MANGANESE TOXICITY IN PLANTS

Manganese (Mn) toxicity in plants is often not a clearly identifiable disorder. Symptoms of Mn toxicity as well as the concentration of Mn t hat causes toxicity vary widely among plant species and varieties with in species, perhaps because the phytotoxic mechanisms of Mn involve di fferent biochemical pathways in different plant genotypes. Plant avail ability of Mn depends on soil adsorption and on root exudates for Mn c helation or reduction. Soils with higher Mn sorption capacity have low er potential for plant absorption of Mn. Great Mn tolerance is associa ted with restricted absorption, restricted translocation of excess Mn to the shoots, or great tolerance to high Mn levels within the plant t issue. The ability to escape Mn toxicity through limited absorption or translocation is low in plants grown in wet soils rich in organic mat ter, or grown under high temperature or high light intensity. Manganes e toxicity is likely with plants that are fertilized with acid-forming fertilizers, high rates of superphosphate, or nitrate (NO3-) as sourc e of nitrogen (N), or plants that are low in silicon (Si) or deficient in calcium (Ca), iron (Fe), magnesium (Mg), or phosphorus (P). Compar ative studies of Mn toxicity among different genotypes of the same spe cies and a multidisciplinary approach are needed for a full understand ing of Mn toxicity disorder in plants.