Mordenite particle size and ion exchange affect photosynthetic activity and nutritional value of rocket and spinach

Mordenite is one of the most abundant natural zeolites, commonly in found volcanic rocks, and is well known for its molecular sieve properties, enabling diverse applications. In the present study, we investigated the effects of mordenite particle size and potassium ion exchange on the growth, physiological, and biochemical traits of rocket (Eruca sativa) and spinach (Spinacia oleracea). Plants were cultivated on non-modified mordenite, small (MS) and large (ML) fractions, as well as on potassium-exchanged substrates (M+ S–K and M+ L–K). Ion exchange did not affect the water-holding capacity of the small fraction but significantly reduced it in the large fraction, indicating fraction-dependent physicochemical responses to modification. The ion-exchanged large fraction promoted plant growth and improved photosynthetic performance. Furthermore, the large mordenite fraction stimulated the accumulation of polyphenols and flavonoids, and increased the antioxidant capacity of the plants, particularly under ion-exchanged conditions. These effects were more pronounced in spinach than in rocket, highlighting species-specific sensitivity to substrate properties. Overall, our findings demonstrate that the physicochemical characteristics of mordenite, including particle size and ion composition, play a key role in modulating plant physiological and biochemical responses. This study provides new insights into the application of mordenite-based substrates and highlights their potential as functional growth media for improving crop performance, nutritional quality, and resilience under controlled cultivation conditions.