Phenotypic plasticity of alternanthera philoxeroides in response to simulated daily warming: Introduced vs. native populations

Abstract

Aims: The evolution of increased phenotypic plasticity hypothesis predicts that populations in the introduced range of an invasive species have evolved greater plasticity than populations in the native range. Studies of this hypothesis mostly focused on the plastic evolution of invasive plants to light, water, nutrients, neighboring plants, and natural enemies. However, there are relatively few studies focusing on the evolution of plasticity in plant growth and functional traits in response to warming. The few existing studies are concentrated in temperate regions and focus on growth-related traits, but relatively little attention has been paid to tropical regions and herbivory-related traits. To address this gap, we conducted an experiment with Alternanthera philoxeroides to study whether introduced and native populations of invasive plants differ in biomass, important functional traits and herbivory resistance in response to daily warming. Specifically, we addressed the following questions: (1) How do biomass, functional traits and herbivory damage of A. philoxeroides respond to simulated daily warming? (2) Do these responses differ between introduced and native populations of A. philoxeroides? Methods: We conducted a field experiment in Zengcheng District (113.87° E, 23.33° N), Guangzhou City, Guangdong Province in which we grew eight populations of the invasive plant A. philoxeroides collected from both the introduced range (China) and the native range (Argentina) under ambient temperature and a condition of simulated daily warming of 2°C. After eight weeks of growth, we harvested all plants and measured the following variables: (1) biomass (i.e. total biomass and storage root biomass), (2) functional traits (i.e. branching intensity, specific stem length, root-to-shoot ratio and specific leaf area, and (3) herbivory damage (i.e. relative feeding area and stem-tip feeding proportion). Results: Simulated daily warming of A. philoxeroides significantly reduced total biomass (-7.8%), storage root biomass (-12.8%), branching intensity (-11.6%) and stem-tip feeding proportion (-34.4%). The reduction in total biomass caused by the daily warming was greater in the introduced than in the native populations. Simulated daily warming reduced specific stem length and stem-tip feeding proportion of the introduced populations, while the native populations showed the opposite pattern. Regardless of simulated daily warming or not, storage root biomass (+31.5%), branch strength (+38.5%), specific stem length (+30.2%), root-to-shoot ratio (+24.5%) and specific leaf area (+20.0%) of the introduced populations were higher than those of the native populations, although stem-tip feeding proportion was lower (-35.8%). Conclusion: These results indicate that simulated daily warming of 2°C in tropical regions is a stressor for the invasive plant A. philoxeroides. Biomass of the introduced populations has stronger plasticity in response to simulated daily warming of 2°C than that of the native populations. In response to simulated daily warming, plasticity of plant shape-related traits (specific stem length) and herbivory-related traits (stem-tip feeding proportion) of the introduced populations shows the opposite direction to that of the native populations. Given that the reduction in biomass reduction and increase in herbivory increase were greater in the introduced than the native populations, future temperature increases due to global climate change may not be beneficial to the abundance of invasive plant A. philoxeroides in the tropics.