Comparing soil mesofauna communities using large-scale DNA sequencing

We are studying soil mesofauna community structure using large-scale sequencing of 18S rDNA from the Arctic to the Antarctic.  This study reports the results obtained from La Selva, Costa Rica and the Toolik Lake LTER, Alaska.  At each site a 900m transect was established comprised of 4 evenly spaced plots (10 x10 m). Twenty soil cores were combined from each plot and separated into three size fractions (1-2mm, 1-0.5mm 0.5-0.05), and 18S rDNA was extracted. Based on 99%, 97% and 95% minimum matching percentage, we assigned 254, 131 and 86 OTUs  (operational taxonomic units) from 2552 Costa Rican sequences, of which 81%, 76% and 70% were singletons, respectively.  In the Alaska Toolik samples, the total OTUs were 308, 155, and 114 from 2646 sequences and the percentage of the singletons was 71%, 63% and 57% respectively. Using the Bray-Curtis similarity index we found no difference between plots or screen size within sites, however, the Costa Rican and Alaskan communities were different. Hierarchical clustering and non-metric multidimensional scaling (MDS) methods showed less than 10% similarity in OTUs between the Costa Rican and Alaskan locations. As sequence data from other locations are analyzed, this study will provide insight into global patterns of soil biodiversity.