大空间尺度上天敌逃逸对互花米草入侵成功影响的异质性及其遗传分化和表型可塑性驱动机制

Biotic interactions hypothesis predicts that the strength of plant-herbivore interactions will increase with decreasing latitude. However, exotic plant may exhibit dissimilar latitudinal variation in the strength of their interaction with native herbivores, because of the absence of coevolutionary history. This may generate the heterogeneity in the strength of enemy release on invasion success of exotic plants at large spatial scale. This is an area that still remains to be explored. Taking an important exotic invasive species Spartina alterniflora and a native species Phragmites australis in the coastal areas of our country as a study system, this project aims to explore differences between these two plant species in latitudinal variation of insect herbivory, and to assess effects of insect herbivory on the growth performance and competition relationship of S. alterniflora and P. australis in different latitudinal regions by using herbivore exclusion experiments in field. Results of these studies will reveal the spatial heterogeneity in effects of enemy release on the invasion success of S. alterniflora and its ecological consequences. In addition, through the impact analysis of plant trait clines and changes in community composition of insect herbivores in field, and the common garden experiment, this project also aims to reveal the different roles of the genetic differentiation and phenotypic plasticity of plants in driving the latitudinal variation of herbivory in S. alterniflora and P. australis. Project results will improve our understanding of the mechanism of success invasion of exotic plant at biogeographical scales, and will be important for the improvement and development of the relate theories of biological invasion. This project also will provide a guide and reference to the control and management of S. alterniflora.

生物互作假说认为“植物-天敌”互作强度会随纬度的降低而增加。然而，由于缺乏共同进化史，外来植物与土著天敌互作的强度可能具有不同的纬度变化，从而导致天敌逃逸对外来植物入侵成功的影响在大空间尺度上存在异质性。相关研究目前还开展较少。项目以我国沿海重大外来入侵植物互花米草和土著植物芦苇作为研究体系，研究昆虫天敌对二者取食压力的纬度变化差异，并通过野外天敌排除试验，评价昆虫天敌取食对不同纬度互花米草和芦苇生长表现和竞争关系的影响，以揭示天敌逃逸对互花米草入侵成功影响的空间异质性及生态后果。项目还拟通过野外植物特征渐变和昆虫天敌组成变化影响分析，以及同质种植园试验，深入研究互花米草和芦苇植食压力纬度变化背后不同的遗传分化和表型可塑性驱动机制。项目将有助于进一步增进我们对外来植物在生物地理尺度上成功入侵机制的了解，发展和完善相关的生物入侵生态学理论，并对不同纬度地区互花米草的防治和管理工作提供参考。

天敌逃逸在大空间尺度上的异质性对外来植物入侵成功具有重要影响，但相关研究目前还较少。项目通过对我国东部沿海（纬度跨度~20°N）外来入侵植物互花米草Spartina alterniflora和土著植物芦苇Phragmites australis种群的植食压力进行调查，发现二者叶植食损失率存在非平行的纬度分异关系。高纬度地区两种植物的叶植食压力差别最大。通过室内取食和竞争操控试验表明，植食昆虫取食能够显著抑制芦苇对互花米草的竞争影响。上述结果证实了天敌逃逸是导致互花米草成功入侵的重要机制，并且其对互花米草入侵成功的影响具有纬度差异。此外，主成分回归分析表明互花米草叶植食损失率与株高和叶总酚含量显著相关，表明 “土著植食昆虫-互花米草”互作强度的纬度变化，可能与互花米草在入侵地的“生长-防御能量投入”权衡有关。通过同质种植园试验，项目发现互花米草植食相关特征的纬度分异主要受可塑性驱动，而芦苇纬度分异具有遗传基础的特征数量更多。进一步对两种植物上不同昆虫功能群组成的纬度变化进行比较，结果发现互花米草上捕食-寄生昆虫物种数受纬度影响较小，而植食昆虫物种数则在中纬度最高。较弱的天敌-植食昆虫互作强度可能是导致互花米草中纬度植食压力增高的重要原因。为揭示高营养级动态对“土著植食昆虫-互花米草”互作的可能影响，项目通过室内取食试验和野外存活试验数据，证实了互花米草入侵能够对土著植食昆虫素毒蛾Laelia coenosa造成“天敌逃逸空间”，并促进其在互花米草上的种群扩张。上述结果对于互花米草成功入侵机制的阐释，以及生物入侵理论的完善具有重要意义。