributing to the mitigation of nanoparticle‐induced stress. The enhanced phenylalanine pool was preferentially channeled into lignin biosynthesis via upregulation of COMT and CAD, resulting in a 130%–161% increase in lignin content. Collectively, these findings demonstrate that CSNPs mitigate WNP toxicity by restoring photosynthetic carbon flux and reallocating assimilates toward stress‐responsive metabolites and lignin‐based structural defense.