Phylogenetic ecology uses evolutionary history to improve understanding of plant interactions. Phylogenetic distance can mediate plant interactions such as competition (e.g., via limiting similarity) and facilitation (e.g., via niche complementarity), influencing community assembly patterns. Previous research has found evidence both for and against a relationship between phylogenetic distance and the strength of plant interactions, and has found that other factors, such as trait differences, may be more influential. In addition to phylogenetic distance and species’ traits, environmental conditions can also influence competition, with facilitative interactions—particularly among distantly related species—potentially becoming more pronounced under stressful, resource-limited conditions. We tested the prediction that greater phylogenetic distance is associated with decreased competition in a greenhouse experiment using plant species of the North American tallgrass prairie. We calculated the Relative Interaction Index for 81 species pairs using plant height, leaf length, and biomass as indicators of performance. We found that phylogenetic distance alone did not significantly affect competition. However, the interaction between phylogenetic distance and stressful conditions (sandier soils with low nutrient availability and water retention vs. resource-rich potting soil) altered plant traits and competition. Under stressful conditions, more distantly related species competed more strongly, leading to smaller plants. Conversely, under benign conditions more distantly related species pairs competed less and were larger. These results were contrary to our expectations that distant relatives would compete less under stressful conditions. Our experiment provides evidence that, while relatedness alone may not drive competition, phylogenetic distance can nonetheless be influential through interactions with environmental conditions.

系统发育生态学使用进化历史来提高对植物相互作用的理解。系统发育距离可以介导植物相互作用，例如竞争（例如，通过限制相似性）和促进（例如，通过生态位互补），影响群落组装模式。先前的研究已经发现了支持和反对系统发育距离与植物相互作用强度之间关系的证据，并发现其他因素，例如性状差异，可能更具影响力。除了系统发育距离和物种特征之外，环境条件也会影响竞争，促进相互作用——尤其是远亲物种之间——在压力大、资源有限的条件下可能变得更加明显。我们在使用北美高草草原植物物种的温室实验中测试了更大的系统发育距离与减少竞争相关的预测。我们使用植物高度、叶长和生物量作为性能指标计算了 81 个物种对的相对相互作用指数。我们发现单独的系统发育距离并没有显着影响竞争。然而，系统发育距离和压力条件（具有低养分可用性和保水性的砂质土壤与资源丰富的盆栽土壤）之间的相互作用改变了植物性状和竞争。在压力条件下，亲缘关系越远的物种竞争越激烈，导致植物变小。相反，在良性条件下，亲缘关系较远的物种对竞争较少且体型更大。这些结果与我们的预期相反，即远亲在压力条件下会减少竞争。我们的实验提供的证据表明，虽然相关性本身可能不会推动竞争，但系统发育距离仍然可以通过与环境条件的相互作用产生影响。