Differential morphological, physiological, and antioxidant responses of Allium cepa and Allium sativum to untreated municipal wastewater

Untreated municipal wastewater is widely used for irrigation in peri-urban agriculture where freshwater is limited, yet its effects on edible vegetable crops remain context dependent. This study evaluated the morphological, physiological, phytochemical, and antioxidant responses of Allium cepa L. and Allium sativum L. under untreated municipal wastewater irrigation compared with freshwater irrigation in a pot experiment conducted in Sialkot, Pakistan. Wastewater had higher pH, electrical conductivity, suspended solids, and organic load than control water, indicating a chemically more complex irrigation source. Relative to the control, wastewater irrigation enhanced several visible growth traits in both species. In A. cepa, plant height, stem length, leaf size, and root length increased by 2.0%, 111.8%, 95.2%, and 57.4%, respectively, whereas in A. sativum the corresponding increases were 12.9%, 9.5%, 21.1%, and 73.5%. Reproductive traits also increased, although some large proportional changes, particularly garlic flower number, should be interpreted cautiously. In contrast, wastewater irrigation reduced chlorophyll and antioxidant activity in both species. Total chlorophyll declined by 33.7% in A. cepa and 22.4% in A. sativum, while antioxidant activity decreased across leaves, roots, and stems, with the strongest reduction observed in garlic stems. Qualitative phytochemical profiles shifted between treatments, but these observations were descriptive only and were not interpreted as statistically robust treatment effects. Overall, untreated municipal wastewater promoted several external growth traits but did not improve physiological or biochemical quality-related responses. These findings indicate a mixed plant response and suggest that visible growth enhancement under wastewater irrigation should not be interpreted as evidence of improved crop quality or safety.