Annual soil respiration, contribution of root respiration to total soil respiration, and soil organic carbon residence time in the top 20 cm of soil.

*The estimates were derived from those of Wang et al. [54].
SR  =  annual soil respiration, HR  =  annual heterotrophic respiration, SOC  =  soil organic carbon, GR  =  grassland, SH  =  shrubland, EC  =  evergreen coniferous forest, DC  =  deciduous coniferous forest, DB  =  deciduous broadleaved forest. Different lowercase letters in mean SR and SOC indicated significant differences (P<0.05).