Variations in foliar stable carbon isotopes among functional groups and along environmental gradients in China - a meta-analysis.

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.