Responses of Non-structural Carbohydrates and C:N:P Stoichiometry of Bothriochloa ischaemum to Nitrogen Addition on the Loess Plateau, China

Bothriochloa ischaemum: (L.) Keng is an excellent native pasture and forage species on the Loess Plateau, China, which is low in soil nitrogen. Little is known about the effects of N addition on biomass, concentrations of non-structural carbohydrates (NSCs), and the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of B. ischaemum in this area. We examined these responses in both plant tissues and soil to N additions of 0 (N0), 2.5 (N1), 5.0 (N2), and 10.0 (N3) g N m(-2) year(-1). Biomass was maximal with N additions between 2.5 and 5.0 g N m(-2) year(-1). The increase in biomass was more rapid above- than belowground. N addition had no significant effect on the C:N:P ratios in the plant tissues, except for the aboveground biomass N:P ratio which increased significantly. The response to N addition of aboveground biomass and the N:P ratio suggests that N is not likely the limiting nutrient for the growth of B. ischaemum when biomass N:P ratios are between 25.5 and 27.1. In contrast to the plant tissues, the soil C:N and C:P ratios, but not the N:P ratio, decreased significantly with increasing N addition, indicating that N addition may help improve soil quality in this area. Both above- and belowground NSC concentrations varied significantly with N addition, with maxima of 102.4 g kg(-1) in N1 and 49.6 g kg(-1) in N2. The application of N could be a management option for improving ecosystem biomass production and NSC concentrations in the grasses on the Loess Plateau.