Elucidating the distinct interactive impact of cadmium and nickel on growth, photosynthesis, metal-homeostasis, and yield responses of mung bean (Vigna radiata L.) varieties

Contamination of soils with heavy metals (HMs) caused serious problems because plants tend to absorb HMs from the soil. In view of HM hazards to plants as well as agro-ecosystems, we executed this study to assess metal toxicity to mung bean (Vigna radiata) plants cultivated in soil with six treatment levels of cadmium (Cd) and nickel (Ni) and to find metal tolerant variety, i.e., M-93 (V₁) and M-1(V₂) with multifarious plant biochemical and physiological attributes. Increasing doses of Cd and Ni inhibited plant growth and photosynthesis and both varieties showed highly significant differences in the morpho-physiological attributes. V₂ showed sensitivity to Cd and Ni treatments alone or in combination. Tolerance indices for attributes presented a declined growth of Vigna plants under HM stress accompanied by highly significant suppression in gas exchange characteristics. Of single element applications, the adverse effects on mung bean were more pronounced in Cd treatments. V₁ showed much reduction in photosynthesis attributes except sub-stomatal CO₂ concentration in all treatments compared to V₂. The yield attributes, i.e., seed yield/plant and 100-seed weight, were progressively reduced in T₅ for both varieties. In combination, we have observed increased mobility of Cd and Ni in both varieties. The results showed that water use efficiency (WUE) generally increased in all the treatments for both varieties compared to control. V₂ exhibited less soluble sugars and free amino acids compared to V₁ in all the treatments. Similarly, we recorded an enhanced total free amino acid contents in both varieties among all the metal treatments against control plants. We conclude that combinatorial treatment proved much lethal for Vigna plants, but V₁ performed better than V₂ in counteracting the adverse effects of Cd and Ni.