Remember, if your filters are working properly, your tank does NOT contain ammonia. It instead contains Nitrate. The principle reason for doing PWC is to remove some of the Nitrate that builds up over time. Nitrate is a fertilizer, so your plants should love the water.
As for additives we place in a tank... well plants are generally much more hardy any animals, and since our animals are swimming in this stuff, I doubt it could do any harm to plants. The only possible exception might be for those that add salt to their tanks.
In any case, just remember the nitrogen cycle. You add fish food to the tank, the fish convert it to ammonia, bacteria convert the ammonia to nitrite and bacteria convert the nitrite to nitrate, and the plants feed off the nitrate.