Dynamic changes in the non-structural carbohydrates of legume species in the Hulunbeier meadow steppe

Non-structural carbohydrates (NSC) play important roles in plant metabolism, regreening, and regrowth. The dynamic changes in NSC in perennial species are good indicators of grazed, mowed, and restored grassland. In this study, we examined the soluble sugar and reducing sugar contents in the shoots, stem bases, and roots of five legume species (Mellissitus ruthenica, Astragalus adsurgens, Oxytropis myriophylla, Vicia amoena, and V. sepium) in Hulunbeier meadow steppe from July 2015 to September 2016. The results showed that the soluble sugar and reducing sugar contents differed in different species and years, with the soluble sugar content in the roots of the five legume species being significantly reduced during extreme drought conditions (P < 0.05). From April through September in 2016, the maximal values of soluble sugars and reducing sugars in the shoots of V. amoena were 1.01%～7.04% and 0.54%～6.73%, respectively, whereas the contents of these sugars in the stem base were highest in V. sepium at 1.12%～10.06% and 0.52%～2.69%, respectively. Soluble sugar content in the roots of O. myriophylla and reducing sugar content in the roots of V. sepium were 1.68%～7.62% and 0.46%～2.98%, respectively, which were higher than those in the other species. Increased storage carbohydrate in plant roots can improve the resistance to grazing. Commencement and termination of livestock grazing should be late June and early September, respectively, in the Hulunbeier meadow steppe. Suitable management practices include reducing stocking rate, deferring grazing, and discontinuing grazing earlier during drought years. In addition, to promote sustainable grassland utilization, hay production should take place in the middle of August.