Department of Ecology and IMEM, University of Alicante, Alicante, Spain.
Mediterranean Center for Environmental Studies (CEAM Foundation), Joint Research Unit University of Alicante-CEAM, University of Alicante, Alicante, Spain.
PLoS One. 2019 Aug 23;14(8):e0221667. doi: 10.1371/journal.pone.0221667. eCollection 2019.
Competition is a major factor structuring plant communities and controlling their productivity. The functional similarity between the interacting species and the context resource availability are assumed to be most critical factors that modulate the strength, sign, and outcome of plant competition, yet their roles and interactions are subjected to debate. In a glasshouse experiment, we constructed monocultures and bi-specific cultures of three common perennial grasses of Mediterranean drylands, the short grass Brachypodium retusum and the tussock grasses Stipa tenacissima and Lygeum spartum, and investigated how the functional similarity between these species modulate their interactions and culture productivity under contrasting levels of water availability. Regardless the degree of functional similarity between the interacting species, B. retusum consistently exhibited a greater competitive ability than the other two species, followed by L. spartum, and with S. tenacissima behaving as the weakest competitor. Bi-specific cultures of B. retusum and either L. spartum or S. tenacissima produced higher biomass than the average biomass of the respective monocultures (i.e. overyielding), whereas the combination of the most similar species, L. spartum-S. tenacissima, which exhibited the highest competition symmetry (i.e., the more similar mutual impact), did not show any significant overyielding. Higher water availability increased productivity and promoted transgressive overyielding for the most dissimilar species, B. retusum and L. spartum, which however exhibited intermediate competition asymmetry. This study calls attention to the thin line between differences in functional traits and competition asymmetry that could eventually lead to either competitive exclusion or resource partitioning and coexistence.
竞争是构建植物群落和控制其生产力的主要因素。相互作用的物种之间的功能相似性和资源可利用性是调节植物竞争强度、方向和结果的最关键因素，但它们的作用和相互关系仍存在争议。在温室实验中，我们构建了三种常见地中海干旱地区多年生草本植物的单种和双种培养物，短草 Brachypodium retusum 和丛生草 Stipa tenacissima 和 Lygeum spartum，并研究了这些物种之间的功能相似性如何在不同的水分可利用度水平下调节它们的相互作用和培养物生产力。无论相互作用的物种之间的功能相似性程度如何，Brachypodium retusum 始终表现出比其他两种物种更强的竞争能力，其次是 Lygeum spartum，而 Stipa tenacissima 则表现出最弱的竞争力。Brachypodium retusum 与 Lygeum spartum 或 Stipa tenacissima 的双种培养物比各自的单种培养物产生更高的生物量（即超产量），而最相似的物种（即 Lygeum spartum-S. tenacissima）的组合，表现出最高的竞争对称性（即相互影响越相似），并没有表现出任何显著的超产量。较高的水分可利用度增加了生产力，并促进了最不相似的物种（Brachypodium retusum 和 Lygeum spartum）的过度产量，然而，这两个物种表现出中等的竞争不对称性。这项研究提醒人们注意功能性状和竞争不对称性之间的细微差别，这最终可能导致竞争排斥或资源分配和共存。
