ABSTRACT
These topics are relatively well-understood for certain micronutrients, but further investigations are needed for many other trace elements. The reaction of plants to chemical stresses that are caused by both deficiencies and excesses of trace elements cannot be defined exactly because plants have developed during their evolution and course of life (ontogeny and phylogeny) several biochemical mechanisms that have resulted in adaptation to and tolerance of new or chemically imbalanced environments. Therefore, plant responses to trace elements in the soil and ambient air should always be investigated for the particular soil-plant system.
