Sugar and fructo-oligosaccharides contents in onion before snow cover and after snow melting

Growth and accumulation of sugars and fructo-oligosaccharides was investigated in fall-planted onions in the snowfall zone under different cultivation conditions: before snow cover and after snow melt. Growth of onions before snow cover was compared with that after the snow melted. Sugars and fructo-oligosaccharides accumulated in the onion leaf blades and leaf sheaths both before snow cover and after snow melt. Before snow cover, seedling time and planting time were found to affect sugar and fructo-oligosaccharides content in onion leaf blades and leaf sheaths. After snow melt, seedling time and planting time had no effect on sugar and fructo-oligosaccharide contents in onion leaf blades and leaf sheaths. The contents of sugars and fructo-oligosaccharides were lower in plants after snow melt compared with those before snow cover. The degree of polymerization of fructo-oligosaccharides in plants before snow cover was 11, whereas that in plants after snow melt was only 5. Therefore, sugars and fructo-oligosaccharides are consumed in metabolic activities and growth when plants are overwintering, and fructo-oligosaccharides with a higher degree of polymerization would be used earlier. Total sugar contents, including fructo-oligosaccharides, in plants before snow cover were positively correlated with dry matter content and negatively correlated with nitrogen content.