Variations in foliar stable carbon isotope signatures (δ(13)C) of different plant functional groups (PFGs) and their relationships with environmental factors in China were investigated in this meta-analysis. There were some significant, but small differences in δ(13)C among PFGs categorised by life form (<1‰). Trees (-26.78‰) and shrubs (-26.89‰) had similar mean δ(13)C that were significantly higher than those of herbs (-27.49‰). Evergreen shrubs (-25.82‰) had significantly higher mean δ(13)C than deciduous shrubs (-26.92‰). Perennial herbs (-26.83‰) had significantly higher mean δ(13) C than annual herbs (-27.10‰). Grasses (-26.46‰) had significantly higher mean δ(13)C than forbs (-26.96‰). For pooled data, δ(13)C was significantly and negatively correlated with mean annual precipitation (MAP) and mean annual temperature (MAT), while it was significantly and positively correlated with latitude and altitude. There was a threshold value of MAP along the gradients, and δ(13)C did not change significantly with higher rainfall. The δ(13) C of PFGs changed with altitude, suggesting that increases in δ(13)C with altitude cannot be generalised. Differences in δ(13)C between PFGs were generally much <1‰ and therefore insignificant. In contrast, MAP and MAT had relatively large effects on δ(13) C (more than 4‰ between extremes). The δ(13)C of some PFGs responded to environmental gradients in the same manner, while their 'rates' of change were significantly different in some cases. This information could help predict potential changes in the distribution of PFGs in response to future climate change.

ABSTRACT. This paper examines the carbon isotopes ( 13 C, 14 C) of soil organic carbon (SOC) and soil CO 2 from an evergreen broadleaf forest in southern China during the rainy season. The distribution of SOC  13 C, and SOC content with depth, exhibits a regular decomposition of SOC compartments with different turnover rates. Labile carbon is the main component in the topsoil (0-12 cm) and has a turnover rate between 0.1 and 0.01 yr 1 . In the middle section (12-35 cm), SOC was mainly comprised of mediate carbon with turnover rates ranging between 0.01 and 0.025. Below 35 cm depth (underlayer section), the SOC turnover rate is slower than 0.001 yr 1 , indicating that passive carbon is the main component of SOC in this section. The total production of humus-derived CO 2 is 123.84 g C m 2 yr 1 , from which 88% originated in the topsoil. The middle and underlayer sections contribute only 10% and 2% to the total humus-derived CO 2 production, respectively. Soil CO 2  13 C varies from 24.7‰ to 24.0‰, showing a slight isotopic depth gradient. Similar to soil CO 2  13 C,  14 C values, which range from 100.0‰ to 107.2‰, are obviously higher than that of atmospheric CO 2 (60-70‰) and SOC in the middle and underlayer section, suggesting that soil CO 2 in the profile most likely originates mainly from SOC decomposition in the topsoil. A model of soil CO 2  14 C indicates that the humus-derived CO 2 from the topsoil contributes about 65-78% to soil CO 2 in each soil gas sampling layer. In addition, the humus-derived CO 2 contributes ~81% on average to total soil CO 2 in the profile, in good agreement with the field observation. The distribution and origin of soil 14 CO 2 imply that soil CO 2 will be an important source of atmospheric 14 CO 2 well into the future.