Performance, plasticity, and acclimation of the nonindigenous shrub Lonicera maackii (Caprifoliaceae) in contrasting light environments

Abstract

Growth and photosynthetic capability of the eastern Asiatic shrub Lonicera maackii (Rupr.) Herder were measured in shadehouses and in artificial canopy gaps. In shadehouses providing 5, 25, and 100% of full sun, total dry mass, and leaf area of seedlings increased with light availability; specific leaf area and leaf area ratio decreased with light availability. When small suppressed shrubs were transplanted from a forest site to the shadehouse environments, rapid (13 day) acclimation in existing leaves initially produced the highest mean photosynthetic rate (8.12 μmol∙m−2∙s−1) and the highest mean relative stem growth at 25% light. However, maximum mean photosynthetic rate (10.36 μmol∙m−2∙s−1), higher mean stomatal density, and increased mean leaf thickness were measured only in new leaves formed in 100% light. This plastic response was associated with higher relative stem growth later in the experiment. Naturally established seedlings in both artificial canopy gaps and sites with intact canopies had low and negative relative stem growth, presumably as a result of light limitation. The results support the observation that L. maackii is a shade intolerant species that performs best in forests where large disturbances or edge effects create enhanced light availability. Key words: acclimation, forest edge, invasive species, Lonicera maackii, plasticity, shade tolerance.