Effects of nitrogen form on seedling growth and its photosynthetic characteristics of forage mulberry

A hydroponic experiment was carried out to determine the effects of different proportions of nitrate and ammonium nitrogen on seedling growth and its photosynthetic characteristics of mulberry (Morus alba) variety Qinglong under the same nitrogen amount. This study indicated that the combination of nitrate and ammonium nitrogen increased the plant height, leaf number, leaf area, root length, and leaf and root biomass of mulberry seedlings when compared to application of single ammonium or nitrate nitrogen. The plant growth and biomass of mulberry seedlings were the highest when the proportions of nitrate and ammonium nitrogen were 50∶50 and 25∶75. The net photosynthetic rate (Pn), stomatal conductance (Gs) and water use efficiency (WUE) in leaves of mulberry seedlings growing in 25∶75 proportion solution of ammonium and nitrate nitrogen were higher than those of other proportion solutions. Single ammonium or nitrate nitrogen greatly improved the apparent quantum yield (AQY) and decreased the light compensation point (LCP) in leaves of mulberry seedlings. This study suggested that forage mulberry varieties Qinglong preferred to nitrate nitrogen, and the optimal proportions of nitrate and ammonium nitrogen for mulberry seedling were between 50∶50 and 25∶75.