In all languages: if there are non-root morphemes, then all such morphemes have a more limited inventory of phonemes than root-morphemes and the average length of non-root morphemes is not more than the length of root-morphemes.
Standardized
Provided there are non-root as well as root morphemes, non-root morphemes have a more limited inventory of phonemes than root-morphemes and are on average shorter than root-morphemes.
Not entirely equivalent:IF phonemes can occur in non-root morphemes, THEN they can also occur in root-morphemes.For example, non-roots may have a very limited set of vowels, whereas roots may use all vowels; but there may be non-root vowels (e.g. schwa) that cannot occur in roots.IF non-roots can be x long (x measured in segments, syllables, moras …), THEN roots will on average be longer than x.
Not entirely equivalent:IF phonemes can occur in non-root morphemes, THEN they can also occur in root-morphemes.For example, non-roots may have a very limited set of vowels, whereas roots may use all vowels; but there may be non-root vowels (e.g. schwa) that cannot occur in roots.IF non-roots can be x long (x measured in segments, syllables, moras …), THEN roots will on average be longer than x.