Figure 2 Partial correlations between topsoil Δ14C and four environmental factors in alpine grasslands based the available datasets provided by Chen et al.(2021). The partial correlation between Δ14C and each environmental factor is calculated by using the other three factors as the control variables. The partial correlation is also performed in alpine steppe and alpine meadow separately. Similar to Chen et al. (2021), precipitation is the first principal component (PC1) of mean annual precipitation (MAP), precipitation of the wettest month (PWM), and precipitation of the wettest quarter (PWQ); temperature is the PC1 of mean annual temperature (MAT), minimum temperature of the coldest month (MTCM) and mean temperature of the coldest quarter (TCQ); Plant C input is the PC1 of plant carbon input in topsoil, normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and leaf area index (LAI); mineral protection is the PC1 of molar ratios of dithionite- and oxalate-extractable Fe/Al oxides to SOC (Fed + Ald and Feo + Alo), and the molar ratios of exchangeable Ca2+ (Caexe) and Mg2+ (Mgexe) to SOC. Logarithm transformation is performed for the four variables of mineral protection before principal component analysis (PCA).