Responses of plant functional types to an environmental gradient on the Northeast China Transect

The hypothesis that some plant traits such as life form are robust surrogates for plant functional type (PFT) has provoked an ongoing debate. Based on a dataset from the Northeast China Transect (NECT), we attempted to test the hypothesis by comparing an objective PFT identification framework in which large datasets of plant traits were considered with two subjective PFT frameworks in which only a few plant traits were involved. Additionally, we addressed the relations between the relative abundance of PFTs and the environmental gradient represented by actual evapotranspiration (AET) along the NECT. We also discuss the changes in ecosystem functioning associated with the PFT turnover along the environmental gradient. Based on an objective PFT classification, eight PFTs were identified: deciduous trees, shrubs, perennial forbs with lower net photosynthesis, perennial forbs with higher net photosynthesis, perennial bulb-grasses, perennial tiller-grasses, annual C₄ herbs and evergreen trees. Our results indicated that some plant traits, such as life form and photosynthesis pathway, are robust surrogates for PFTs, implying that subjective approaches to PFT classification are useful. Nonetheless, caution should be used during the classification of PFTs. The framework adopted for PFT classification should depend on the specific scientific issues being dealt with. It is therefore meaningless to pursue a general framework for the identification of PFTs even within given plant communities. On the other hand, our quantitative classification of PFTs confirmed recurrent patterns with respect to PFT turnover along an environmental gradient. Furthermore, with the turnover in PFT along the NECT from the west to the east, ecosystem properties such as productivity and carbon storage are predicted to decrease, while photosynthesis is predicted to increase, suggesting that PFT turnover would inevitably lead to changes in ecosystem functioning.