Time course of plant diversity effects on Centaurea jacea establishment and the role of competition and herbivory

Aims Invasion resistance in experimental plant communities is known to increase with increasing diversity and further to depend on the presence of particular functional groups.To test whether these effects also hold true for the invader establishment phase beyond the seedling stage,we studied survival and performance of Centaurea jacea L.(brown knapweed)planted into experimental grassland communities of varying plant biodiversity over three consecutive years.Moreover,we analysed the role of insect herbivory and biomass of the recipient community for mediating diversity effects.Methods In 2005,seedlings of Centaurea were transplanted into experimental grassland communities(the Jena Experiment)covering a species richness(1–60)and functional group richness(1–4)gradient.Half of these transplants and the community surrounding them in each plot were sprayed with insecticide while the other half served as control.In 2006 and 2007(during the second and third year after transplantation),we recorded survival,growth-related(e.g.transplant biomass,height)and reproduction-related traits(e.g.number of flower heads).Annual data on community aboveground biomass served as covariate to investigate mediating effects of aboveground competition with the recipient community.Important Findings Species richness was the most important factor responsible for Centaurea limitation.Higher levels of diversity decreased survival and all performance traits in both years.These diversity effects were partly driven by community biomass,but not fully explained by that covariate,suggesting the importance also of further processes.The influence of functional group richnesswas strong in the second year after transplantation and weaker in the third year.Among the particular functional groups,only the presence of legumes showed strong negative effects on Centaurea survival and weak negative effects on growth and reproduction,the latter two being mediated by biomass.Insect herbivore reduction considerably benefited Centaurea in sprayed monocultures,where it grew significantly larger than in all other diversity levels and than in the control subplots.We conclude that effects of plant community properties on invading individuals change in the course of establishment,that plant species richness effects are also important during later stages of establishment,and that biomass(especially at high diversity)and herbivory(especially at low diversity)of the recipient community are important in mediating community effects on invaders.

棕色矢车菊在我国的适生区预测与入侵风险评估

棕色矢车菊是原产欧洲的恶性杂草,近年来我国从进口粮谷中截获其种子。为了评估棕色矢车菊入侵我国的潜在适生区及入侵风险,我们首先采用MaxEnt生态位模型预测该杂草在我国的适生区;其次,采用层次分析法构建其入侵的综合风险评估指标体系,定量评估入侵我国的综合风险。结果表明棕色矢车菊在我国的适生区广泛,综合风险值为0.85,属高风险等级。建议加强进境检疫管理,尽快开展系统监测并构建早期监测预警网络。