Physiological responses of Scirpus validus to nitrate stress were investigated. The experiment was conducted in an artificial greenhouse over a period of 35 days. The inhibitory effects of nitrate stress on S. validus growth were greater at concentrations higher than 10 mmol·L^-1. Greater than 10 mmol·L^-1 nitrate inhibited the growth of S. validus; specifically, the fresh weight, new stem height, Δroot length, surface area, and root average diameter and volume were reduced. The level of ammonium in the plants was constant, whereas total nitrogen and nitrate nitrogen levels were reduced. Under stress, nitrate damaged the photosynthetic system and strongly reduced the net photosynthetic rate, transpiration rate, quantum yield at LCP, LSP, and P_nmax. Furthermore, nitrate increased stomatal limitation and conductance and influenced spectral parameters, e.g., reduced both PRI and SDr/SDb. The inhibitory effect of nitrate was most pronounced at 20 mmol·L^-1, primarily due to penetration and non-stomatal limitation. This study identified the physiological responses of S. validus to nitrate stress. The observed changes in physiological indices for S. validus, including photosynthetic parameters and spectral indicators, suggest that nitrate can inhibit root growth, differentiation and photosynthesis in plants, leading to an overall reduction in growth.