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).