The rhizosphere
Chapter 4
Aims of this lecture
Summarize properties of the rhizosphere,especially,
Modified from H,Marschner,Fig,15.1
…that are relevant to
plant mineral nutrition
The rhizosphere(根际 )
Rovira 1960?
? Layer of soil surrounding the
growing root that is affected by
the root (concept)
? Usually a few mm wide,up to
say 1 cm (no sharp boundary)*
? Extent depends on plant
properties; e.g.
- Root hair length & density
- Rhizodeposition (exudates etc)
- Nutrient uptake versus supply
Width not to scale
* ‘Mycorrhizospheres’ (菌根际 )can
extend many cm
c
The rhizosphere,soil factors
Rovira 1960?
? Layer of soil surrounding the
growing root that is affected by
the root
? Usually a few mm,up to say 1
cm (no sharp boundary)
? Extent depends on soil
properties; e.g.
- pH & buffering
- Sorption capacity
- Nutrient supply rate
- Microbial populations
- Decomposition of exudates
Width not to scale
The rhizosphere,some conventions
Outer
rhizosphere
500-5000 μm
外根际
Inner rhizosphere
10-500 μm
内根际
Rhizoplane
0-10 μm
根土界面
Root
The rhizosphere,some conventions
Outer rhizosphere
500-5000 μm
Inner rhizosphere
10-500 μm
Rhizoplane
0-10 μm
Root
But defined ‘phases’ may not be helpful because of
gradients (no sharp boundaries)
Gradients in the rhizosphere
Longitudinal & lateral gradients
important for plant nutrition:
- concentrations & composition
- population density & composition
- especially in waterlogged soils
- especially soil bacteria
- especially mycorrhizal fungi
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
Nutrient concentration
Depends on balance between soil supply
and plant uptake; depending in turn on:
? Concentrations in bulk soil
? mobility in soil solution
? mass flow rate
? water content of soil
? rate of uptake into roots
? interactions with microorganisms
Ion mobilities and rhizosphere depletion
Distance moved by diffusion (mm in 6 days)
Soil volumetric water content
NO3-
K+
H2PO4-
0.3
30
3
0.3
0.1
3
0.3
0.03
Diffusion rate depends on
? Ion,
NO3->K+>H2PO4-
? Water content:
High > low
Rhizosphere depletion of P
is common in many soils
P depletion zones in the rhizosphere of maize
and rape,influence of root hairs
Hendriks et al,1981
Distance from root surface (mm)
Isotopically
exchangeable P
(μg ml -1)
150
100
50
1 32
Mean root
hair length
Canola
Maize
Bulk soil
Accumulation of calcium & magnesium in
rhizosphere of barley
0 5 10 15
Distance from root surface (mm)
15
10
5
Available
Mg (mM)
75
50
25
Mg
Ca
Available
Ca (mM)
Roussef & Chino 1987
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
pH changes
Depend on many factors e.g.
? Form of N nutrition
? Soil pH buffering capacity
? Production of organic & amino acids
? Microbial activity
R?mheld 1986
200 kg N/ha
Effect of N form on the rhizosphere pH of barley
NO3- NH4+
H+ uptake (or
OH- hydroxyl
release) during
NO3-
assimilation
H+ release
during NH4+
assimilation
Soil nitrate concentration & rhizosphere pH of maize
R?mheld 1986NO3-N (kg/ha)
75 125 200 400
R?mheld 1986
Rhizosphere pH of chickpea(鹰觜豆 ) with NH4+
supply in soil and different CaCO3 addition
1.5% CaCO3 3.0 6.0
Increasing soil pH & buffering
R?mheld 1986
Rhizosphere pH of different plant species supplied
with 200 kg nitrate/ha
Sorghum
and
chickpea
Barley Lentil(小扁豆 ) Cowpea(豇豆 )
Not all species increase pH
Gahoonia & Nielsen 1992
Rhizosphere pH and P depletion in soil
1 2 3 4 1 2 3 4
pH
P c
on
ce
nt
ra
tio
n (
?g
P/
g so
il)
mm distance from the root surface
5
6
7
260
280
300
100% NO3-
80% NO3-
20% NH4+
canola
Lower rhizosphere pH
improves P availability
R?mheld 1986
P supply and cluster root formation and
rhizosphere pH of white lupin
No P Foliar P
N supplied as NO3-
Cluster roots
formed at low P;
pH decrease is
due to organic
acid extrusion to
mobilise P; - not
associated with
NO3- assimilation
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
- especially in waterlogged soilsRedox potential:
? decreases in waterlogged soil (low O2)
? increases solubility of Mn & Fe
? can lead to production of phytotoxic organic
products.
? Plants,such as rice,adapted to waterlogging
(e.g rice) have ‘oxidation zone’ (to 5 mm) due
to O2 transport from shoot
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
- especially in waterlogged soils
Root products,composition and
concentrations
Many functions:
?Nutrient mobilisation
?Soil detoxification (e.g,Al)
?Substrates for microorganisms
?Stimulation or repellence of microorganisms
?etc
Release of organic material (rhizodeposition)
Sloughed off (removed by friction):
? Cells and cell debris
Organic material exuded (from living cells):
? High molecular weight:
- mucilage粘胶 (polysaccharide多糖 & polyuronic acids多聚糠醛酸 )
- enzymes
Release of organic material (rhizodeposition)
? Low molecular weight:
? - sugars
? - organic acids
? - amino acids
? - phenolics（酚类化合物）
? - others
? CO2 (weak acid) - of organic origin
? H+ - of organic origin (in exchange for mineral
cations,C+)
Main sites of root exudation
Low molecular weight
mucilage
Organic & amino acids
are important in
mobilizing mineral
nutrients
Not to scale
Amounts and composition are affected by
? Plant species & age
? Soil type & properties
? Nutritional status of the plant
? Temperature
? Light intensity and duration
? Presence of microorganisms
Release of organic material (rhizodeposition)
Sugars
Glucose葡萄糖
Fructose果糖
Maltose麦芽糖
Galactose半乳糖
Ribose核糖
Xylose木糖
Rhamnose鼠李糖
Arabinose阿拉伯糖
Raffinose棉子糖
Oligosaccharides
寡聚糖
Amino acids
Leucine亮氨酸
Isoleucine异亮氨酸
Valine缬氨酸
Aminobutyrate
Glutamine
Alanine丙氨酸
Asparagine
Serine丝氨酸
Glutamate
Aspartate
Glycine甘氨酸
Phenylalanine苯丙氨酸
Threonine苏氨酸
Tyrosine酪氨酸
Lysine赖氨酸
Proline脯氨酸
Methionine蛋氨酸
Cystathione胱氨酸
Organic
acids
Oxalate
Malate
Acetate
Propionate
Butyrate
Valerinate甘油
Citrate
Succinate琥
Fumarate延胡羧酸
Glycolate乙醇酸
others
Cinnamic acid 肉桂酸
Chlorogenic acid绿原酸
Flavones类黄酮
Adenine腺嘌呤
Guanine鸟嘌呤
Scopoletin香豆素
Cyanogenes氰化物
Flavonglycosides类黄酮糖苷
Proteins/
Enzymes
Invertase转化酶
Amylase淀粉酶
Protease蛋 白酶
Peroxidase过氧
化物酶
Major components of plant root exudates
Differences between species,organic acid
exudation of legumes under P deficiency
Ohwaki and Hirata 1992
Species
Soybean
Chickpea
Peanut
Pigeon pea
Total
3
66
47
6
Fumaric
1
7
24
1
Citric
1
36
9
1
Malic
1
13
13
4
Malonic
-
7
-
-
nmol/g root fresh wt/ 12h
延胡羧酸 苹果酸 丙二酸
Effect of plant age on sugar exudation from
maize
Matsumoto et al,1979Plant age (days)
Et
ha
no
l s
olu
ble
su
ga
rs
μg
g
fw
-1
30
20
20
10
40 60
Organic 14C exudation along wheat roots
based on Rovira and Davey 1974
Distance from the root tip (cm)
Ra
dio
ac
tiv
ity
(c
pm
)
0
250
500
750
0 10 15 205
Lateral root emergence
Soil types,exudation of organic acids by chickpea
Veneklaas et al,2003
Or
ga
nic
ac
id
co
nc
en
tra
tio
n i
n
rh
izo
sp
her
e (
?m
ol/
g r
oo
t)
0
75
150
Or
ga
nic
ac
id
co
mp
os
iti
on
in
rh
izo
sp
her
e (
%
of
to
ta
l)
0
50
100
Soil
A B C D E F A B C D E F
Soil
Succinate琥珀酸
Malonate丙二酸
Citrate
H,Marschner (1995); Fig,15.10
Root exudates improve solubility of low-
solubility mineral compounds
Soil mechanical impedance increases root
exudation in barley
Barber and Gunn 1974
Plant dw (mg/plant)
Shoot
Root
Exudation (mg/plant)
Amino acids
Carbohydrates
Total
% of root dw
% of total plant dw
Nutrient solution
alone
57
32
0.1
1.5
1.6
5.0
1.8
Nutrient solution
+ glass beads
52
36
0.2
3.0
3.2
9.0
3.7
Bürkert 2003
Release of enzymes
Tarafdar and Jungk 1987
Acid phosphatase activity and organic P depletion in
the rhizosphere of wheat and clover
1 2 3 4 1 2 3 4
Re
lat
ive
un
its
Acid phosphatase activity Organic P concentration
Wheat
Clover
mm distance from the root surface
The effect of P supply on the growth of Lupinus Albus
L,and mineral nutrients content （ the soil was
calcarous soil with pH 8.6）（ Gardner,1982）
Supply rate of SSP（ mg/kgsoil）
0 334 667
Shoot weight (DM g) 1.93 2.01 2.02
Cluster root（ %） 46 28 16
P content in shoot（ %） 0.17 0.20 0.223
Water soluble Mn in the
rhizosphere（ mg/L） 18.7 16.7 5.3
Water soluble Fe in the
rhizosphere（ mg/L） 1.5 0.9 0
? Secretions are very
important for acquiring
Fe because under
aerobic conditions and at
the usual pH of soils,the
concentration of Fe in
the soil solution (? 10-8
M between pH 5 and 9)
is well below the
minimum concentration
for adequate plant
growth,Two strategies
are employed to increase
the availability of Fe.
? Strategy I (below,left) is used by dicots and non-graminaceous monocots,It
involves the secretion of phenolic chelators,acidification of the rhizosphere,
and increased activity of a membrane-bound FeIII reductase,Iron is taken up as
FeII.
? Strategy II (above,right) is found only in the Gramineae and involves the
secretion of specific FeIII chelators called phytosiderophores,These have very
high affinity for FeIII and can mobilise Fe from insoluble sources.
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
-especially mycorrhizal & other fungi
- concentrations & composition
- population density & composition
- especially in waterlogged soils
- especially soil bacteria
Many soil microorganisms
utilise root exudates,
Microorganisms can be
beneficial (e.g,improving
nutrient availability) or
harmful (e.g,competition for
soil nutrients,or root
disease)
mucilage
Distribution of microorganisms along roots
Bacterial colonisation of maize root surface
Root tip Root hair
zone
Lateral root
zone
log
ce
lls
mm
-2
4.0
4.5
5.0
5
15
20
10
% c
ov
er
ag
e
Sch?nwitz and Ziegler 1989
De
ns
ity
(lo
g 7
g-
1 )
Clover Oats Linum Wheat Maize Barley
0
100
200
300 Rhizosphere
Bulk soil
Bacterial population in the rhizosphere of
different plant species
Rovira and Davey 1974
Effects of P-solubilizing bacteria
Dry weight (mg) of lavender（熏衣草） in alkaline soil
Treatment 0 rock phosphate +0.5% rock phosphate
Sterile soil 97 99
+ bacteria* 133 227
[* Pseudomonas & Agrobacterium]
Azcon et al,(1976)
Effects of P-solubilizing bacteria and
mycorrhizal fungus
Dry weight (mg) of lavender in alkaline soil
Treatment 0 rock phosphate +0.5% rock phosphate
Sterile soil 97 99
+ bacteria细菌 133 227
+ Glomus球菌 148 233
+ Glomus & bact,293 403
Azcon et al,(1976)
The effect of some natural fungi on
plant toot growth（ Domsch,1969）
真菌 wheat pea rape
Emericellopsis
（ 翅孢壳菌） 58 70 64
Phoma exigua
（ 茎点霉菌） 75 64 84
Prichocladium
opacum 92 105 104
Verticillium
laterilium（ 砖红轮枝
孢菌属）
104 121 102
Mycorihza 菌根
? Ectomycorrhizal fungi外生菌根菌
? Sheath of fungus (mantle) surrounds root
and may penetrate between outer cells
? Endomycorrhizae内生菌根菌, Vesicular-
Arbuscular Mycorrhizae (VAM)
? Arbuscules form in cortical cells of root
? Hyphae increase surface area for nutrient
exchange
3a Ectomycorrhizal fungi
? Sheath of fungus (mantle) surrounds root and may penetrate between outer cells
? Host forms short,stunted roots but hyphae extend several metres
? Most associations in temperate trees (Beech（ 毛榉）,oak（ 栎树）,Willow,Pine)
? Fungus mobilises P by excreting phosphatases and organic acids
Lodgepole
pine
seedling,
Pinus
contorta,
and fungal
extensions
3 b Endomycorrhizae,
Vesicular-Arbuscular
Mycorrhizae (VAM)
?Arbuscules form in
cortical cells of root
?Increase surface area
for nutrient exchange
Glomus the most common
fungal genus
Hyphae（ 菌丝） extend
roots by 1-10 m per cm
供磷水平、根系分泌物与丹麦草根 VAM
浸染率的关系（ J.H.Graham等,1981）
施磷量
（ mg/kg）
每克干根重的根分泌物 VAM浸染率
（ %）还原糖（ mg） 氨基酸（ mg）
0 3.89 271 89
28 1.22 60 24
56 1.08 50 10
228 1.19 50 5
Infection and energy
? Mycoriza infection is affected by the soil
pH,temperature and plant nutrient
availability etc.
? Species of plant
? soft acid condition
? 20～ 25℃
? P deficient
? photosynthesis
Function of mycorhiza
? Improve host plant P nutrition
? Increase the plant root uptake area,
? Enhance the acid
phosphatase/phytase activity and
rapid the organic P turn over
? Others
? Increase the uptake of K,Cu,Zn and
iron
? Increase the disease resistance
? Allelopathy
? Intercropping
? Under-crop sowing
? Crop rotation
Interacting rhizospheres
Interacting rhizospheres,wheat and lupin with
separated or intertwining roots
Horst and Waschkies 1987
Root systems
Separated
Intertwining
Wheat
20
38
Lupin
33
28
Wheat
19
42
Lupin
42
41
Dry weight
g/pot
P uptake
mg/pot
Conclusions
? The rhizosphere is the interface between
soil and roots
? Its properties depend on many processes
in plants and soil
? A ‘healthy’ rhizosphere – in physical,
chemical and biological terms – is
fundamentally important in influencing
mineral nutrition of plants
Buckwheat,
R?mheld
Chapter 4
Aims of this lecture
Summarize properties of the rhizosphere,especially,
Modified from H,Marschner,Fig,15.1
…that are relevant to
plant mineral nutrition
The rhizosphere(根际 )
Rovira 1960?
? Layer of soil surrounding the
growing root that is affected by
the root (concept)
? Usually a few mm wide,up to
say 1 cm (no sharp boundary)*
? Extent depends on plant
properties; e.g.
- Root hair length & density
- Rhizodeposition (exudates etc)
- Nutrient uptake versus supply
Width not to scale
* ‘Mycorrhizospheres’ (菌根际 )can
extend many cm
c
The rhizosphere,soil factors
Rovira 1960?
? Layer of soil surrounding the
growing root that is affected by
the root
? Usually a few mm,up to say 1
cm (no sharp boundary)
? Extent depends on soil
properties; e.g.
- pH & buffering
- Sorption capacity
- Nutrient supply rate
- Microbial populations
- Decomposition of exudates
Width not to scale
The rhizosphere,some conventions
Outer
rhizosphere
500-5000 μm
外根际
Inner rhizosphere
10-500 μm
内根际
Rhizoplane
0-10 μm
根土界面
Root
The rhizosphere,some conventions
Outer rhizosphere
500-5000 μm
Inner rhizosphere
10-500 μm
Rhizoplane
0-10 μm
Root
But defined ‘phases’ may not be helpful because of
gradients (no sharp boundaries)
Gradients in the rhizosphere
Longitudinal & lateral gradients
important for plant nutrition:
- concentrations & composition
- population density & composition
- especially in waterlogged soils
- especially soil bacteria
- especially mycorrhizal fungi
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
Nutrient concentration
Depends on balance between soil supply
and plant uptake; depending in turn on:
? Concentrations in bulk soil
? mobility in soil solution
? mass flow rate
? water content of soil
? rate of uptake into roots
? interactions with microorganisms
Ion mobilities and rhizosphere depletion
Distance moved by diffusion (mm in 6 days)
Soil volumetric water content
NO3-
K+
H2PO4-
0.3
30
3
0.3
0.1
3
0.3
0.03
Diffusion rate depends on
? Ion,
NO3->K+>H2PO4-
? Water content:
High > low
Rhizosphere depletion of P
is common in many soils
P depletion zones in the rhizosphere of maize
and rape,influence of root hairs
Hendriks et al,1981
Distance from root surface (mm)
Isotopically
exchangeable P
(μg ml -1)
150
100
50
1 32
Mean root
hair length
Canola
Maize
Bulk soil
Accumulation of calcium & magnesium in
rhizosphere of barley
0 5 10 15
Distance from root surface (mm)
15
10
5
Available
Mg (mM)
75
50
25
Mg
Ca
Available
Ca (mM)
Roussef & Chino 1987
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
pH changes
Depend on many factors e.g.
? Form of N nutrition
? Soil pH buffering capacity
? Production of organic & amino acids
? Microbial activity
R?mheld 1986
200 kg N/ha
Effect of N form on the rhizosphere pH of barley
NO3- NH4+
H+ uptake (or
OH- hydroxyl
release) during
NO3-
assimilation
H+ release
during NH4+
assimilation
Soil nitrate concentration & rhizosphere pH of maize
R?mheld 1986NO3-N (kg/ha)
75 125 200 400
R?mheld 1986
Rhizosphere pH of chickpea(鹰觜豆 ) with NH4+
supply in soil and different CaCO3 addition
1.5% CaCO3 3.0 6.0
Increasing soil pH & buffering
R?mheld 1986
Rhizosphere pH of different plant species supplied
with 200 kg nitrate/ha
Sorghum
and
chickpea
Barley Lentil(小扁豆 ) Cowpea(豇豆 )
Not all species increase pH
Gahoonia & Nielsen 1992
Rhizosphere pH and P depletion in soil
1 2 3 4 1 2 3 4
pH
P c
on
ce
nt
ra
tio
n (
?g
P/
g so
il)
mm distance from the root surface
5
6
7
260
280
300
100% NO3-
80% NO3-
20% NH4+
canola
Lower rhizosphere pH
improves P availability
R?mheld 1986
P supply and cluster root formation and
rhizosphere pH of white lupin
No P Foliar P
N supplied as NO3-
Cluster roots
formed at low P;
pH decrease is
due to organic
acid extrusion to
mobilise P; - not
associated with
NO3- assimilation
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
- especially in waterlogged soilsRedox potential:
? decreases in waterlogged soil (low O2)
? increases solubility of Mn & Fe
? can lead to production of phytotoxic organic
products.
? Plants,such as rice,adapted to waterlogging
(e.g rice) have ‘oxidation zone’ (to 5 mm) due
to O2 transport from shoot
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
Mycorrhizal &
other fungi
- concentrations & composition
- population density & composition
- especially in waterlogged soils
Root products,composition and
concentrations
Many functions:
?Nutrient mobilisation
?Soil detoxification (e.g,Al)
?Substrates for microorganisms
?Stimulation or repellence of microorganisms
?etc
Release of organic material (rhizodeposition)
Sloughed off (removed by friction):
? Cells and cell debris
Organic material exuded (from living cells):
? High molecular weight:
- mucilage粘胶 (polysaccharide多糖 & polyuronic acids多聚糠醛酸 )
- enzymes
Release of organic material (rhizodeposition)
? Low molecular weight:
? - sugars
? - organic acids
? - amino acids
? - phenolics（酚类化合物）
? - others
? CO2 (weak acid) - of organic origin
? H+ - of organic origin (in exchange for mineral
cations,C+)
Main sites of root exudation
Low molecular weight
mucilage
Organic & amino acids
are important in
mobilizing mineral
nutrients
Not to scale
Amounts and composition are affected by
? Plant species & age
? Soil type & properties
? Nutritional status of the plant
? Temperature
? Light intensity and duration
? Presence of microorganisms
Release of organic material (rhizodeposition)
Sugars
Glucose葡萄糖
Fructose果糖
Maltose麦芽糖
Galactose半乳糖
Ribose核糖
Xylose木糖
Rhamnose鼠李糖
Arabinose阿拉伯糖
Raffinose棉子糖
Oligosaccharides
寡聚糖
Amino acids
Leucine亮氨酸
Isoleucine异亮氨酸
Valine缬氨酸
Aminobutyrate
Glutamine
Alanine丙氨酸
Asparagine
Serine丝氨酸
Glutamate
Aspartate
Glycine甘氨酸
Phenylalanine苯丙氨酸
Threonine苏氨酸
Tyrosine酪氨酸
Lysine赖氨酸
Proline脯氨酸
Methionine蛋氨酸
Cystathione胱氨酸
Organic
acids
Oxalate
Malate
Acetate
Propionate
Butyrate
Valerinate甘油
Citrate
Succinate琥
Fumarate延胡羧酸
Glycolate乙醇酸
others
Cinnamic acid 肉桂酸
Chlorogenic acid绿原酸
Flavones类黄酮
Adenine腺嘌呤
Guanine鸟嘌呤
Scopoletin香豆素
Cyanogenes氰化物
Flavonglycosides类黄酮糖苷
Proteins/
Enzymes
Invertase转化酶
Amylase淀粉酶
Protease蛋 白酶
Peroxidase过氧
化物酶
Major components of plant root exudates
Differences between species,organic acid
exudation of legumes under P deficiency
Ohwaki and Hirata 1992
Species
Soybean
Chickpea
Peanut
Pigeon pea
Total
3
66
47
6
Fumaric
1
7
24
1
Citric
1
36
9
1
Malic
1
13
13
4
Malonic
-
7
-
-
nmol/g root fresh wt/ 12h
延胡羧酸 苹果酸 丙二酸
Effect of plant age on sugar exudation from
maize
Matsumoto et al,1979Plant age (days)
Et
ha
no
l s
olu
ble
su
ga
rs
μg
g
fw
-1
30
20
20
10
40 60
Organic 14C exudation along wheat roots
based on Rovira and Davey 1974
Distance from the root tip (cm)
Ra
dio
ac
tiv
ity
(c
pm
)
0
250
500
750
0 10 15 205
Lateral root emergence
Soil types,exudation of organic acids by chickpea
Veneklaas et al,2003
Or
ga
nic
ac
id
co
nc
en
tra
tio
n i
n
rh
izo
sp
her
e (
?m
ol/
g r
oo
t)
0
75
150
Or
ga
nic
ac
id
co
mp
os
iti
on
in
rh
izo
sp
her
e (
%
of
to
ta
l)
0
50
100
Soil
A B C D E F A B C D E F
Soil
Succinate琥珀酸
Malonate丙二酸
Citrate
H,Marschner (1995); Fig,15.10
Root exudates improve solubility of low-
solubility mineral compounds
Soil mechanical impedance increases root
exudation in barley
Barber and Gunn 1974
Plant dw (mg/plant)
Shoot
Root
Exudation (mg/plant)
Amino acids
Carbohydrates
Total
% of root dw
% of total plant dw
Nutrient solution
alone
57
32
0.1
1.5
1.6
5.0
1.8
Nutrient solution
+ glass beads
52
36
0.2
3.0
3.2
9.0
3.7
Bürkert 2003
Release of enzymes
Tarafdar and Jungk 1987
Acid phosphatase activity and organic P depletion in
the rhizosphere of wheat and clover
1 2 3 4 1 2 3 4
Re
lat
ive
un
its
Acid phosphatase activity Organic P concentration
Wheat
Clover
mm distance from the root surface
The effect of P supply on the growth of Lupinus Albus
L,and mineral nutrients content （ the soil was
calcarous soil with pH 8.6）（ Gardner,1982）
Supply rate of SSP（ mg/kgsoil）
0 334 667
Shoot weight (DM g) 1.93 2.01 2.02
Cluster root（ %） 46 28 16
P content in shoot（ %） 0.17 0.20 0.223
Water soluble Mn in the
rhizosphere（ mg/L） 18.7 16.7 5.3
Water soluble Fe in the
rhizosphere（ mg/L） 1.5 0.9 0
? Secretions are very
important for acquiring
Fe because under
aerobic conditions and at
the usual pH of soils,the
concentration of Fe in
the soil solution (? 10-8
M between pH 5 and 9)
is well below the
minimum concentration
for adequate plant
growth,Two strategies
are employed to increase
the availability of Fe.
? Strategy I (below,left) is used by dicots and non-graminaceous monocots,It
involves the secretion of phenolic chelators,acidification of the rhizosphere,
and increased activity of a membrane-bound FeIII reductase,Iron is taken up as
FeII.
? Strategy II (above,right) is found only in the Gramineae and involves the
secretion of specific FeIII chelators called phytosiderophores,These have very
high affinity for FeIII and can mobilise Fe from insoluble sources.
Gradients in the rhizosphere
Longitudinal & lateral
gradients:
-especially mycorrhizal & other fungi
- concentrations & composition
- population density & composition
- especially in waterlogged soils
- especially soil bacteria
Many soil microorganisms
utilise root exudates,
Microorganisms can be
beneficial (e.g,improving
nutrient availability) or
harmful (e.g,competition for
soil nutrients,or root
disease)
mucilage
Distribution of microorganisms along roots
Bacterial colonisation of maize root surface
Root tip Root hair
zone
Lateral root
zone
log
ce
lls
mm
-2
4.0
4.5
5.0
5
15
20
10
% c
ov
er
ag
e
Sch?nwitz and Ziegler 1989
De
ns
ity
(lo
g 7
g-
1 )
Clover Oats Linum Wheat Maize Barley
0
100
200
300 Rhizosphere
Bulk soil
Bacterial population in the rhizosphere of
different plant species
Rovira and Davey 1974
Effects of P-solubilizing bacteria
Dry weight (mg) of lavender（熏衣草） in alkaline soil
Treatment 0 rock phosphate +0.5% rock phosphate
Sterile soil 97 99
+ bacteria* 133 227
[* Pseudomonas & Agrobacterium]
Azcon et al,(1976)
Effects of P-solubilizing bacteria and
mycorrhizal fungus
Dry weight (mg) of lavender in alkaline soil
Treatment 0 rock phosphate +0.5% rock phosphate
Sterile soil 97 99
+ bacteria细菌 133 227
+ Glomus球菌 148 233
+ Glomus & bact,293 403
Azcon et al,(1976)
The effect of some natural fungi on
plant toot growth（ Domsch,1969）
真菌 wheat pea rape
Emericellopsis
（ 翅孢壳菌） 58 70 64
Phoma exigua
（ 茎点霉菌） 75 64 84
Prichocladium
opacum 92 105 104
Verticillium
laterilium（ 砖红轮枝
孢菌属）
104 121 102
Mycorihza 菌根
? Ectomycorrhizal fungi外生菌根菌
? Sheath of fungus (mantle) surrounds root
and may penetrate between outer cells
? Endomycorrhizae内生菌根菌, Vesicular-
Arbuscular Mycorrhizae (VAM)
? Arbuscules form in cortical cells of root
? Hyphae increase surface area for nutrient
exchange
3a Ectomycorrhizal fungi
? Sheath of fungus (mantle) surrounds root and may penetrate between outer cells
? Host forms short,stunted roots but hyphae extend several metres
? Most associations in temperate trees (Beech（ 毛榉）,oak（ 栎树）,Willow,Pine)
? Fungus mobilises P by excreting phosphatases and organic acids
Lodgepole
pine
seedling,
Pinus
contorta,
and fungal
extensions
3 b Endomycorrhizae,
Vesicular-Arbuscular
Mycorrhizae (VAM)
?Arbuscules form in
cortical cells of root
?Increase surface area
for nutrient exchange
Glomus the most common
fungal genus
Hyphae（ 菌丝） extend
roots by 1-10 m per cm
供磷水平、根系分泌物与丹麦草根 VAM
浸染率的关系（ J.H.Graham等,1981）
施磷量
（ mg/kg）
每克干根重的根分泌物 VAM浸染率
（ %）还原糖（ mg） 氨基酸（ mg）
0 3.89 271 89
28 1.22 60 24
56 1.08 50 10
228 1.19 50 5
Infection and energy
? Mycoriza infection is affected by the soil
pH,temperature and plant nutrient
availability etc.
? Species of plant
? soft acid condition
? 20～ 25℃
? P deficient
? photosynthesis
Function of mycorhiza
? Improve host plant P nutrition
? Increase the plant root uptake area,
? Enhance the acid
phosphatase/phytase activity and
rapid the organic P turn over
? Others
? Increase the uptake of K,Cu,Zn and
iron
? Increase the disease resistance
? Allelopathy
? Intercropping
? Under-crop sowing
? Crop rotation
Interacting rhizospheres
Interacting rhizospheres,wheat and lupin with
separated or intertwining roots
Horst and Waschkies 1987
Root systems
Separated
Intertwining
Wheat
20
38
Lupin
33
28
Wheat
19
42
Lupin
42
41
Dry weight
g/pot
P uptake
mg/pot
Conclusions
? The rhizosphere is the interface between
soil and roots
? Its properties depend on many processes
in plants and soil
? A ‘healthy’ rhizosphere – in physical,
chemical and biological terms – is
fundamentally important in influencing
mineral nutrition of plants
Buckwheat,
R?mheld
