Zeolite application plays a significant role in mitigating the negative impacts of heavy metal stress on plants by improving soil quality and reducing the bioavailability of toxic metals such as cadmium, lead, and copper. Due to their high cation-exchange capacity and porous structure, zeolites immobilize heavy metals in the soil, thereby lowering their uptake by plant roots. This protective effect not only decreases metal-induced oxidative stress but also enhances nutrient balance, which supports overall plant growth and resilience under contaminated conditions.

In terms of physiological responses, zeolite application helps maintain chlorophyll content, which is often degraded under heavy metal stress due to oxidative damage and nutrient imbalance. By reducing metal toxicity and improving essential nutrient uptake, zeolites preserve chlorophyll synthesis, leading to improved photosynthetic efficiency. Additionally, zeolites support carbohydrate accumulation by enhancing photosynthetic activity and stabilizing metabolic processes, which are otherwise disrupted under stress conditions.

Furthermore, zeolites influence osmolyte accumulation, particularly proline, which plays a vital role in plant stress tolerance. Under heavy metal stress, plants typically accumulate proline as a defense mechanism to scavenge free radicals and maintain osmotic balance. With zeolite treatment, the level of proline accumulation may either be moderated due to reduced stress intensity or enhanced in a regulated manner to strengthen stress defense. Thus, zeolites contribute to stabilizing chlorophyll levels, promoting carbohydrate synthesis, and modulating proline accumulation, thereby improving plant tolerance to heavy metal stress.

Aqeela Saleh do you have plans to test plants with zeolites under potentially toxic metal loads, or are you interested in some other aspect of the system? My experience with zeolites (not plant growth related) is that they have contributed significant amounts of aluminium to the matrix. Obviously, depending on the quantities applied, the soil type, plant species and the specific zeolites, if applied to growing plants, excess Al may be absorbed by roots, causing an entire other suite of issues, even if the zeolite soaks up the contaminating metals you originally had.

H.A Adewuyi , do you have any references for Aqeela Saleh to back your statements with?

- How do the zeolites distinguish between potentially toxic metals and otherwise essential metals in terms of their immobilisation and reducing bioavailability in the soil?

- The abilities ascribed to chlorophyll in the plant sound too good to be real. Does the zeolite actually get in the chloroplast itself to enhance photosynthesis? What is meant by the last sentence of paragraph 2?

- Paragraph three essentially says zeolites can 1) moderate (presumably a decrease), or 2) enhance (i.e. increase) proline, which is not a useful answer unless we have the original papers to refer to.