Effects of high levels of nitrogen and phosphorus on perennial ryegrass (Lolium perenne L.) and its potential in bioremediation of highly eutrophic water

The conservation and management of rain and water in a city environment are a crucial aspect of sustainability. Sponge cities are a solution for the remediation of excessive water consumption, high pollution, and rainstorm waterlogging in urban areas. Perennial ryegrass (Lolium perenne L.) is a common species and promising bioremediation plant for the construction of sponge cities. It could be useful to purify high nitrogen and phosphorus content in wastewater runoff, but its response to high total nitrogen (TN) and total phosphorus (TP) levels has not been studied. The present study aimed to evaluate the effects of high TN + TP level on seed germination, plant growth, antioxidant response, and assimilation rate of N and P in perennial ryegrass. Compared with the control, treatments with 20 mg/L N + 4 mg/L P (20N4P) significantly decreased germination potential at day 3, but the germination rate at day 10 was similar between all treatments and the control, suggesting that a high TN + TP concentration might delay germination, but not prevent it. Treatment with 20N4P also induced significant withering and decreased shoot length, root length, and dry shoot weight of ryegrass seedlings, compared with the control. Treatments with 80N16P significantly decreased levels of chlorophyll a (Chl-a) and chlorophyll b (Chl-b), demonstrating inhibition of photosynthesis. Compared with the control, treatment with 40N8P increased the carotenoid (Car), malondialdehyde (MDA), and glutathione (GSH) content, which might alleviate oxidative stress induced by high TN + TP concentration. Moreover, high levels of TN + TP (160N32P and 320N64P) significantly reduced the removal capacity of N and P by plants. Overall, the present results provide a theoretical foundation for the development of ryegrass for bioremediation of wastewater during construction of sponge cities.