Effects of dominant plant species change on soil multifunctionality in alpine meadows of the three-river source region

Alpine meadows are an important ecosystem in the Three-River Source Region of the Qinghai-Tibet Plateau. The dominant plant species in alpine meadows undergo changes during degradation that may directly or indirectly influence soil functionality. In this study, the effects of variations in the dominant plant species on soil physi-cochemical properties and multifunctionality were analyzed. Quadrats with different dominant plant species were classified as CY (for Cyperaceae), CGF (for Cyperaceae-Gramineae-Forbs), and FB (for Forbs). The results showed that, for all cases, there were significant correlations among TN (Total Nitrogen), SOC (Soil Organic Carbon), TP (Total Phosphorus), soil water, and bulk density, whereas TK (Total Kalium) showed no clear correlations with other properties. The most significant correlation between plant community characteristics and soil physicochemical properties was found in CGF because of the higher biodiversity and intensity of intermediate competition. Species with absolute dominance had stable positive or negative effects on soil multi-functionality at almost all thresholds. The effects of Cyperaceae decreasing and Forbs increasing on soil multifunctionality were nonlinear. Turning points of important values of Cyperaceae (-0.38 and 0.66) and Forbs (-0.34 and 0.69) were observed in dominant species changes. The different effects of Cyperaceae and Forbs on soil multifunctionality before and after the turning point indicate that the effect of plant communities on soil multifunctionality depends more on the interactions between species that remain rather than those that depart. The results of this study can guide efforts to maximize both plant communities and soil multifunctionality for the protection and restoration of alpine meadows.