Data from: The reciprocal relationship between competition and intraspecific trait variation

Trait differences among plants are expected to influence the outcome of competition; competition should be strongest between similar species (or individuals) under limiting similarity, and between dissimilar species within competitive hierarchies. These hypotheses are often used to infer competitive dynamics from trait patterns within communities. However, plant traits are frequently plastic in response to competition. This variation is poorly accounted for in trait based studies of competition and community assembly. To explore the relationship between trait responses and competitive outcomes, we grew 15 species alone, in monoculture, and in mixture. We measured traits relating to leaf and root tissue morphology as well as biomass allocation and related competition induced changes in these traits to intra- and interspecific competition using multi-model inference. Additionally, we tested how traits from different competitive environments influenced potential community assembly inferences. The competitive environment had large effects on species’ traits, although many effects were species-specific. Differences among species in how competition affected trait expression was linked to both intra- and interspecific competition, frequently affecting competitive hierarchies. Intraspecific competition was lower for species that limited competition-induced increases in root allocation and had less variability in this trait overall. Interspecific competition was lower for species with larger leaves and lower specific leaf area than their neighbours. Switching to more stress tolerant strategies by increasing root diameter and leaf tissue density also reduced competition. However, dissimilarity in root tissue density also minimized competition, consistent with limiting similarity affecting competitive outcomes. Moreover, changes in these traits were linked to changes in functional diversity, suggesting that competition affects functional diversity by affecting trait expression. Synthesis – Both trait hierarchies and trait dissimilarity affect the outcome of competition by acting on different traits, although competition-induced changes in trait expression can alter the outcome. Moreover, the magnitude of these trait changes suggests that the source environment where plant traits are collected can affect the inferences drawn from trait patterns within communities. Combined, our results suggest that considering the effect of competition on trait expression is critical to understanding the relationship between traits and community assembly.

植物的性状差异本应会影响竞争结局；依据极限相似性（limiting similarity）假说，性状相似的物种（或个体）间竞争强度最高，而在竞争等级（competitive hierarchies）体系内，性状差异较大的物种间竞争则更为激烈。这类假说常被用于通过群落内的性状分布格局推断群落中的竞争动态。然而，植物性状常会因竞争产生表型可塑性，而在基于性状的竞争与群落构建研究中，这类性状变异常未得到充分考量。为探究性状响应与竞争结局间的关联，本研究将15个物种分别以单株、单种纯培、多物种混培三种方式进行种植。我们测定了与叶片、根系组织形态及生物量分配相关的性状，并通过多模型推断（multi-model inference）将这些性状中竞争诱导产生的变化与种内、种间竞争建立关联。此外，本研究还检验了不同竞争环境下获取的性状，会如何影响基于群落构建的相关推断。竞争环境对物种性状具有显著影响，但多数影响具有物种特异性。不同物种在竞争对其性状表达的调控方式上存在差异，这种差异与种内、种间竞争均存在关联，且常会改变群落的竞争等级格局。对于能够抑制竞争诱导的根系生物量分配增加、且该性状整体变异度更低的物种，其种内竞争强度更低。相较于邻物种，拥有更大叶片与更低比叶面积（specific leaf area, SLA）的物种，其种间竞争强度更低。通过增大根系直径、提升叶片组织密度以转向更耐胁迫的生存策略，同样可降低竞争强度。不过，根系组织密度的性状差异同样会弱化竞争强度，这与极限相似性假说中性状差异影响竞争结局的论断相符。此外，这些性状的变化与功能多样性（functional diversity）的改变存在关联，这表明竞争可通过调控性状表达来影响群落功能多样性。综合结论：性状等级与性状差异均通过作用于不同性状来影响竞争结局，但竞争诱导的性状表达变化同样可能改变竞争结局。此外，这些性状变化的幅度表明，植物性状的采集源环境会影响基于群落内性状分布格局所得到的推断结果。综合来看，本研究结果表明，若要厘清性状与群落构建间的内在关联，考量竞争对性状表达的影响至关重要。