i was keeping a pair of convicts in my tank, so i was told by a freind who seemed to know his stuff that salt is good for the fish, but would have little effect on the plants. i added it and the fish thrived while the plants showed no adveres reaction. before that, i had kept them with a pleco and a salvani without salt in my tank and they did fine with the plants thriving under the same conditions as when i began to add salt. therefore, overall i could see no harmful effects to usuage of salt to going without it. now i keep a mated pair of mollies and they like salt, so i add it regularly. the plants, anubias, java fern and amazons, still thrive and i have to cut my prize sword every 8 weeks as always.
i guess what im saying that in my experience i have never seen the plants react adversely to adding salt to the water. hope that helps.