The same thing, in my opinion, may be true about 'absorb', but in this case the original language is Latin and the receptive language is Polish.
If you're sure that 'absorb' is a root in Polish, then it can be used as a meaningful morpheme.
I think it is a root in the light of what you say! Take a look at a couple of examples I'm going to provide.
Also I think I have to change my mind again regarding the morphemes in the word "absorbować". I'm unsure what the actual meaning of the interfix "-owa-" is! I said it's a verb-making affix. But as you noticed, I wasn't entirely sure about it. I'm even less sure now.
absorb - owa - ć = to absorb (infinitive)
absorb - owa - nie = absorbing (gerund)
absorb - owa - łem = I absorbed (in the past)
absorb - owa - ły = they absorbed (in the past)
absorb - owa - ny = absorbed (passive adjectival participle)
absorb - owa -wszy = having absorbed (past adverbial participle)
absorb - uj - ę = I'm absorbing or I absorb (present tenses)
absorb - uj - ą = they're absorbing or they absorb (present tenses)
absorb - uj - ący = absorbing (active adjectival participle)
absorb - uj - ąc = absorbing (present adverbial participle)
As you can see, two verb-making affixes ("-owa-" and "-uj-") are applied to the root "absorb" depending on the grammatical form of the verb that we want to create! "-owa-" seems mostly past and "-uj-" seems present. But I can't be sure about it... It's just what I'm finding out about my language at this very moment!
PS: I think I understand the problem now. In your diagrams, every vertex of the tree that is not an affix must be a word! I think it doesn't apply to Polish... Let's take the word "szafa", which means wardrobe in Polish. Let's write down all the singular cases of the word:
szaf - a (nominative)
szaf - y (genitive)
szaf - ie (dative)
szaf - ę (accusative)
szaf - ą (instrumental)
szaf - ie (locative)
szaf - o (vocative)
I think it's clear that "szaf-" is the root here. But "szaf" is not a word!
PPS: OK, it is a word but it's an accident! It's the plural genitive!