Data from: The strength of negative plant-soil feedback increases from the intraspecific to the interspecific and the functional group level

1. One of the processes that may play a key role in plant species coexistence and ecosystem functioning is plant-soil feedback, the effect of plants on associated soil communities and the resulting feedback on plant performance. Plant-soil feedback at the interspecific level (comparing growth on own soil with growth on soil from different species) has been studied extensively, while plant-soil feedback at the intraspecific level (comparing growth on own soil with growth on soil from different accessions within a species) has only recently gained attention. Very few studies have investigated the direction and strength of feedback among different taxonomic levels, and initial results have been inconclusive, discussing phylogeny and morphology as possible determinants. 2. To test our hypotheses that the strength of negative feedback on plant performance increases with increasing taxonomic level and that this relationship is explained by morphological similarities, we conducted a greenhouse experiment using species assigned to three taxonomic levels (intraspecific, interspecific and functional group level). We measured certain fitness-related aboveground traits and used them along literature-derived traits to determine the influence of morphological similarities on the strength and direction of the feedback. 3. We found that the average strength of negative feedback increased from the intraspecific over the interspecific to the functional group level. However, individual accessions and species differed in the direction and strength of the feedback. None of our results could be explained by morphological dissimilarities or individual traits. 4. Synthesis. Our results indicate that negative plant-soil feedback is stronger if the involved plants belong to more distantly related species. We conclude that the taxonomic level is an important factor in the maintenance of plant coexistence with plant-soil feedback as a potential stabilizing mechanism and should be addressed explicitly in coexistence research, while the traits considered here seem to play a minor role.

1. 在植物物种共存与生态系统功能维持中，发挥关键作用的核心过程之一是植物-土壤反馈（plant-soil feedback）——即植物对其关联土壤群落的调控作用，以及由此产生的对植物自身生长表现的反馈效应。目前学界已对种间水平（interspecific level，即比较植物在自源土壤与异种来源土壤上的生长差异）的植物-土壤反馈开展了大量研究，但种内水平（intraspecific level，即比较植物在自源土壤与同物种内不同种质来源土壤上的生长差异）的相关研究直至近年才受到关注。现有研究中，针对不同分类学水平下反馈的方向与强度的探讨极少，且初期结果尚无定论，研究者多将系统发育与形态特征视为潜在的决定因素。
2. 为验证两项假说：其一，植物生长表现所受负反馈的强度随分类学水平提升而增强；其二，该关联可由形态相似性解释，我们开展了温室控制实验，将研究物种划分为三类分类学水平：种内水平、种间水平与功能群水平。我们测定了若干与适合度相关的地上部性状，并结合文献来源的性状数据，探究形态相似性对植物-土壤反馈强度与方向的影响。
3. 研究结果显示，负反馈的平均强度从种内水平、种间水平到功能群水平依次递增。但单个种质与物种的反馈方向与强度存在显著异质性。本研究所有结果均无法通过形态差异或单个性状得到解释。
4. 研究总结。我们的结果表明，当参与交互的植物亲缘关系越远时，其负向植物-土壤反馈作用越强。综上，分类学水平是维持植物物种共存的重要因素，植物-土壤反馈可作为潜在的稳定机制，该因素应在物种共存研究中得到明确关注；而本研究涉及的性状对反馈的影响相对较小。