Adequate characterization of soi
l organic carbon (SOC) fractions is essentia
l to e
lucidate carbon dynamics in permafrost-affected ecosystems. SOC and its fractions were investigated across a
lpine ecosystems, inc
luding a
lpine swamp meadows (ASM), a
lpine meadows (AM) and a
lpine steppes (AS), in permafrost regions on the Qinghai–Tibet P
lateau (QTP), southwest China. The density separation method was used to separate the SOC into
light- and heavy-fraction organic carbon (LFOC and HFOC, respective
ly). Permafrost soi
ls in the ASM had higher SOC, LFOC, and HFOC contents than in the AM. LFOC and HFOC contents were significant
ly corre
lated, but both were more c
lose
ly re
lated to SOC than to each other. On the eco
logica
l gradient from ASM to AS, the thickness of surficia
l organic horizons decreased whi
le the thickness of minera
l materia
ls increased. SOC in the organic horizon and permafrost had high minera
lization probabi
lity. At soi
l depths of 0–200 cm in ASM, AM, and AS, the SOC stocks were 123, 71, and 25 kg m−2 ; LFOC stocks were 70, 49, and 12 kg m−2 ; and HFOC stocks were 58, 37, and 15 kg m−2 , respective
ly. These resu
lts show that SOC fractions vary with vegetation type and active
layer thickness, thus making SOC sensitive to
changes in environmenta
l conditions. Therefore, the decomposition of SOC in permafrost-affected soi
ls of the QTP cou
ld be acce
lerated over a
degrading permafrost and under a warming climate.