Morpho-Physiological and Enzymatic Responses of Zinnia (Zinnia elegans L.) to Different Metal Hoarded Wastewaters

Wastewater, as an irrigation source, offers various advantages, significantly enhancing soil fertility, crop development, soil health, and preventing soil alkalinization. The introduction of non-conventional water resources (treated greywater, and treated wastewater) in floriculture plays a crucial role in water conservation. This study examined the impact of treated greywater (wastewater generated from domestic activities such as bathing, showering, laundry, and dishwashing) and treated wastewater (water from toilets, showers, kitchen sinks, and industrial processes) on photosynthetic characteristics, stress-related metabolites, and antioxidative enzymes in zinnia plants. A six-month pot experiment was conducted, with three water sources (canal water, treated greywater, and treated wastewater) and two zinnia varieties (Peter pan and Dreamland). During the flowering stages, when the zinnia flower petals were fully opened. Several parameters were measured, including pigments, photosynthetic attributes, total soluble protein, hydrogen peroxide and glycinebetaine. Moreover, antioxidant enzymatic activities like peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) were also investigated in zinnia plants to assess their resilience against abiotic stressors caused by high levels of heavy metals and excessive nutrients present in wastewaters. Results indicated that treated greywater (TGW) significantly improved vegetative parameters, such as plant height, leaf number, leaf area, and stem diameter. Additionally, flowering attributes, including the number and diameter of flowers, as well as fresh and dry plant biomass, increased in Peter pan variety under treated greywater irrigation. Chlorophyll and carotenoid contents were notably reduced in plants irrigated with treated greywater and treated wastewater. Photosynthetic attributes, such as stomatal conductance, transpiration rate, and photosynthetic rate, significantly improved in zinnia plants under treated greywater irrigation. Stress-related metabolites and antioxidant enzymatic activities also showed substantial enhancements under treated greywater irrigation. Principal Component Analysis (PCA) confirmed the positive effect of treated greywater on flower quality, plant biomass, and physiological processes. Utilizing treated greywater and wastewater for Zinnia cultivation is a promising approach. Ensuring the ongoing monitoring and management of harmful substances in wast