Trophic and non-trophic interactions influence the mechanisms underlying biodiversity–ecosystem functioning relationships under different abiotic conditions

Plant diversity effects on ecosystem functioning usually have been studied from a plant perspective. However, the mechanisms underlying biodiversity–ecosystem functioning relationships may also depend on positive or negative interactions between plants and other biotic and abiotic factors, which remain poorly understood. Here we assessed whether plant–herbivore and/or plant–detritivore interactions modify the biodiversity–ecosystem functioning relationship and the mechanisms underlying biodiversity effects, including complementarity and selection effects, biomass allocation, vertical distribution of roots, and plant survival using a microcosm experiment. We also evaluated to what extent trophic and non-trophic interactions are affected by abiotic conditions by studying drought effects. Our results show that biotic and abiotic conditions influence the shape of the biodiversity–ecosystem function relationship, varying from hump-shaped to linear. For instance, total biomass increased linearly with plant richness in the presence of detritivores, but not in the absence of detritivores. Moreover, detritivore effects on belowground plant productivity were highly context dependent, varying in the presence of herbivores. Plant interactions with soil biota, especially with herbivores, influenced the mechanisms underlying diversity effects. Herbivores increased plant complementarity and modified biomass allocation and vertical distribution of roots. Furthermore, biotic–abiotic interactions influenced plant productivity differently across plant functional groups. Our findings emphasize the importance of complex biotic interactions underlying biodiversity effects, and that these biotic interactions may change with abiotic conditions. Despite minor changes in productivity in the short-term, soil biota-induced changes in plant–plant interactions and plant survival are likely to have significant long-term consequences for ecosystem functioning. Considering the context-dependency of multichannel interactions may contribute to reconciling differences among observed patterns in biodiversity studies. Further, abiotic conditions modified the effects of biotic interactions, suggesting that changes in environmental conditions may not only affect ecosystems directly, but also change the biotic composition of and dynamics within ecosystems.植物多样性对生态系统功能的影响，过往研究通常仅从植物自身视角展开。然而，生物多样性-生态系统功能关系（biodiversity–ecosystem functioning relationships）背后的潜在机制，可能同样取决于植物与其他生物、非生物因子间的正负相互作用，而这类作用的相关认知仍较为匮乏。本研究借助微宇宙实验（microcosm experiment），探究植物-草食动物、植物-腐食动物的相互作用是否会改变生物多样性-生态系统功能关系，以及生物多样性效应背后的潜在机制——包括互补效应与选择效应（complementarity and selection effects）、生物量分配、根系垂直分布以及植物存活情况。本研究同时通过探究干旱效应，评估了非生物条件对营养级与非营养级相互作用的影响程度。研究结果表明，生物与非生物条件会影响生物多样性-生态系统功能关系的形态，其形态可从驼峰型转变为线性。例如，在腐食动物存在的情况下，总生物量随植物丰富度呈线性增长，而在腐食动物缺失时则无此现象。此外，腐食动物对地下植物生产力的影响具有极强的情境依赖性，且会随草食动物的存在与否发生变化。植物与土壤生物群（soil biota）的相互作用，尤其是与草食动物的相互作用，会影响多样性效应背后的潜在机制。草食动物会增强植物的互补效应，并改变生物量分配与根系垂直分布。此外，生物-非生物相互作用对植物生产力的影响，因植物功能群（plant functional groups）的不同而存在差异。本研究结果凸显了生物多样性效应背后复杂生物相互作用的重要性，且这类生物相互作用会随非生物条件的变化而改变。尽管短期内植物生产力仅发生小幅变化，但土壤生物群介导的植物间相互作用与植物存活的改变，可能会对生态系统功能产生深远的长期影响。考虑到多渠道相互作用的情境依赖性，或有助于调和生物多样性研究中观测到的不同模式间的差异。进一步而言，非生物条件会改变生物相互作用的效应，这表明环境条件的变化不仅会直接影响生态系统，还会改变生态系统内的生物组成与动态。