Influence of nitrogen forms and mycorrhizal colonization on growth and composition of Chinese bunching onion

In recent years, interest has grown in cultivating Allium species with enhanced health benefits and/or distinct flavor. Concentrations of phytochemicals determining these desired characteristics may be influenced by nitrogen forms (ammonium or nitrate) and arbuscular mycorrhizal (AM) fungi. We examined these relations with the test plant bunching onion (Allium fistulosum L.). Three different ammonium-to-nitrate (NH4+ : NO3-) ratios were supplied in combination with or without inoculation with an AM fungus (Glomus mosseae). The plants were evaluated for dry weight, leaf number, and content of nutrients (N, NO3-, P, S), sugars (glucose, fructose, and sucrose), and organosulfur compounds (measured as pyruvic acid). The experiment was carried out under controlled conditions in a greenhouse. Plants were grown on perlite amended twice a day with nutrient solution. In nonmycorrhizal plants, the application of nutrient solution with predominant NO3- or NH4NO3 as N source supported adequate growth of Allium fistulosum while predominant NH4+ supply resulted in decreased growth and occurrence of wilting symptoms. Mycorrhizal inoculation significantly increased dry weight and leaf number of predominantly NH4+-fed or NH4NO3-fed plants. While shoot P concentration increased with higher NH4+ supply, shoot N concentration increased in predominantly NH4+-fed plants only. Nitrogen form and AM colonization had little effect on shoot S or sugar concentrations. The total content in organosulfur compounds was significantly affected by both, N form and AM colonization. The optimal growth condition for a high formation of organosulfur compounds in this experiment was a nutrient solution with predominant,NO3- supply, but when supported by AM fungi, Allium fistulosum produced similar amounts of pyruvic acid in NH4NO3-fed plants.