Nutrient Removal and Oxidative Response of Barley to Eutrophic Stress

Eutrophication caused by excessive nitrogen (N) and phosphorus (P) inputs threatens aquatic ecosystems and requires sustainable solutions. Barley (<i>Hordeum vulgare</i> L.) is a fast-growing forage crop with potential for removing nutrients in eutrophic waters; however, a comprehensive understanding of its physiological responses across a wide gradient of concurrent N and P levels is still developing. To investigate this, a 7-day hydroponic experiment was conducted: six N + P enrichment levels, control (0), 70 + 7, 140 + 14, 280 + 28, 560 + 56, and 1120 + 112 mg·L^-1 of total N and P (TN:TP fixed at 10:1), were prepared in hydroponic culture and their effect on seed germination, growth, nutritional quality, photosynthetic pigments, antioxidant activity, and nutrient removal efficiency were studied. Results showed that early germination was inhibited under nutrients and enriched conditions, but this recovered by day 3. A moderate nutrient supply (NP 70 + 7) promoted seedling growth, resulting in maximum plant height, fresh weight, crude protein (6.6%), ether extract (6.1%), and chlorophyll a (10.9%) compared to the control. Root growth was best in control, while high nutrient stress (NP 1120 + 112) led to the highest mortality (23.5%). This mortality was linked to a severe suppression of the enzymatic antioxidant system (SOD, POD, and CAT), indicating a collapse of primary oxidative defense under extreme stress. Nutritional quality improved under NP 140 + 14, which yielded the lowest NDF and ADF and the highest chlorophyll b (15%) and glutathione content (14.9%). Antioxidant enzymes (SOD, POD, and CAT) were most active in the control and declined with increasing N + P levels, while glutathione peaked under NP 140 + 14. This indicates a potential shift in the plant's defense strategy, where glutathione plays a key role in mediating tolerance to moderate eutrophic stress. Nutrient removal analysis showed that N removal efficiency was highest under NP 70 + 7 (53.4%), whereas P removal decreased consistently with rising concentrations. Overall, barley grass seedlings tolerated N + P levels up to NP 280 + 28 while maintaining growth and nutrient uptake, a resilience facilitated by its dynamic antioxidant response, suggesting their potential role in phytoremediation of eutrophic waters.