Co-occurring Luzula species (Juncaceae) of different ploidies in alpine grasslands of the Eastern Alps exhibit negligible ecological differentiation at small geographic scale

Luzula sect. Luzula is a taxonomically challenging group of angiosperms, whose evolutionary history has been shaped by polyploidy and agmatoploidy (fragmentation of holocentric chromosomes). Several species with different chromosome sizes and numbers, ranging from diploids to hexaploids, occur above timberline in the Eastern Alps. Species of different ploidies frequently co-occur in the same habitats, but the extent of ecological divergence and niche partitioning among them remains elusive, partly due to their high morphological similarity impeding reliable identification. Here, we focused on three mixed-ploidy sites in the Eastern Alps, where morphologically similar alpine species L. exspectata (diploid), L. alpina (tetraploid) and L. multiflora (its hexaploid populations) co-occur. We inferred there ploidy via flow cytometry and characterised their small-scale ecological differentiation using Landolt indicator values of accompanying species that revealed limited ecological divergence between co-occurring ploidies. While diploid L. exspectata is associated with slightly more basophilic microsite conditions, as it mostly occurs over limestone, no such differentiation was observed between tetraploid L. alpina and hexaploid L. multiflora . Our results indicate that small-scale co-occurrence of different cytotypes within Luzula sect. Luzula in alpine habitats is accompanied by only a slight niche partitioning, whereas there were significant differences in ecological parameters among the sites. These findings emphasise the influence of geography and geology on ecological microsite conditions and suggest that local niche divergence between ploidies is negligible compared to site-specific effects. Different ploidies thus likely have more divergent ecology at a distribution-wide scale than at a local scale