Ammonium (NH4+) toxicity is an issue of global ecological and economic importance. In this
review, we discuss the major themes of NH4+ toxicity, including the occurrence of NH4+ in
the biosphere, response differences to NH4+ nutrition among wild and domesticated
species, symptoms and proposed mechanisms underlying toxicity, and means by which it
can be alleviated. Where possible, nitrate (NO3−) nutrition is used as point of comparison.
Particular emphasis is placed on issues of cellular pH, ionic balance, relationships with …