Effect of different nitrogen levels on the physiology and ecology of Paspalum wettsteinii

To understand the adaptive mechanisms of Paspalum wettsteinii in response to nitrogen and explore the level of nitrogen suitable for its growth, five nitrogen levels (1, 3, 5, 7, and 9 mmol·L^–1) were used in a pot experiment and morphological, physiological, and photosynthetic characteristics of P. wettsteinii were studied. The results showed that when P. wettsteinii was treated with 3 mmol·L^–1 of nitrogen, its growth index, biomass, and nitrogen content were higher; soluble protein (SP) content and proline (Pro) content, peroxidase, catalase, and superoxide dismutase activities were higher; chlorophyll content, net photosynthetic rate, transpiration rate, and stomatal conductance were higher; while malondialdehyde content and intercellular CO₂ concentration were lower (P < 0.05). Under nitrogen deficiency (1 mmol·L^–1) and excess nitrogen (7～9 mmol·L^–1) conditions, SP and Pro content, enzyme activities, and chlorophyll content of P. wettsteinii were reduced and plant growth was inhibited. Principal component analysis and fuzzy membership function were used to evaluate the effects of the five nitrogen levels on the performance of P. wettsteinii. The results showed that the optimum nitrogen level for the growth of P. wettsteinii is 3 mmol·L^–1.