Nitrogen addition alters aboveground C:N:P stoichiometry of plants but not for belowground in an Inner Mongolia grassland

Nitrogen (N) deposition exhibits significant impacts on ecosystem functions and processes. Previous studies have indicated that N addition has an impact on the stoichiometry of plant leaf C:N:P ratios. However, few studies have focused on effects of N addition on belowground systems. This study aims to examine the impact of seven years of N addition on aboveground and belowground C:N:P stoichiometry at plant community level in a temperate grassland located in Inner Mongolia. A 7-year field N addition experiment was conducted, which included six treatments: Cont: control; N1: 0.4 mol·m-2 N; N2: 0.8 mol·m-2 N; N3: 1.6 mol·m-2 N; N4: 2.8 mol·m-2 N; N5: 4 mol·m-2 N with six replicates. Aboveground and belowground plant biomass and C:N:P stoichiometry were measured and analyzed. Our results showed that N addition resulted in a reduction of aboveground C concentration, but an increase in aboveground N and P concentrations, with a decrease in C:N and C:P ratios and an increase in N:P ratio. Furthermore, the aboveground C, N, and P pools all exhibited an increase as a result of N addition. However, N addition did not have any significant effect on belowground C, N, P concentrations, ratios, pools, or stoichiometric characteristics in the soil layers of 0-10 cm, 10-30 cm, 30-50 cm and 50-100 cm. These results suggest that increasing levels of N deposition significantly alter the aboveground C:N:P stoichiometry at the plant community level, which may affect functions and processes in the grassland ecosystem, but have little effect on belowground C:N:P stoichiometry.