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...