Are mushrooms obligated in terumos and maaser?
They are not obligated, even though they might appear as if they were planted on the ground, they grow from the air. As a side point, mushrooms sold in cans in Israel, are not grown locally, but in Holland and other countries, where terumos u’ma’asros are not applicable.
Kesiva vchasima tova
Rambam Terumos 2-1, Shevet Halevi 8-248.