Effects of Nitrogen on Ramie (Boehmeria nivea) Hybrid and Its Parents Grown under Field Conditions

Excessive nitrogen supply has resulted in environmentally negative impacts. In order to select and develop N-effcient ramie cultivars in increased N application environments, the morphological, physiological and biochemical responses of a ramie hybridization line (Chuanzhu 11) and its conventional parents (C9451 and R79-20) to N fertilizer were investigated under rain-fed conditions during three consecutive growing seasons. Two contrasting nitrogen levels (low nitrogen, LN- 20kg ha-2; high nitrogen, HN- 120kg ha-2) were used. Results indicated that high N substantially promoted the growth of ramie plants and led to remarkable increase in fiber yield in all cultivars during the three growing seasons. Such increase was also recorded in net photosynthesis, transpiration rate and stomatal conductance, as well as chlorophylls and carotenoids. However, high N supply caused no alteration or increase in intercellular CO2 (Ci) and Ci/ Ca (ambient CO2) ratio, depending on species. Moreover, high N application significantly improved soluble protein and proline content while it reduced malondialdehyde content. The activities of superoxide dismutase and catalase also elevated, whereas peroxidase activity decreased by high N application in all cultivars. Furthermore, hybrid cultivar Chuanzhu 11 exhibited better performance as compared to its parents C9451 and H7920 due to improved growth, fiber yield, leaf gas exchange traits and enzymatic and non-enzymatic antioxidant systems under high N supply conditions. In conclusion, ramie hybrid cultivar Chuanzhu 11 was more efficient to absorb and utilize high levels of N. This meets the need for uptake and utilization of high concentration of N in increased N fertilizer environments.