Net primary productivity (NPP) is a fundamental ecosystem measurement of how much carbon (C) is allocated to growth in a given ecosystem and is a key parameter in vegetation and climate models. Improving estimates of NPP at ecosystem and global scales is critical to understanding and predicting future C stocks, especially in light of the pressing need to predict atmospheric carbon dioxide concentrations. However, it is logistically unrealistic to directly measure the total growth of vegetative biomass over large spatial and temporal scales. One approach to predict NPP is to apply continuous plant functional traits that are related to differences in NPP. Despite a strong theoretical framework, few empirical data exist to quantitatively link plant traits to NPP directly. Here, we assessed the ability and relative strength of 14 traits to predict NPP (total oven-dried biomass in g day-1) in 30 herbaceous Asclepiasspecies grown under common garden.
We identified four plant strategies defined primarily by gas exchange, leaf nitrogen and biomass allocation among leaves, stems and roots. Although some traits generally predicted NPP across all species (e.g., leaf area, plant height), most trait-NPP relationships were context dependent based on differences among plant strategies. Our results suggest that some commonly used traits have limited general predictive ability in part because similar NPP can be achieved via alternative plant strategies based on leaf-level and whole-plant tradeoffs.