Plant functional traits of a shrub invader relative to sympatric native shrubs

Woody expansion has been documented for years in many different systems, often the result of anthropogenic changes to the environment. Causes and consequences of woody expansion have been well documented, but comparatively few studies have focused on functional traits that mechanistically allow for dramatic expansion in range. Our objectives were to investigate functional traits and plant resource strategies that contribute to rapid expansion of an invasive, nitrogen-fixing shrub, Elaeagnus umbellata Thunb. (Elaeagnaceae) compared with two sympatric native shrubs, Clethra alnifolia L. (Clethraceae) and Vaccinium corymbosum L. (Ericaceae). We quantified morphological, physiological and biochemical functional traits linked explicitly to three main resources that directly influence plant growth: light, water and nutrients. We attribute high photosynthetic efficiency found in E. umbellata to traits associated with light capture and use (e.g., specific leaf area, pigment concentrations, leaf display). Compared to coexisting species, leaf-level water demand was supported through high hydraulic capacity, yet E. umbellata also maintained high water use efficiency evident in delta C-13 values. Fixed nitrogen allowed for higher foliar %N observed in E. umbellata. This supports both high rates of electron transport and hydraulic capacity as seen in the relationships between foliar %N and electron transport rate (ETR) and percent loss of conductivity (PLCmidday). Overall, functional traits of E. umbellata allowed for high resource acquisition that when combined contribute to success in a wide variety of habitats. Conversely, native sympatric shrubs exhibited functional traits representative of slower-growing species (e.g., lower light capture, water use and nutrient acquisition). Our results support the hypothesis that traits associated with photosynthesis, water use efficiency, specific leaf area and leaf N are under selective pressure and highlight the importance of relationships among photosynthetic efficiency, hydraulic capacity and leaf N content that allow for the success of an expanding woody species.