Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant-insect interaction analysis and variance partitioning of biodiversity effects. We present a case-study experiment in which facilitation by a cushion-plant species and a dwarf-shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: 1) removal of plant species associated with ecosystem engineers, 2) exclusion (covering) of ecosystem engineer flowers, and 3) control, i.e. natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity-ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects.

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评估生态系统工程师对生物多样性和生态系统功能影响的实验方法

植物作为生态系统工程师创造栖息地并促进植物群落内的生物多样性维护。此外，生物多样性研究表明，植物多样性提高了生态系统的生产力和功能。然而，这两个研究领域是平行发展的，彼此独立，结果是生态系统工程师在生物多样性和跨营养级生态系统功能之间的关系中的作用知之甚少。在这里，我们提出了一个实验框架来研究这种关系。我们将植物作为生态系统工程师的促进作用与植物-昆虫相互作用分析和生物多样性影响的方差划分相结合。我们提出了一个案例研究实验，其中垫层植物物种和矮灌木物种作为生态系统工程师的促进增加了植物功能多样性（生态系统工程师和相关植物）对生态系统功能（花卉访问率）的积极影响。该实验在单个高山开花季节在田间进行，包括以下处理：1) 去除与生态系统工程相关的植物物种，2) 排除（覆盖）生态系统工程花，以及 3) 控制，即自然斑块生态系统工程师和相关植物物种。我们发现植物之间的正负关联效应取决于生态系统工程师的身份，表明授粉促进和干扰。在这两种情况下，生态系统工程师支持的补丁增加了花卉访客的系统发育和功能多样性。此外，工程师和相关植物之间的互补效应对花卉访问率是积极的。我们的研究表明，植物促进可以增强生物多样性-生态系统功能关系的强度，植物之间的互补性吸引更多和多样化的花卉游客可能是驱动因素。一个潜在的机制是工程师和相关植物之间的协同作用和互补性增加了对共享访客的吸引力并扩大了授粉生态位。综合而言，植物之间的促进可以扩展到一个完整的网络，通过微生境改善直接和通过多样性效应间接支持生态系统功能。