Semester -5th

Paper – Environmental MicrobiologyTopic- Phosphorus cycle

BY: KHAN SHAH RUKHRoll no : 4181457022

Submitted to: Dr. Anjana KapoorCollege / Department: MICROBIOLOGY, SSN College ;University of Delhi

CONTENT

Schematic representation of the importance of microorganisms to P availability in soil.

©2011 by American Society of Plant Biologists

Inorganic P Compounds(precipitates)

Acid soils Fe and Al phosphates

FePO4l2H2O , AlPO4

l2H2O

Alkaline soils

Ca and Mg phosphates

Ca(H2PO4)2 monocalcium phosphate

CaHPO4 dicalcium phosphate

Ca3(PO4)2 tricalcium phosphate

3Ca3(PO4)2lCa(OH)2 hydroxyapatite

3Ca3(PO4)2lCaCO3 carbonate apatite

Organic Soil Phosphorus

* 20 - 50% of total soil P is organic• Mostly inositol phosphates, • Humic acid• Phospholipids• Phosphate sugars• Nucleic acids

•

• Immobilization (or demineralisation) in soil science is the conversion of inorganic compounds to organic compounds by micro-organisms , by which it is prevented from being accessible to plants . Immobilization is the opposite of mineralization.

Factors affecting immobilization:-

Soil organic and inorganic matterpH of soilPresence of microbs in soil

MINERALIZATION OF ORGANIC P

• Mineralization is the microbial conversion of organic P to H2PO4-or HPO4

2-, forms of plant available P known as orthophosphate.• Mixed cultures of PSMs (Bacillus, treptomyces,

Pseudomonas etc.) are most effective in mineralizing organic phosphate (Molla et al., 1984).

• Enterobacter agglomerans solubilizes hydroxyapatite and hydrolyze the organic P (Kim et al .,1998).

P-mineralizing microorganisms

P-solubilizing microorganisms• Bacteria e.g. Actinomycetes, Pseudomonas, and Bacillus spp.• Fungi e.g. Aspergillus and Penicillium spp.• A nematofungus Arthrobotrys oligospora also has the

ability to solubilize the phosphate rocks (Duponnois et al., 2006).

• Phosphorus solubilizing activity is determined by the ability of microbes to release metabolites such as organic acids, which through their hydroxyl and carboxyl groups chelate the cation bound to phosphate, the latter being converted to soluble forms

Mechanisms of phosphate solubilization

• Chelating-mediated mechanism

Hydroxyl and carboxyl groups of acids chelate cations (Al, Fe, Ca)

Decrease the pH in basic soils

â Ca(H2PO4)2 â monocalcium phosphate

â CaHPO4â dicalcium phosphate

â Ca3(PO4)2â tricalcium phosphate

â 3Ca3(PO4)2lCa(OH)2â hydroxyapatite

â 3Ca3(PO4)2lCaCO3â carbonate apatite

decreasing solubilityInorganic P Compounds

pH

6

8

• Inorganic acids e.g. hydrochloric acid can also solubilize phosphate but they are less effective compared to organic acids at the same pH (Kim et al., 1997).

• In certain cases phosphate solubilization is induced by phosphate starvation (Gyaneshwar et al., 1999).

PHOSPHORUS CYCLE

MICROBIAL SINK

Mineralization

Immobiliz

ation

Weathering

Eutrophication WATERBODIES and SEDIMENTS

Land Application

Aide

d by

Myc

orrh

iza

Microbial D

ecompositi

on

MINERALFERTILIZER

HUMAN and ANIMAL EXCREMENT(~50% of P in phytic acid form)

ROCKBOUND•Apatite•Fluorapatite•Chlorapatite•Hydroxlapatite

PLANT UPTAKE as H2PO4-

or HPO42-

SOILINORGANIC PORGANIC P

•Humic acid•Inositol phosphates•Phospholipids•Phosphate sugars•Nucleic acids

Non-Labile Labile Soil Solution•Specific adsorption to Fe, Al,+ Mn oxides and broken clay edges• Precipitation of Ca or Mg-P at pH>7•Precipitation of Fe, Al, or Mn-P at pH<5

•Weakly sorbed phosphates•Newly-precipitated Fe, Al, or Mn-P in acid soils•Newly precipitated Ca or Mg-P in alkaline soils

•Phosphate released from labile pool or added via fertilizer

LEACHING

SURFACE RUNOFF

WIND EROSION

PLANT and ANIMAL RESIDUES

Eutro

phica

tion

HUMAN and ANIMAL CONSUMPTION

By: Damon Wright, 2000; Clyde Alsup and Michelle Armstrong, 1998; Asrat Shaiferaw, 1994; and Jerry Speir, 1996

Summary

Additional Information on Phosphorus

• Form taken up by plant: H2PO4-, HPO4

= • Mobility in soil: None; roots must come in direct

contact with orthophosphate P • Mobility in plant: Yes • Deficiency symptoms: Lower leaves with purple leaf margins• Deficiency pH range: <5.5 and >7.0 • Toxicity symptoms: None

Toxicity pH range: Non toxic (optimum availability pH 6.0-6.5) • Role in plant growth: Important component of phospholipids

and nucleic acids (DNA and RNA) • Role in microbial growth: Accumulation and release of energy

during cellular metabolism • Concentration in plants: 1,000 – 5,000 ppm (0.1 –0.5%) • Effect of pH on availability: H2PO4

- at pH < 7.2• HPO4

= at pH > 7.2 • Interactions with other P x N, P x Zn at high pH, in anion

nutrients: exchange P displaces S, K by mass action displaces Al inducing P deficiency (pH<6.0)

MORE INFO

• P fertilizer sources: Rock phosphate, phosphoric acid, Ca orthophosphates, ammoniumphosphates,

ammonium poly-phosphates, nitric phosphates, K phosphates, microbial fertilizers (phosphobacterins) increase P uptake

• Additional categories: • Mineralization/ C:P ratio of < 200: net mineralization of

immobilization: organic P; C:P ratio of 200-300: no gain/loss of inorganic P; C:P ratio of >300: net immobilization of

inorganic P • P fixation: Formation of insoluble Ca, Al, and Fe phosphates• Al(OH)3 + H2PO4

- Al(OH)2HPO4

• (Soluble) (Insoluble)• Organic P sources: Inositol phosphate (Esters of orthophosphoric acid),

phospholipids, nucleic acids, phosphate sugars

• Inorganic P sources: Apatite and Ca phosphate (unweathered soils) and Fe and Al sinks from P fixation (weathered soils)

• Waste: Poultry litter (3.0 to 5.0%), steel slag (3.5%), electric coal ash (<1.0%)

Additional Information on Phosphorus (Cont.)

MORE INFO

• Total P levels in soil: 50 – 1500 mg/kg• Solution concentration range: < 0.01 to 1.0 ppm• Applied fertilizer: < 30% recovered in plants, more P

must be added than removed by crops

Additional Information on Phosphorus (Cont.)

References:• Alexander, M., 1977. Introduction to Soil Microbiology. 2nd Edition. John Wiley and Sons, NY.• Brady, N.C., 1990. The Nature and Properties of Soils. 10th Edition. Macmillan Publishing Co.,

NY.• Brigham Young University. 1997. The Phosphorus Cycle.

http://ucs.byu.edu/bioag/aghort/214pres/geochem.htm• Harrison, A.F., 1987. Soil Organic Phosphorus. A Review of World Literature. C.A.B. p.39.• Pierre, W.H., 1948. The Phosphorus Cycle and Soil Fertility. J. Amer. Soc. of Agron., 40:1-14.• Pierzynski, G.M., Sims, J.T., and Vance, G.F., 1994. Soil and Environmental Quality. Lewis

Publishers, FL.• Stewart, J.W.B., and Sharpley, A.N., 1987. Controls on Dynamics of Soil and Fertilizer

Phosphorus and Sulfur in Soil Fertility and Organic Matter as Critical Components of Production Systems, SSSA Spec. Pub. No.19, 101-121.

• Tiessen, H., 1995. Phosphorus in the Global Environment – Transfers, Cycles and Management. John Wiley and Sons, NY.

• Tisdale, S.L., Nelson, W.L., Beaton, J.D. and Havlin, J.L., 1993. Soil Fertility and Fertilizers. Macmillan Publishing Co., NY.

MICROBIAL ECOLOGY:• Fundamentals and applications by Atlas RM and Bartha 4th ED. SOIL MICROBIOLOGY:• An Exploratory Approach MICROBIOLOGY• Prescott, Harley and Klein`s 7th ED. www.google.com• For images