Morphological plasticity: A comparative study of leaf traits between exotic honeysuckle (Lonicera japonica) and its native congener (Lonicera sempervirens)

Background/Question/Methods

Biological invasion, one of the major processes of global change is continuously rising in its intensity in the biota. With an estimated 137 billion dollar annual deficit in the U.S. alone, there is an urgent need to understand the mechanisms of invasion. How can invasive species be so detrimental? What types of biophysical traits can enable species to function this way? In this study, we attempted to answer these questions by comparing the leaf traits of exotic invasive (Lonicera japonica) and native (Lonicera sempervirens) honeysuckle species using multivariate analysis of variance (MANOVA) method. By examining and comparing multiple traits including leaf biomass, specific leaf area, leaf thickness, stomatal length and density, main leaf vascular bundle size, proportion of photosynthetic tissues, and leaf nitrogen and carbon contents on mass basis of both species, we were able to test the hypothesis that the invasive honeysuckle outperforms its native congener owing to its possession of suites of advantageous biophysical traits associated with its leaves.

Results/Conclusions

Our results indicate that significant differences exist in leaf traits, which are directly related to plant photosynthetic capacity or carbon gain, between the two species. Specifically, higher carbon gain (both in biomass and carbon content), larger proportion of photosynthetic tissues, thicker leaves, larger stomatal size, higher stomatal density, and larger leaf vascular tissues were associated with the exotic species. Larger leaf area and higher nitrogen content on mass basis were found in the native species. Our results reveal that the leaves of the invasive honeysuckle are morphologically optimized for a higher CO₂ gas exchange and faster carbon gain. Furthermore, the lower nitrogen content found in the invasive honeysuckle leaves characterizes the invader with a relatively high nitrogen use efficiency, which enhances its growth potential. We conclude that combination of advantageous leaf traits enable the exotic honeysuckle to be more plastic and successful compared to its native congener in the invaded ecosystems.