Exploring grazing intensity effects: nitrogen uptake in grassland species and soil carbon allocation

Background and aims: Grazing drives carbon (C) and nitrogen (N) dynamics of grasslands through livestock trampling, defoliation, and excretion. Still, the responses of N uptake by plant species and simultaneous C allocation into the soil to grazing intensity remain unclear. Methods : In-situ  15NH4+ / 15NO3− and 13C-CO2 labeling experiment was conducted in Inner Mongolia grasslands under 5 years of grazing with no, light (4 sheep 1.33 ha−1) and heavy (12 sheep 1.33 ha−1) intensity to reveal the contribution of plant-derived C into the soil and the fate of N on day one and three after 13C-labeling. Experiment had a completely randomized design (n = 3), and every plot included Leymus chinensis, Carex korshinskyi, Cleistogenes squarrosa, and Stipa grandis. Results: Grazing increased plants’ total N uptake compared to control (no grazing); higher NO3− uptake was found compared to NH4+ (aboveground: 0.40–20.78 vs. 0.32–6.58 µg N m−2; belowground: 0.04–9.92 vs. 0.01–0.49 µg N m−2), irrespective of grazing intensity. C. korshinskyi showed the highest N uptake (3–21 µg N m−2) under the three grazing intensities. 13C-CO2 assimilation was the lowest under heavy grazing (aboveground: 1.06–10.67 mg C m−2; belowground: 0.25–1.53 mg C m−2) regardless of plant species. 13C-CO2 assimilation by L. chinensis and C. squarrosa decreased 3–5 times with grazing intensity. Grazing increased 13C-SOC irrespective to soil depth compared to no grazing. Conclusions: Grazing patterns affected the plants’ total assimilation C capacity and N uptake and the response varies among plant species, as well as the allocation of plant-C transfer into the soil. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.