Carbohydrate reserves in the rhizome of Leymus chinensis in response to nitrogen additions

The results showed that the stored carbohydrates of the L. chinensis rhizome consisted of fructan, mannitol, sucrose, fructose, and glucose. Fructan, which contributed 60% of total non-structural carbohydrates (TNC), was the predominant stored carbohydrate followed by mannitol, which contributed 20% of TNC. Both fructose and glucose were less than 15% of TNC and sucrose was only 6% of TNC. Hence, sucrose, a main component of stored carbohydrates in other grasses, was only a minor component of L. chinensis. Nitrogen rates significantly influenced the contents of fructan, mannitol and total carbohydrates, but had little effects on glucose, fructose and sucrose content in the L. chinensis rhizome. The total carbohydrate, fructan and mannitol concentrations increased in the rhizome with increasing N application rates from 0 to 17.5 g N·m~(-2), but carbohydrate reserves were reduced at application rates of 28 g N·m~(-2). The timing of N application also significantly influenced the contents of carbohydrate reserves; L. chinensis stored more carbohydrates in the rhizome when N was applied in July than that in April. In conclusion, fructan and mannitol are important stored carbohydrates in the rhizome of L. chinensis. Both N application rates and timing of application significantly affect the levels of carbohydrate reserves, especially fructan and mannitol in the L. chinensis rhizome.