Comparison of leaf functional trait plasticity between exotic and native Ligustrum species in Japan.
Preventing invasion and expansion of exotic species into urban forests is an important current issue. In Japan, Ligustrum lucidum Ait., an invasive tree, has escaped into urban forests, and could compete with Ligustrum japonicum Thunb., a congenetic native species. Here, we measured intra- and inter-individual variation(plasticity) of leaf functional traits of the two species to compare their acclimation and adaptation potentials to variable light environments. We found no difference between species in intra-individual plasticity of leaf functional traits (leaf mass per area, chl and N contents per leaf area, and maximum photosynthetic rate). For many traits, inter-individual plasticity was greater for L. lucidum. This difference was due to the low plasticity of L. japonicum trees artificially planted in high-light conditions because, for example, the plasticity of photosynthetic rate of L. japonicum in its native light range was similar to that of L. lucidum. Our study suggested that the high photosynthetic capacity of L. lucidum resulting in fast growth in high-light environments such as the forest edge, may contribute to its invasiveness. In addition, L. lucidum exhibits high acclimation potential of leaf functional traits across a wide range of light environments, which could contribute to its invasion and expansion not only at the forest edge, but also the forest interior, where it could potentially compete with L. japonicum.