How far can it go? Tolerance of seeds and seedlings of an invasive tree to water deficit and high temperatures

Abstract

The ability of non-native plant species to tolerate water scarcity and high temperatures, especially during the early stages of development, may influence their invasive potential. Ligustrum lucidum is a tree native to warm temperate areas of Asia. To understand the potential expansion of this non-native invasive species into more arid regions, we conducted an experiment in incubation chambers to evaluate seed germination under different water potentials and the response of its seedlings under different water availability and temperature scenarios. Seeds were collected from central Argentina and placed to germinate under four different water potentials (-0.2; -0.4; -0.7 and -1.2 MPa) created with polyethylene glycol 6000. Additionally, L. lucidum seedlings were subjected to contrasting levels of water availability combined with different periods of exposure to high temperatures. Germination measurements (germination percentage, velocity, and synchronicity) decreased at lower water potentials. No germination occurred at -0.7 and -1.2 MPa. The seedlings showed a slight increase in mortality and a significant reduction in most of the growth variables under low water availability, while exposure to high temperatures had significant effects only on chlorophyll estimate. The germination response of L. lucidum to water deficits could pose a significant constraint on its establishment in arid ecosystems. Nonetheless, this constraint may be alleviated by the species´ prolific propagule production, coupled with asynchronous seed germination, which may help it exploit more humid micro-sites or sporadic water events. Furthermore, the drought tolerance of its seedlings strongly warns against the use of this species as an ornamental plant in arid environments.