Dunnett test is more stringent than pairwise test

[LLansing]

I've ran the same ancombc2 analysis as both Dunnett and pairwise, but the Dunnett results have fewer significantly differential taxa. My understanding was that the Dunnett test employs fewer comparisons and thus p-value adjustment would make a smaller impact compared to the pairwise results. However, it appears I may be mistaken.

Is my understanding incorrect?

Here are my function calls:

da_sp <- ancombc2(data = species_pseq,
                fix_formula = "trt.foster+rep",
                p_adj_method = "BH",
                n_cl = 4,
                pseudo_sens = TRUE,
                group = "trt.foster",
                pairwise = TRUE)
 
 da_sp_dun <- ancombc2(data = species_pseq,
                   fix_formula = "trt.foster+rep",
                   p_adj_method = "BH",
                   n_cl = 4,
                   pseudo_sens = TRUE,
                   group = "trt.foster",
                   dunnet = TRUE)

to which I then compare the number of values that are TRUE in da_sp$res_pair$diff<comparison> columns to da_sp_dun$res_dunn$diff<comparison> columns.

[Maggie8888]

Dunnett test controls multiple comparisons, you may find helpful information form the website https://en.wikipedia.org/wiki/Dunnett%27s_test