Distribution of Frankia OTUs
Rarefaction curves also illustrated the high diversity of our clone sequences. For unique sequences, curves increased linearly across all levels of sampling effort, suggesting the presence of much greater diversity in our field soils than we managed to detect (Figure S5). When OTUs were aggregated at 99% similarity, however, curves for all soils except early succession strongly saturated, suggesting our sample was likely to have captured nearly all of the 16S-23S IGS diversity available at that level. For clade-based OTUs, the effect was even stronger: of the six treatments/locations we studied, all of our sample sizes were well beyond the inflection point of the OTU accumulation curve, and four of them – late succession alder and non-alder, and mid-succession N and P – appear to be well into the asymptotic portion of the curve (Figure 2). The two exceptions – early succession and mid-succession unfertilized – were only modestly increasing in the extrapolation portion of the curve (Figure 2).