3.3 Ecosystem stocks of SOC, TN, and affecting factors
SOC stocks at 0–10 cm were significantly higher than those at 10–40 cm soil depth (P <0.05, Fig. 2a). GE significantly increased SOC stock at 0–40 cm soil depth compared to that observed after implementing the grazing methods, with the maximum increase at 0–10 cm soil depth (P<0.05, Fig. 2a, c, and Fig. 3a). GE decreased the contribution of topsoil (0–10 cm) SOC stock to the total stock compared to that obtained using grazing methods, with contributions of 30.64% (GE), 43.95% (CG), 34.32% (MG), and 41.55% (RG) (Fig. 3a). GE significantly reduced soil N stocks from 20 to 40 cm, with the maximum decrease being observed at 10–20 cm (P <0.05, Fig. 2b, d, and Fig. 3b). GE increased the contribution of topsoil (0–10 cm) TN stock to the total stock with contributions of 47.89% (GE), 37.81% (CG), 34.61% (MG), and 31.11% (RG) (Fig. 3b). Both SOC and TN stocks did not significantly change among grazing methods; however, SOC stocks in RG and MG increased by 20.93% and 27.27%, respectively, and TN stocks in RG increased by 9.06% compared to those observed with CG (Fig. 2c, d).
GE significantly increased the ecosystem organic carbon stocks (EOCs) and decreased ecosystem total nitrogen stocks (ETNs) (P <0.05) (Table 2). There were no significant changes among the results of different grazing methods (P >0.05); however, the EOCs increased by 22.29% (MG) and 16.31% (RG), while ETNs increased by 7.76% (RG) compared to those observed with CG (Table 2). MG and RG significantly increased the contribution of SOC and decreased the contribution of plant carbon to EOCs compared with GE and CG (P <0.05). Implementation of grazing methods significantly increased the contribution of soil N stock and decreased the contribution of plant N stock to ETNs when compared to the contributions associated with GE, and there were significant differences between MG, RG, and CG (P <0.05, Table 2).