The influence of light habitat on the physiology, biomass allocation, and fecundity of the invasive shrub Amur honeysuckle (Lonicera maackii, Caprifoliaceae)¹

Many exotic invasive plants exhibit plasticity in form and function across a range of environmental conditions, optimizing available resources in a manner that frequently outcompetes native organisms. The invasive shrub Lonicera maackii is one of the most prominent invasive plant species in the Midwestern United States. The objectives of this research were to investigate the morphological and physiological plasticity of this invasive shrub across light environments, and to study allometric parameters that will help estimate the aboveground biomass of L. maackii of all size classes. Shrubs were selected from open, forest edge, and understory habitats. Photosynthetic responses to light and leaf nitrogen content were measured throughout the growing season in 2003 and shrubs were harvested in October 2003. The maximum photosynthetic assimilation rates for open grown shrubs were more than double the values measured in the edge and understory. Maximum photosynthesis rates were strongly correlated with leaf nitrogen content, yet the photosynthetic nitrogen use efficiency was uniform across habitats. Open-grown shrubs had the highest values of total and partitioned biomass, although shrubs from all locations showed a proportional distribution to leaf, branch, trunk, and fruit. Although reproductive shrubs can produce copious amounts of fruits and seed in high light environments, fruit production still occurred in forest interior environments and is a direct source of seeds in the understory. Results suggest that because L. maackii exhibits physiological and morphological plasticity coupled with prolific fecundity (even in the understory), this species can persist in all habitats.