Deciduous forests of the Eastern US host a variety of shrub and tree species native to Europe and Asia. Many of these invasive woody plants co-occur with native congeners in the forest understory, yet they exhibit divergent photosynthetic rates and seasonal patterns of photosynthesis. We want to understand how these differences in carbon assimilation translate to differences in carbon allocation. Higher assimilation rates in invaders, coupled with high allocation to growth constitute a resource-acquisitive strategy. We hypothesize that invaders employ this strategy in the forest understory, prioritizing new structural biomass over carbon storage pools. Thus, we expect to find lower non-structural carbohydrate (NSC) concentrations in invasive species tissues than native species. We collected stem and root tissues from three individuals each of 40 species of native and non-native woody shrubs growing in a common garden. Samples were collected following leaf abscission in the fall and leaf expansion in the spring. We then screened samples for soluble sugars and starches using high throughput near-infrared spectroscopy calibrated with colorimetry methods. Linear mixed effect models with phylogenetic correction were used to analyze the effects of plant nativity, season, carbon assimilation rate, and leaf production habit on soluble sugar and starch concentrations.
Season was a strong predictor of NSC concentration in stems and roots, with a significant reduction in storage in the spring following leaf production. Across tissue types and seasons, non-native species possessed lower soluble sugar concentrations than native species, though starch concentrations did not vary with nativity. Species with higher assimilation rates also tended to store fewer non-structural carbohydrates. Finally, species exhibiting a single leaf flush in spring tended to store more NSCs in their stems in spring and fall than species with a continuous leafing habit, but this pattern did not hold with respect to root tissues. Taken together, non-native plants exhibit different carbon storage strategies than natives, independent of assimilation rate and leaf flushing habit. Additionally, traits associated with resource conservation vary positively with storage allocation. Future research is needed to identify the costs and benefits of storage allocation strategies under varying environmental conditions. In the northeastern US, cold tolerance may be one driver of storage allocation in native woody species.