Grassland above and below ground community shift across soil moisture transition

Since Linnaeus's time, the Kungsängen Nature Reserve has drawn frequent visitors because of its vegetation including the largest population of Fritillaria meleagris L. in Sweden. The reserve is a meadow with an abrupt moisture transition, where the wetter part has a Carex acuta dominated plant community with low species richness, visually distinct from the drier part, which has a species rich plant community including a high density of Fritillaria meleagris. To investigate the link between plant and below-ground micro-eukaryotic communities, we amplified and sequenced the ITS and LSU regions of the rDNA operon (1500 bp) from soil using PacBio SMRT sequencing, and evaluated three different methods for generation of operational taxonomic units. We found distinct communities associated with wet and mesic-dry soil conditions but estimated richness was not so different. Both soil conditions host communities dominated by protists, a large fraction of which were taxonomically assigned to Ciliphora (Alveolata), while 30-40% of all reads were assigned to kingdom Fungi. Ecological patterns were consistently recovered irrespective of the read clustering method used. However, different clustering methods affect the taxonomic and phylogenetic resolution of community characterization with implications for how well members of the micro-eukaryotic communities can be recognized in the data.