Photosynthetic energy gain and biomass energy and resource investment represent trade-offs between potential enhancements and limitations to plant productivity, respectively. We compared these characteristics in the exotic invasive Berberis thunbergii DC. with that of co-occurring natives Kalmia latifolia L. and Vaccinium corymbosum L. in a northeastern United States forest. We hypothesized that invasion by B. thunbergii could be facilitated by a lower leaf construction cost (CC) and reduced leaf nitrogen content (N) relative to photosynthetic rate (A) and maximum photosynthetic capacity (Amax), which would afford it greater energy-use efficiency (EUE) and nitrogen-use efficiency (NUE), and maximums of these variables (EUEmax and NUEmax), compared with native shrubs. Although B. thunbergii and K. latifolia exhibited similar peak-season A and Amax, EUE, EUEmax, and NUEmax were greater in B. thunbergii, which exhibited lower leaf CC and density. In contrast, EUE, EUEmax, NUE, and NUEmax did not differ between B. thunbergii and V. corymbosum given their similar A, Amax, and area-based leaf CC and leaf N. Considered with leaf phenology, our results suggest two distinct physiological mechanisms could influence B. thunbergii invasion. Specifically, deciduous B. thunbergii exhibited greater cost-effectiveness than evergreen K. latifolia, while a longer payback time for photosynthetic energy gain could offset instantaneous similarities in cost-effectiveness of earlier leafing B. thunbergii and deciduous V. corymbosum.