Abstract:

Aims: Phenotypic plasticity for key traits in plants can adapt in response increasing temperatures seen through climate change. Under the evolution of increased phenotypic plasticity hypothesis, populations of invasive species have greater phenotypic plasticity than native populations. Studies of this hypothesis have mostly focused on the plasticity of invasive plants to light, water, nutrients, neighbors, and natural enemies. Studies focusing on these key plant traits under warming conditions are mostly concentrated in temperate and tropic regions, while alpine regions are overlooked. Additionally, these studies mostly focus on plant growth-related traits, while relatively little attention has been paid to plant resistance and the secondary metabolites of defense traits in response to warming, especially in alpine region. Here, test for differences in plant fitness traits, important functional traits, and defense traits in response to daily warming between introduced and native populations of invasive plants. Specifically, we explore the following questions: (1) Will the phenotypic plasticity of fitness traits, functional traits and defense traits of the invasive plant Alternanthera philoxeroides respond to daily air warming? (2) If so, does this response differ between introduced and native populations? (3) Does this response differ between alpine regions and tropic regions?
Methods: Using 6 populations of the invasive plant A. philoxeroides from the introduced region in China and 6 populations from their native region in Argentina, we conducted a field experiment to simulate a daily warming of 2℃ in Lhasa City, Tibet Autonomous Region (Alpine region: 91.04° E, 29.64° N) from August to October 2020. We placed plants from each of the 12 populations into the control plots and the warming plots, and each treatment had three replicates. There were a total of 72 experimental units in the experiment (2 origins × 6 populations × 2 temperature treatments × 3 replicates). After 8 weeks of growth, we harvested all plants and measured the several variables. The fitness traits we measured included total biomass, ground biomass, storage root biomass and hair root biomass. The functional traits we measured included branching intensity, specific stem length, root-to-shoot ratio, and specific leaf area. The defense traits we measured included triterpenoid saponins and flavonoids.
Results: Simulated daily warming of 2℃ significantly increased the total biomass of A. philoxeroides (+36.4%), the ground biomass (+34.5%), the storage root biomass (+51.4%), the hair root biomass (+33.6%), and reduced the specific stem length (-30.2%) and branching intensity (-19.8%). Simulated daily warming of 2℃ increased the specific leaf area (+15.1%) and flavonoids (+8.9%) of the introduced populations, while the native populations showed the opposite effect (-22.9%, -30.0%).
Conclusions: These results indicate that simulated daily warming of 2℃ in alpine regions is a positive condition for the invasive plant A. philoxeroides. The fitness traits of the introduced populations have greater plasticity to simulated daily warming, and the plasticity of some plant functional traits and defense traits of the introduced populations may have greater fitness in alpine regions. As a consequence, we conclude that increasing temperatures due to global climate change may be beneficial to colonization and spread of introduced populations of A. philoxeroides in the alpine region.

Key words: warming, phenotypic plasticity, plant invasion, evolution