Transcript Primary mineral

Micronutrient elements
Iron & Zinc
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Fe
in the soil
 Fe is one of the most abundant
elements in the surface of the earth.
- makes up about 5% weight of the
earth’s crust
- is invariably present in all soils.
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 iron
bearing Minerals in soils
Primary mineral:
olivine, augite, hornblende and biotite
Secondary minerals - Fe oxides
Geothite (α-FeOOH), haematite and
ferrihydrate
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Iron in the soil solution
1. Soil solution concentrations are very low.
The concentration of Fe3+ in the soil is
~10-15 to 10-20 M.
• Soluble inorganic forms include Fe3+, Fe(OH)2+,
Fe(OH)2+ and Fe2+
• Iron solubility is largely controlled by the
pH and Eh.
• Fe3+ +3OH-= Fe(OH)3
• At higher pH levels Fe3+ activity in solution decrease
1000 fold for each pH unit rise
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Iron in the soil solution
 In aerobic soils , Fe2+ is oxidised to
Fe3+, and f Fe(OH)3 forms and
precipitates.
 In water-saturated soils (anaerobic),
Fe3+ is converted into Fe2+, which
increase Fe solubility.
Fe(OH)3 +e-+3H+
Fe2+ +3H2O
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Siderophores and phytosiderophores
 Siderophores are a kind of organic
substances (such as nicotinamine ,
mugineic acid and avenic acid etc)
produced by bacteria, fungi and plants),
which can form organic complexes or
chelates with Fe3+, and increase the
movement of iron in soil.
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Characteristics of siderophores
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They are molecules with a high affinity
for Fe3+, and remove the Fe from
minerals and contribute to its
dissolution.
These Fe-chelates are highly soluble
and are stable over a wide pH range.
they are of crucial importance for the
Fe transport in soils and the Fe supply
of plants.
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Plant uptake of Fe

Plants can take up both Fe2+ and Fe3+.
 In general, Fe2+ passes through a
special channel of plant membranes.
 Fe3+ is reduced to Fe2+ before
absorption occurs. Fe3+ uptake is
important for grasses
 Phytosiderophores are taken up by
specific transporters located in PM of
graminaceous or monocot roots, and Fe is
reduced in cells.
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Factors that affect Fe uptake
1. Plants have different abilities to take up Fe
from the soil solution
Not only different species (wheat vs. bean) but even
different genotypes.
2. pH
Fe3+ reduction requires a pH of about 5 at the
apoplastic site of the reductase.
The Fe uptake of general plant is affected by the pH, but
Fe uptake of graminaceous monocots is little affected by pH.
3. Ability of Fe3+ reduction in the root
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The Fe2+ in the cytosol is presumably
oxidized in transport into the xylem.
Long- distance transport in the xylem is Fe3+
complex when an excess of citrate in the
xylem.
In the phloem and in the symplasm Fe is
transported as an nicotianamin.
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Fe concentrations in dry plant tissue are
commonly around 50-100 μg/g (compared to N
which is typically 10,000-50,000 μg/g
Most of Fe is in the vegetative parts, grains
and tubes are often considerably low.
The content of iron in the plant is effected
by the soil iron availability.
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Roles of iron in plant
1. Fe is important in the process of chlorophyll and haem
formation in plants
text book p392
2. Fe is required for electron transport in photosynthesis.
It is an important part of several molecules that are
involved in photosynthesis.
Iron sulphur proteins or ferredoxin and ferritin
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3.
Chelate complex Fe is an important electron
acceptor in redox reactions
Haem is prosthetic groups of several enzymes (catalase,
peroxides, cytochrome oxidase etc.).
4.
Nitrogenase comprises an Fe protein and FeMo
protein;
5.
Ribonucleotide reductase. It is required of
synthesis of DNA and RNA, which is required for
the synthesis of proteins.
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Fe deficiency symptoms
1. Interveinal yellowing and chlorosis of whole leaves and
emerging leaves.
Symptoms appear on youngest upper leaves The leaves are
yellow, with the veins remaining green.
2. Whole leaves become chlorotic and pale and reduction of
leave.
3. Not all species are equally susceptible to Fe deficiency
Calcifuge species is susceptible to Fe chlorosis;
The most important commercial crops affected are
citrus, deciduous fruit trees and vine;
Field beans, soybeans, legumes, and tomato etc.
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Iron deficiency in soybeans
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Iron deficiency in rice
Oat Plants Iron deficiency
Young leaves severe chlorosis;
chlorosis begins as interveinal stripes.
Wheat Plants Iron deficiency
Severe chlorosis of leaves,
most severe on younger growths;
die-back of chlorotic leaves
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越橘
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Fe deficiency of grape leaves (up)
Fe deficiency of pear (left and middle of bottom), and apple tree (right of bottom)
Tip leaves chlorotic; small veins show as fine network in early stages; margins
develop brown patches
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Potato Foliage
Iron deficiency
Young leaver strongly chlorotic;
veins may remain green;
margins and tips brown patches.
Potato Foliage
Iron deficiency
Young leaver strongly chlorotic;
veins may remain green;
margins and tips brown patches.
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TOMATO FOLIAGE
Iron deficiency
Tip leaves, especially basal
areas of leaflets,
intense chlorotic mottling; stem
near tip also yellow.
Cabbage Plant (Savoy)
Iron deficiency
Severe chlorosis of leaves
beginning as a chlorotic
mottling.
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• bronzing
of leaves
or
bronzing
disease
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Iron chlorosis may result from an absolute Fe
deficiency in soil, such as organic soils and
degraded sandy soils. But such cases are rare.
However, iron chlorosis occurs frequently on
the calcareous or saline and sodic soils. The
chlorosis is not caused by absolute Fe
deficiency. The Fe concentration in the
chlorotic leaves can be higher than in the
green leaves. Why?
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Calcareous soils, high pH and high HCO3concentrations in soil solution may depress
or even block F3+ reduction in the root
apoplast.
in Calcareous soils, which induce high
apoplastic leaf pH, Fe3+ reduction in the leaf
apoplast is restricted and hence the uptake
of Fe from the apolast into the cytosol is
impaired.
Spraying chlorotic leaves with dilute acids
results in regreening. So does fusicoccin as
well as IAA
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Treatment
Chlorophyll, mg/g/ fresh weight
Pod yield Mg/ha
Control, no spraying
1.37
1.79
H2SO4
1.83
3.36
Fe-EDDH
1.78
3.15
P<0.05
0.676
0.676
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Common Fe Fertilizers
1. Ferrous sulfate, FeSO4·7H2O, (20% Fe)
a) applied to foliage as a solution
b) injected into the tree trunk
2. Iron oxalate, Fe2(C2O4)3, (30% Fe)
3. Iron citrate, FeC6H5O7·X H2O,(16%18% Fe)
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Common Fe Fertilizers
3. Chelated iron
Chelated iron compounds consist of an
organic molecule that binds iron and makes it
solubile in soil solution and more available to
plants.
FeEDDHA, Fe 6%
FeDTPA, Fe10%
FeEDTA, Fe 9-12%
HEDTA, Fe 5-9%
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Common Fe Fertilizers
b) Chelated compounds must be placed into
the root zone to be most effective. Or should
be a foliar application.
Applications should be made in the
spring to coincide with the beginning of
growth.
In most cases, it is necessary to treat the
soil every year.
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A. Soil application can be helpful when the
pH is low, but not at high pH.
B. Alternative methods of Fe-fertilization
include:
1. Foliar application
2. Seed coating
3. Injecting Fe into the tree trunk
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Other management strategies
1. Lower the pH of the soil (increases
soluble Fe
2. Combine the organic matter content
and FeSO4 together.
3. Choose varieties that are not so
sensitive to iron deficiencies.
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zinc content in soil
The total amount of Zn in the soil is
relatively small. The average Zn content of
the soil is 17 to160μg Zn/g soil.
The level of Zn in soils is very much
related to the parent materials.
Basic igneous rocks > siliceous parent
materials
sometimes, pollution soil have high Zn
levels
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Zinc fraction in soil
primary and secondary soil minerals:
augite ，hornblende, and biotite
salts :
ZnS, Sphalerite (ZnFe)S ，smithsonite (ZnCO3)
willemite (Zn2SiO4)
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Soil solution Zn
1. the Zn concentration is very low and in the
3╳10-5 to 5 ╳10-3mol/l.
2. forms of Zn in soil solution
Zn2+, ZnOH+ or ZnCI+
Most of the Zn in the soil solution is usually
in the chelated form
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Exchange Zn
Clay minerals and organic matter have
exchange site of Zn ions.
Specific adsorption of Zn2+ by carbonate:
Magnesite >dolomite>calcite
Adsorption and occlusion of Zn by
carbonate are major cause of poor Zn
availability and the appearance of Zn
deficiency on calcareous soils.
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Organic Zn
Zn can interact with organic matter in soil
Soluble Zn organic complexes is about 60% of
total Zn in soil solution.
Amino acids, organic acids and fulvic acids
complexes with Zn are soluble; but insoluble
organic complexes are derive from humic
acid
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Factors affecting soil Zn availability

pH:
Soluble Zn+2 is ~100 times lower with a
pH increase of 1 unit
organic matter
Zn complexes can either increase or
decrease the availability of Zn to the plant.
carbonate content
History of arable soil
Excess application P fertilizers or iron Mn etc
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Zn Content in plant
For most plant species Zn concentrations
in leaves below 10-15 μg Zn/g dry matter are
indicate Zn deficiency and concentration in
the range of 20 to 100 μg Zn/g dry matter
indicate sufficiency.
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Uptake and translocation
The uptake may be as facilitated
diffusion through membrane channels or
mediated by specific transporters.
The uptake is strongly inhibited by
the Cu, the Fe, Mn and alkaline earths
cations etc.
And is reduced by low temperature.
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Translocation
Zn is not bound to stable ligand.
It is translocated as zinc citrate
complexes
Zn is phloem-mobile, but its
translocation is varies among different
plants.
In the high Zn level, excess Zn is
deposited to a large extent in the older
leaves
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Function of Zn in plants
1. Activates 300 enzymes
Carbonic anhydrase is particularly important
for C4-species.
Alcohol dehydrogenase is important in root
under anaerobic conditions.
Cu-Zn superoxide dismutase (SOD) is required
for the detoxification of the superoxide radical It is
important to resist the sunscald
Enzymes involved in carbohydrate metabolism.
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Function of Zn in plants
2. Necessary for the plant hormone (for example
IAA)
In Zn deficient plant it is low rates of stem
elongation, low auxin activities and low
trytophan
3. Zinc is very closely related to N metabolism of
plant.
RNA polymerase contains Zn
Zinc deficiency affected the structural
integrity of the cytoplasmic ribosomes.
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Deficiency symptoms
1. Stunted (reduced) growth
Unevenly distributed clusters or rosettes
of small stiff leaves (Small, narrow, thick
leaves) are formed at the ends of the
young shoots. Frequently the shoots die off
and leaves fall prematurely.
Apple tree: rosetting and small leaves.
fewer buds, bark is rough and brittle
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2. Chlorosis in the interveinal areas of the leaf
In the monocots chlorotic bands form on
either side of midrib of the leaf which later
become necrotic. The symptoms appears
on young leaves.
In most case, the deficiency symptoms of
vegetable crops is characterized by short
internodes and chlorotic areas in older
leaves. Sometimes chlorosis also appears in
younger leaves.
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Zinc deficiency in corn
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spring
summer
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Zinc deficiency of rice
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•
• Center: healthy shoot from
zinc deficient apple tree;
• Left and Right: shoots
showing zinc deficiency
symptoms; buds along
shoots fail to develop,
leaves small and narrow
("Little Leaf" condition)
and tend to form rosettes
at tips of shoots.
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Excess Zn supply results in reduction of root
and leaf expansion which is followed by
chlorosis. Red-brown pigment was formed
under conditions of excess Zn in soya beans.
Some plants species are Zn tolerant. They can
accumulated 600 to 7800 μg Zn/g dry
matter .
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•
•
Sugar Beet Plants
Zinc toxicity
• Growth severely
stunted; young leaves
show chlorotic iron
deficiency symptoms
followed by severe
intervenal necrosis
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• Excessive Zn of
cucumber: dark
green of older
leave (left).
• Younger leave
shows slight
green with
interveinal
brown spot like
pinhole
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Conditions that may have Zn deficiencies
A. Soils with a high pH (low Zn solubility)
B. Fine-textured soils (Zn adsorption)
C. Cool, wet conditions
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Conditions that may have Zn deficiencies
D. High levels of Cu, Fe, Mn or P can
cause a Zn deficiency
E. Some crops are more sensitive than
others
1. Corn and beans are sensitive
2. Sensitive crops following sugar beets
may have a Zn deficiency.
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Zinc fertilizer
A. Kinds of Zn fertilizer
1. Manure supplies Zn and organic molecules
for chelation
2. ZnSO4 (35% Zn) is most common fertilizer
3. Chelated zinc
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Zinc fertilizer
Application of Zn fertilizer
1. Zn may be applied to the soil or to the
foliage
2. Banding is usually more efficient than
broadcasting – but don’t band P and
Zn together.
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