气候变暖背景下植物可通过关键性状的表型可塑性来适应环境温度的增加。表型可塑性增强进化假说预测定植到新环境中的入侵植物种群具有演化出更强表型可塑性的潜力。此前对可塑性进化的研究涵盖了外来植物性状对水分条件、光照变化、土壤养分、邻体根系以及天敌防御等的响应, 而较少有研究关注增温条件下植物重要性状的可塑性进化。已有的部分研究多集中在温带和热带地区, 而较少关注入侵植物在高寒地区对增温的响应; 且研究多集中在植物生长相关性状, 较少关注功能性状和防御性状。本研究采用同质园实验比较了喜旱莲子草6个引入地(中国)种群和6个原产地(阿根廷)种群, 在西藏拉萨模拟全天增温2℃处理下的适合度性状、功能性状和防御性状的响应差异。结果表明: (1)高寒地区模拟全天增温显著提高了喜旱莲子草总生物量(+36.4%)、地上生物量(+34.5%)、贮藏根生物量(+51.4%)和毛根生物量(+33.6%), 降低了分枝强度(-19.8%)和比茎长(-30.2%); (2)模拟全天增温使引入地种群的比叶面积和黄酮含量增加, 而原产地种群则相反。这些结果表明高寒地区全天增温2℃对喜旱莲子草可能是一种有利条件。引入地种群的适合度性状对模拟全天增温2℃的响应比原产地种群更强, 而其光能利用相关性状和防御性状的响应可能提升了其在高寒地区的适合度。因此, 在未来全球气候变暖的背景下, 高寒地区温度升高可能更有利于喜旱莲子草引入地种群的定植和扩散。

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.