Board Thread:Naruto Discussions/@comment-44437908-20200710093820/@comment-31715856-20200710162940

Pretty sure the reason Yang chakra stimulates Wood Style is because yang's whole shtick is to alter living things (like Calorie Control altering fat and muscle cells, and most likely Medical Ninjutsu too). I don't think it makes sense to say Yang is used by Hashirama for his Wood Style at all. That would be a Kekkei Tota, and we know Wood is Kekkei Genkai. Yamato's wood is weaker and looks more artificial for symbolic reasons (his possession of Hashirama's DNA is not natural) and 1 in-universe reason: His chakra is weaker than Hashirama's. Vastly weaker.

Also, everyone can use Yin and Yang, or at least the basis of using them, according to the databooks. But as Tau said, these aren't elements, and aren't really involved in elemental Kekkei Genkai (Attack of the Twin Demons and Kimmimaro's Kekkei Genkai are probably Yang Style though).