Abstract: Soil P availability is a key factor restricting ecosystem function of alpine grasslands. However, the effects of grazing regimes and intensities on the soil P transformation remain unclear. We conducted a grazing experiment in an alpine grassland on the Qinghai-Tibet Plateau, with no grazing as the control, and two grazing regimes: continuous grazing and rotational grazing, each with three intensity levels: light, moderate and heavy. We investigated the responses of soil P fractions under different grazing patterns. The Tiessen-Moir sequential extraction method was used to analyze rhizosphere soil P fractions, including labile P [Resin-P, sodium bicarbonate Pi/Po (NaHCO₃-Pi/Po)], moderately labile P [sodium hydroxide Pi/Po (NaOH-Pi/Po)], and stable P [dilute hydrochloric acid Pi (D.HCl-Pi), concentrated hydrochloric acid Pi/Po (C.HCl-Pi/Po), and Residual-P]. The results showed that grazing regime, intensity, and their interaction had no significant effect on components of labile P and moderately labile P. However, NaOH-Po content in the light continuous grazing, light rotational grazing, and heavy rotational grazing treatments was 154.3% to 161.1% higher than that in the control, indicating that rotational grazing and light continuous grazing were conducive to increasing the moderately labile Po pool. Under continuous grazing, the mean C.HCl-Pi content was significantly lower by 23.9% compared to the control. Furthermore, grazing regime significantly affected soil carbon-to-nitrogen ratio, with continuous grazing showing a significant increase of 21.0% compared to rotational grazing. Total C and total N contents were highest under heavy continuous grazing, increasing significantly by 6.5% and 26.6%, respectively, compared to the control. Correlation analysis confirmed that soil total C was significantly positively correlated with NaHCO₃-Pi and C.HCl-Po, while total C and organic C were significantly negatively correlated with Resin-P. Soil C/P was significantly negatively correlated with NaOH-Po and Residual-P, reflecting complex C-P coupling effect. In summary, rotational grazing and light continuous grazing were more advantageous in maintaining soil P availability. We recommended that rotational grazing be prioritized in the alpine grasslands of the Qinghai-Tibet Plateau, thereby achieving long-term balance in soil P supply.

Key words: alpine grassland, grazing, P fraction, Tiessen-Moir sequential extraction method