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).