Data from: No influence of water limitation on the outcome of competition between diploid and tetraploid Chamerion angustifolium (Onagraceae)

1. Polyploid plants often occupy different geographic ranges than their diploid progenitors, but the causes of this segregation are poorly understood. Differential competitive abilities of cytotypes across an environmental gradient could be responsible for these observed geographic range differences. 2. Cytotypes of Chamerion angustifolium (Onagraceae) are mostly allopatric, and prior research indicates that tetraploids are more physiologically tolerant of water limitation and occupy drier habitats than diploids. We hypothesized that tetraploids are stronger competitors than diploids in soils where water is limited, which allows them to persist in dry habitats while diploids cannot. 3. We grew both cytotypes together in competition under water-limited and well-watered conditions. We varied both total plant density and the relative frequency of cytotypes among pots, which allowed us to separate the effects of intra-cytotypic and inter-cytotypic competition. 4. Both diploid and tetraploid plants were smaller in the water-limited treatment than in the well-watered treatment. Nevertheless, there were no differences in the relative strength of intra-cytotypic and inter-cytotypic competition experienced by either cytotype across the watering treatments, indicating that diploids and tetraploids had equal competitive abilities in both treatments. 5. Synthesis. Competition for limiting resources is often proposed as a mechanism causing ecological and geographic segregation between diploid and polyploid cytotypes. Our results do not support the hypothesis that tetraploid Chamerion angustifolium plants are stronger competitors than diploids when water is limited. A differential ability to compete for water is likely not responsible for the observed ecological and geographic segregation between cytotypes in this species. Competition may not be a general mechanism that causes segregation between diploid and polyploid cytotypes in nature.

1. 多倍体植物（polyploid plants）通常与其二倍体祖先（diploid progenitors）占据不同的地理分布范围，但这种分布分隔的成因仍不甚明晰。不同细胞型（cytotype）沿环境梯度的竞争能力差异，或可解释观测到的地理分布差异。
2. 柳兰（Chamerion angustifolium，柳叶菜科Onagraceae）的细胞型大多呈异域分布，既往研究表明，四倍体（tetraploid）细胞型比二倍体（diploid）细胞型对水分受限的生理耐受性更强，且多栖息于更为干旱的生境。我们提出假说：在水分受限的土壤中，四倍体细胞型的竞争能力强于二倍体细胞型，这使得四倍体能够在干旱生境中存续，而二倍体则无法做到。
3. 我们在水分受限与水分充足两种实验条件下，将两种细胞型共同种植以开展竞争实验。我们通过调控花盆中的总植株密度与细胞型相对频率，得以区分同细胞型竞争（intra-cytotypic competition）与异细胞型竞争（inter-cytotypic competition）的效应。
4. 水分受限处理组中的二倍体与四倍体植株，其个体大小均低于水分充足处理组。然而，两种细胞型在两种水分条件下所经历的同细胞型竞争与异细胞型竞争的相对强度均无显著差异，表明二倍体与四倍体在两种水分条件下的竞争能力相当。
5. 综合与结论。有限资源的竞争常被认为是导致二倍体与多倍体细胞型产生生态与地理分隔的潜在机制。本研究结果并不支持“水分受限条件下柳兰四倍体细胞型的竞争能力强于二倍体细胞型”这一假说。对于该物种而言，水分竞争能力的差异或许并非造成其不同细胞型间生态与地理分隔的原因。在自然生态系统中，竞争或许并非普遍导致二倍体与多倍体细胞型产生分隔的机制。