<p>This study investigated whether leaf leachates of <i>Aizoon canariense</i> disrupt nutrient acquisition, photosynthesis, and cellular redox homeostasis in four economically important crops: wheat (<i>Triticum aestivum</i>), barley (<i>Hordeum vulgare</i>), rapeseed (<i>Brassica napus</i>), and mung bean (<i>Vigna radiata</i>).&#xa0;Seedlings were grown under greenhouse conditions and treated with 10% and 15% aqueous leaf leachates. Growth, nutrient uptake, photosynthetic characteristics, oxidative stress indicators, osmoprotectants, non-enzymatic antioxidants, and antioxidant enzymes were evaluated. The chemical composition of the leaf leachates was determined using gas chromatography–mass spectrometry (GC–MS).&#xa0;Leaf leachates significantly and dose-dependently reduced macro- and micronutrient uptake, chlorophyll content, net photosynthesis, stomatal conductance, PSII efficiency, water-use efficiency, and relative water content, with mung bean showing the greatest sensitivity. These physiological impairments were accompanied by increased hydrogen peroxide, malondialdehyde, and electrolyte leakage, indicating severe oxidative damage. Although treated plants accumulated osmoprotectants and antioxidant metabolites, these responses were insufficient to restore cellular redox balance. GC–MS identified 37 secondary metabolites, indicating a chemically complex allelopathic mixture.&#xa0;The findings support the hypothesis that <i>A. canariense</i> leaf leachates impair crop performance through coordinated disruption of nutrient uptake, photosynthetic function, and redox homeostasis. This study provides new physiological evidence of the multifaceted mechanisms underlying the allelopathic activity of <i>A. canariense</i>. Further research under field-relevant exposure conditions and with purified bioactive compounds is needed to determine the ecological significance and potential agricultural applications of these findings.</p>