Manganese (Mn) availability in soil and its function in plant metabolism
KEY FACTS
- Manganese is the second most abundant trace element (after iron) in the Earth’s crust.
- Mn is a relatively immobile element in the plant.
- Mn plays a critical role in regulating redox processes and photosynthesis efficiency.
- Cereals are particularly susceptible to manganese deficiency; yield losses of up to 30-60 percent can occur in severe Mn deficiency.
- Soil-applied manganese can be rapidly fixed or converted to unavailable forms — thus, foliar applications are usually recommended
FUNCTION
- Important role in photosynthesis – catalyst of water hydrolysis
- Activator of enzymes involved in plant metabolism, including chlorophyll synthesis
- Involved in decarboxylation and free nitrogen binding processes (legume species)
- Facilitates plant absorption of potassium and regulates it
- Role in the neutralization of reactive oxygen species (ROS)
- Manganese imbalances are often a causative factors of fungal and bacterial infestations.
AVAILABILITY
- Most Mn is present in forms that are not available for plant uptake.
- The total amount of manganese in soils is around 0.25 percent but can reach as high level as 13 percent in some volcanic soils.
- Manganese availability decreases as the pH increases (above a pH of 7.5, Mn availability is usually not adequate for plant demands); below 5.5, Mn becomes very soluble and toxicity symptoms may occur.
- Mn ions form complexes with organic matter in alkaline soils that are high in organic matter.
- High concentrations of other cations in the soil solution (e.g., calcium, zinc, iron, magnesium and ammonium) may reduce Mn uptake.
- Exchangeable manganese in the soil differs significantly depending on seasonal conditions:
- Cold and wet conditions may induce deficiency due to the combined effect of reduced mineralization of soil organic matter, reduced root growth and Mn uptake rate.
- In water-logged conditions, insoluble manganese oxide can be reduced by soil bacteria to Mn2+, resulting in temporal toxicity.
- In dry soil conditions, insoluble Mn salts can form in the soil, reducing the availability of Mn.
Credits: Michał Słota Ph.D., Content Farmers.
