Hello QIIMEers,
I'm staring at Pvalues and starting to question my own sanity. If someone out there can doublecheck the following interpretations I'd be very grateful!
The Experiment: I have microbiome data from an Icelandic glacial foreland. I've collected samples across three years (one collection per year, yearCollected). Those samples come from 5 age ranges in the foreland (how long that part of the land has been free of glacial ice, iceFreeYears).
I'm currently focusing on teasing out any differences based on the year the data was collected, since that seems to be a large driver of the dataset. To that end, I've done PERMANOVA, PERMDISP and ADONIS with both weighted and unweighted unifraq. Here are the pvalue results:
Weighted Unifraq:

Significance results for yearCollected: PERMANOVA 0.001 PERMDISP 0.003

Signigicance results for iceFreeYears: PERMANOVA 0.042 PERMDISP 0.874

ADONIS formula yearCollected+iceFreeYears: yearCollected 0.001; iceFreeYears 0.16

ADONIS formula yearCollected*iceFreeYears: yearCollected: 0.001; iceFreeYears 0.187; yearCollected:iceFreeYears 0.755
Unweighted Unifraq:

Significance results for yearCollected: PERMANOVA 0.001 PERMDISP 0.064

Signigicance results for iceFreeYears: PERMANOVA 0.007 PERMDISP 0.912

ADONIS formula yearCollected+iceFreeYears: yearCollected 0.001; iceFreeYears 0.032

ADONIS formula yearCollected*iceFreeYears: yearCollected: 0.001; iceFreeYears 0.038; yearCollected:iceFreeYears 0.381
My interpretations:

When looking at total ASVs (unweighted Unifraq), iceFreeYears and yearCollected have different centroids (based on significant pvale of the PERMANOVA), but neither are different enough to be statistically significant (based on nonsignificant pvalue from PERMDISP).

When looking at most abundant organisms (weighted Unifraq), iceFreeYears and yearCollected have different centroids (based on significant pvale of the PERMANOVA), but yearCollected is statistically significant (based on significant pvalue from PERMDISP).

ADONIS of total ASVs (unweighted Unifraq) shows that after partitioning out yearCollected, iceFreeYears is significant, but there's no significant interaction between yearCollected and iceFreeYears ?? (the yearCollected*iceFreeYears values). (this is where I'm getting turned around the most, hence the ??)

ADONIS of the common ASVs (weighted Unifraq) shows that after partitioning out yearCollected, iceFreeYears is NOT significant, and there's no significant interaction between yearCollected and iceFreeYears ?? (the yearCollected*iceFreeYears values).
I've gone through many forum posts to get this far, thanks to everyone who has worked through similar questions with their own datasets. I am going through this data all alone and simply need someone else to tell me if my interpretations make sense (or where I went wrong!) given the test results.
Thank you!