Microbial Mediated Micronutrient

Transformation in soil

Fe

Zn

Cu

Mo

Mn

• Plants require some elements in such minute or smaller amounts that these element have been designated as minor/trace element or Micro nutrient.

• Plants absorbed micronutrient in lower concentration ppm level.

Micronutrient

Iron, Zinc, Copper, Manganese, Boron, Molybdenum, Nickel, Chloride

• Source- Goethite, Haematite, Magnetite, Limonite, Olivine

• Forms of Fe- Ferrous & Ferric (Two oxidation state)• Two fraction- Organic & mineral

• Sufficient range of Fe in plants : 50 – 250 ppm.

• Below 50 ppm – Deficiency appears young leaves- Interveinal chlorosis.

• Above 250 ppm- Leaf bronzing.

Iron (Fe)

Fe in soilMineral Fe• 4th most abundant element in earth crust 5%• Solubility is low.

Soil solution• Well drained , oxidised soil has a more Fe3+

• Water logged soil – More Fe2+

Iron bacteria (micro organisms) play a major role

in transformation

Bacteria & fungi oxidise ferrous state to ferric

state.

Heterotrophic microorganism attacks soluble

organic Fe in to inorganic Fe salts.

Bacteria & fungi produce specific enzyme.

Transformation of iron in soil by Micro organisms

Bacteria oxidise ferrous Fe to ferric Fe state which precipitate as ferric hydroxide – Iron Bacteria

• Gallinonella• Siderocapsa• Siderosphaera• Ferribacterium• Naumanniela• Sideromonas• Ferro-bacillus• Siderobacter• Siderococus

• Obligate Chemoautotrophs- Capable of utilizing energy released in the process of ferric hydroxide formation.

(E.g) Gallionella ferruginea

Thiobacillus ferroxidans

Ferrobacillus ferroxidans

Classification

• Facultative Chemoautotrophs-Utilizing energy derived in the process of ferric hydroxide formation or from organic matter.

• (E,g) Leptothrix ochraceae

• Heterotrophs- Do not energy derived in the process of ferric hydroxide formation but depend on organic matter for nutrition.

• (E.g) Naumanniela

• Cyanophycea

• Volvocales

• Chlorococcales

• Eugleninaea

• Conjugales

Transform ferrous salts to ferric salt

Algae

• Source: Limestone, Sandstone.• Forms: Zn2+

• Sufficient range of Zn in plants : 25 – 150 ppm

• Mineral: Zn in lithosphere is 80 ppm• Soil solution: Depends on the soil pH . If pH is

more

Zn2+ availability is more.

Zinc (Zn)

Two fraction

Organic- Small amount 0.01%- 0.05%Inorganic- Source is Zinc sulphate- soluble in soil

Below and above the range cause Rosetting or clustering of young leaves.

Young leaves become chlorotic spot.

• Omnipotent bacteria- Increase concentration of Zn • Fungi also influence solubilize the mineral

from of Zn in soil by production of organic acids.

• Organic material increase the availability of micro organisms in soil

• Increase the availability of Zn in soil

Transformation of Zinc in soil by Micro organisms

• Several zinc solubilizing bacteria (ZSB)- Tropical and temperate soils to provide plant available Zn. (Hafeez et al., 2013).• Gluconacetobacter – sugarcane. • Bacillus, Pseudomonas - Soybean, rice

and wheat capable of solubilizing Zn. (Saravanan et al., 2011).

Omnipotent bacteria

Zinc solubilizing bacteria

•Pseudomonas

•Bacillus

•Gluconacetobacter

•Burkholderia

•Acinetobacter

•Serratia

• Flavobacter

• Enterobacter

Comparison• ZSB• ZSB soil bacteria, able to solubilize the inorganic Zn

• These ZSB strains produce variety of low molecular weight organic acids, particularly gluconic acid, dissolute the insoluble Zn

• Reduce the pH of the soil solution - increase the plant available zinc (Hafeez et al., 2013). • Zn-fertilizers - 1-5% use efficiency for most of the

crops • ZSB soil bacteria, able to solubilize the inorganic

Zn and thereby increase the bioavailability for crop assimilation.

• Source: Pyrolusite, Hausmannite, Manganite.

• Forms: Mn2+

• Sufficient range of plant: 20 – 500 ppm.

• Fraction: Solution, Exchangeable, Organic, Mineral

Manganese

Mineral Mn

• Mn is found in most Fe-Mg rocks- weathering of primary mineral.• Pyrolusite• Manganite

Soil solution Mn:

• MnSO4 is the most common Mn sources in soil.

• Most common form Mn2+ - 90%.• High pH- Solubility of Mn2+ is low

• Manganese transformation include bacteria, fungi and yeasts. • Bacteria – Leptothrix mobilis - aquatic environment-

oxidizing both iron, manganese. (Nelson et al. 1998)• Oxidize manganous compounds to manganic oxides

(MnO.,) at pH values as low as 6 & some times below 6. (Mulder 1964, Mulder and van Veen 1963).

Transformation of Manganese in soil by

Micro organisms

• Manganese oxidation by a mixture of two bacteria Corynebacterium sp. Chromobacterium sp. has been recorded by Bromfield and Skerman (1950) • Roots of living plants may promote the

solubilization of MnO, by excreting organic acids or other compounds stimulating bacterial activity.

• Source: Malachite, Cupric ferrite, Carbonates, Silicates, Sulfates, Chlorides.• Sufficient range in plants: 5 to 20 ppm.• Forms: Cuprous (Cu+), Cupric (Cu2+)

Copper

• Availability of copper in soil related with the presence of black organic humus.

• H2S forming microorganisms may be involved in copper precipitation.

Transformation of Copper in soil by Micro organisms

Copper precipitation by hydrogen-sulphide-producing

bacteria• Clostridia, Proteus vulgaris, Escherichia coli -

producing H2S from sulphur-containing amino acids (cystine, methionine, glutathion, etc.)- precipitate the Cu • Sulphate-reducing bacteria- precipitate the Cu-

Insoluble form- Assimilatory sulfate reduction

• Sulfate-reducing bacteria are responsible - hydrogen sulfide will react with metal ions to produce metal sulphides. These metal sulphides- insoluble

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