喜旱莲子草对模拟全天增温的可塑性:引入地和原产地种群的比较

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

植物可以通过关键功能性状的表型可塑性来适应气候变暖背景下环境温度的增加。表型可塑性增强进化假说(evolution of increased phenotypic plasticity hypothesis)认为外来植物在引入地进化出了更强的表型可塑性。以往对该假说的验证多集中于外来植物对光照、水分、养分、邻体以及天敌等的可塑性进化,而对增温条件下植物生长和功能性状可塑性进化的研究相对较少。仅有的几项研究多集中在温带地区,且多集中于研究植物生长相关的性状,而对植物的抗性和草食作用对增温的响应的关注相对较少。本研究采用同质园实验比较了喜旱莲子草(Alternanthera philoxeroides)引入地(中国)和原产地(阿根廷)各8个种群的生物量、功能性状和草食作用在热带地区(广州市增城区)对模拟全天增温2℃的响应差异。结果表明:(1)模拟全天增温显著降低了喜旱莲子草总生物量(–7.8%)、贮藏根生物量(–12.8%)、分枝强度(–11.6%)和茎端取食率(–34.4%)。(2)模拟全天增温造成的引入地种群总生物量降低幅度大于原产地种群;模拟全天增温使引入地种群的比茎长和茎端取食率降低,而原产地种群则相反。(3)无论是否模拟全天增温,引入地种群的贮藏根生物量(+31.5%)、分枝强度(+38.5%)、比茎长(+30.2%)、根冠比(+24.5%)和比叶面积(+20.0%)均高于原产地种群,茎端取食率则低于原产地种群(–35.8%)。这些结果表明,热带地区全天增温2℃对喜旱莲子草是一种胁迫;引入地种群的生物量对模拟全天增温2℃的响应更强,而其株形相关性状(比茎长)和草食作用(茎端取食率)对模拟全天增温的可塑性方向与原产地种群相反。由于引入地种群在热带地区模拟全天增温条件下生物量的下降和草食作用的增加明显高于原产地种群,因此在未来全球气候变暖的背景下,热带地区温度升高可能不利于喜旱莲子草种群多度的增加。

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℃.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℃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℃than that of the native populations.In response to simulated daily warm ing,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.