This paper illustrated the conditions of iron plaque formation on root surface, the morphology, mineralogical composition and deposition site of the plaque, and its function as a Fe reservoir in supplying Fe nutrient and affecting the uptake of other nutrients such as phosphorus and zinc. The environmental and ecological role of the plaque in inhibiting the uptake and translocation of heavy metals such as Cu, Ni, Cd and As through absorption or co-precipitation was called external tolerance mechanism, while its competition with heavy metals for metabolically sensitive sites in plants was called internal tolerance mechanisms. These two mechanisms help plant survive in high acidic and low carbon environment.