Chapter 1
Essential elements
? Plant nutrition is a term that
takes into account the
interrelationships of mineral
elements in the growth medium
as well as their role in plant
growth,
Concept of plant nutrition
Concept of plant nutrition
? Complex interactions involving
weathering（风化） of rock minerals,
decaying(腐解） of organic matter,
such as humus and residues of
plant,animals,and microbes,take
place to form inorganic minerals in
soil,
? Roots absorb mineral nutrients as
ions in soil water,Many factors
influence nutrient uptake for
plants,
? This interrelationship involves a
complex balance of mineral
elements essential and beneficial
for optimum plant growth.
Concept of plant nutrition
Essential elements
? The material of living plants consist
of organic matter,water and
minerals,The percentage distribution
of these three components is in the
following order of magnitude:
? Water 70%(fresh matter)
? Organic material 27%(fresh matter)
? Minerals 3% (fresh matter)
? The term essential mineral
element (or mineral nutrient) was
proposed by Arnon and Stout
(1939),
? They concluded three criteria(标
准 ) must be met for an element
to be considered essential(必需的 ).
Essential elements
Three criteria of Essential elements
? 1,A plant must be unable to
complete its life cycle in the absence
of the mineral element,
? 2,The function of the element must
not be replaceable by another
mineral element,or deficiency
symptoms can not be remedied by
supplying some other element
? 3,The element must be directly
involved in plant metabolism.
Sixteen Essential Elements
Carbon (C) Hydrogen (H) Oxygen (O)
Nitrogen (N) Phosphorus (P) Potassium (K)
Calcium (Ca) Magnesium (Mg) Sulfur (S)
Iron (Fe) Manganese (Mn) Copper (Cu)
Zinc (Zn) Molybdenum (Mo) Boron (B)
Chlorine (Cl)
Nutrient Composition of Plants
Relative amounts of essential elements in plant tissues
Two ways to classify the essential elements
1,Classified by whether it is used in large or
small amounts
(Macronutrients or micronutrients)
2,Classified by its function in the plant
(What the element does in the plant)
Macronutrients and Micronutrients
A,Macronutrients are elements that are used in
relatively large amounts (% or g/kg).
B,Micronutrients are elements that are used in
relatively small amounts (μ g/g or mg/kg).
The concentration of macronutrients in plant
tissue is often more than 1000x greater than
the concentration of micronutrients.
Carbon (C) Hydrogen (H) Oxygen (O)
Nitrogen (N) Phosphorus (P) Potassium (K)
Calcium (Ca) Magnesium (Mg) Sulfur (S)
? N,P,and K are called primary macronutrients
? Ca,Mg,and S are called secondary
macronutrients
Macronutrients
Micronutrients
Iron (Fe) Manganese (Mn) Copper (Cu)
Zinc (Zn) Molybdenum (Mo) Boron (B)
Chlorine (Cl)
表 1-1 正常生长的植株中营养元素的平均含量（ Stout,P.R.）
元素 干物质中的含量 相当于钼原
子数的倍数μmol/g μg/g %
Mo 0.001 0.1 1
Cu 0.10 6.0 100
Zn 0.30 20 300
Mn 1.0 50 1000
B 2.0 20 2000
Fe 2.0 100 2000
CI 3.0 100 3000
S 30 0.1 30000
P 60 0.2 60000
Mg 80 0.2 80000
Ca 125 0.5 125000
K 250 1.0 250000
N 1000 1.5 1000000
O 30000 45 30000000
C 40000 45 40000000
H 60000 6 60000000
Concentrations of essential elements in leaves
s uga r c a ne r i c e c or n S oyb e a n
ma c r onu t r i e nt s %
N i t r oge n 1,5 2,5 3,0 4,0
P ot a s s i um 2,2 1,0 1,9 1,7
P hos pho r u s 0,05 0,1 0,25 0,26
M a gne s i um 0,1 0,1 0,25 0,25
S ul f ur 0,1 0,1 0,2 0,25
C a l c i um 0,1 0,15 0,15 0,15
m i c r onu t r i e nt s p pm
I r on 10 70 15 50
C hl or i ne 20 25
M a nga ne s e 20 20 15 20
Z i nc 10 10 15 20
B or on 1 3 10 20
C opp e r 2 5 5 10
S i l i c on 5
M ol ybd e num < 0,1 < 0,1 0,1 0,7
Data,represent the lowest concentrations found in recently matured leaves of healthy plants.
Higher levels are commonly found
? Among the all of nutrients,N,P and K are
three most important ones in crops
production because the amount of plant
required is bigger but their availability are
lower in the soil,so they are often
deficiency to crop in the field,and they are
needed to compensated by fertilizers,
Three primary fertilizers (肥料三要素）
or primary macronutrients
表 1-2几种作物每吨生物量所需的 N,P2O5和 K2O（ kg）
Requirement of N,P2O5 and K2O of some kinds of crops (kg/tone biomass)
作物 N P2O5 K2O
黑麦 40 15 44
春小麦 47 15 41
冬小麦 51 15 39
大麦 36 14 38
多年生牧草 29 13 38
晚马铃薯 9 3 11
菜豆 6 2 8
大白菜 6 3 12
黄瓜 5 2 8
番茄 5 2 5
芜箐
Crop
Base
Yield
tonnes/h
a Estimated Nutrient Removal kg/ha
Corn 9.1 135 68 47
Wheat 5 118 49 30
Wheat+straw 5 165 59 138
Soybeans 3 217 47 78
Canola 2.5 106 62 30
Cotton
(seed+lint) 1.7 45 11 14
Sugar beets 50 20 250 40
Nutrient Removal by Crops
N P2O5 K2O
Factors that affect the mineral content in the plant
1,Genotypes,Ability of the plant to take up
nutrients
2,Availability of the nutrient in the soil or water
etc.
3,Portion of the plant (leaf compared to fruit)
4,Age of the plant
The special functions of the element must not be
replaceable by another mineral element
营养元素的同等重要律与不可代替律
? No matter how much is required by
the plant,or how much content is it
in plant,the every essential element
is same important to the plant
physiology and plant growth; its
function of every essential element
cannot substitute by another mineral
element completely.
? Beneficial elements are those that can
compensate for toxic effects of other
elements or may replace mineral nutrients
in some other less specific function such
as the maintenance of osmotic pressure.
? The beneficial elements have not been
deemed essential for all plants but may be
essential for some,
Beneficial elements
? Cobalt for instance is essential for
nitrogen fixation in legumes,
? Silicon,Equisetum（木贼属） and many
grasses (particularly rice) require silicon,
deposited in cell walls,has been found
to improve heat and drought(干旱 )
tolerance and increase resistance to
insects and fungal infections,
Beneficial elements
Silicon,acting as a beneficial
element,can help compensate for toxic
levels of manganese,iron,sodium and
aluminum as well as zinc deficiency.
Na is required by species using the
C4 pathway of photosynthesis,Where it
is supposed to maintain the integrity of
chloroplasts and thus allow the uptake
of pyruvate（丙酮酸）
Beneficial elements
? Plant nutrients and toxins are important
components of food chains that begin with
plants and include animals-wild,domestic,
and human
? Deficiencies of the essential elements
frequently limit plant growth or quality,Even
when the plants themselves do not suffer from
a deficiency,they sometimes provide animals
with a diet deficient in certain elements,for
example,Mo,Se,Co,Cu,P,Na,Ca,or I
Essential elements and food chain
Essential elements and food chain
? A more holistic approach(整体分析）
to plant nutrition would not be
limited to nutrients essential to
survival but would include mineral
elements at levels beneficial for
optimum growth and food chain,
More toxic element
? Plants frequently contain unnecessary
high and sometimes toxic
concentrations of an essential or
nonessential element,Most commonly
toxic to plant are AI and Mn (in acid
soils),Na,and CI (in saline soils),
boron,and copper,
? Elements such as copper,lead,arsenic,
cadmiun,molybdenum,and selenium
are sometimes present at
concentrations that injure foraging
animals,though the plant itself is little
affected,
Phytoremediation (植物修复）
? Plant are very adaptive(适应性 )
? The plants,which can uptake and
accumulation high level metal,is known
as hyperaccumulators,
? Now 45 plant families are known to
contain metal-accumulating species.
? The decontamination（净化） of soil by
means of plants uptake of organic and /or
inorganic contaminants is called
phytoremediation,
Specific function
Structural components结构物质 (C,H,O,N,P,S)
Enzymes activators 酶活化剂 (K,Ca,Mg,Mn,Zn)
Redox reaction 氧化反应 (Fe,Cu,Mn,Mo)
Elements of uncertain function未知功能 (B,CI)
The function of essential nutrients
NON-SPECIFIC OSMOTIC FUNCTIONS
The generation of turgor（膨压） in walled cells depends on
the accumulation of inorganic and organic solutes within the
vacuoles（液泡） and cytoplasm（原生质） of plant
K+ is energetically much cheaper than organic solutes,Indeed
K+ is typically the preferred cation（阳离子） for turgor
generation in land plants.
For halophytes（盐生植物）,NaCl is an important
osmoticum（渗透物质） but it is restricted to the vacuole
The function of essential nutrients
C,H,O,N,and S are the major components of the
plant tissue,Essential elements of atomic groups
which are involved in enzymic processes
P,B,and Si are important in esterfication (酯化作
用 )processes,P esters are involved in the energy
transfer reactions
Classified by function
Classified by function
K,Na,Mg,Ca,Mn,and Cl control the
movement of water and ions between
cells,Non-special functions (osmotic
potentials) and special function
(enzyme activation)
Fe,Cu,Zn,and Mo enable electron
transport by valency change.
2,Flow of the nutrients from
soil to the root
N u trie n t u p t a ke s te p s
nu t
M ove m en t t h r o ug h so il
C ell w all C ell m embran e
C ell to cell tran sp ortvascu l a r tissue
un loa d i n g
nutrient
How do plant roots and nutrients come into contact?
Root interception
离子代换或截获
Mass flow
质流
Diffusion
扩散
Root Interception(截获）
Roots grow through soil
and come into contact
with the surfaces of soil
particles,The root
surfaces are able to take
up the nutrients from soil
clay mineral,
离子代换
Root Interception
Roots only occupy about 1-2% of the
total soil volume,so the amount of
nutrients take up in this way is relatively
small,
But It is most significant for,
1.High concentrations in soil solution such as
Ca and Mg(?)
2.Nutrients required in small amounts (e.g,Zn,
Mn,and other micronutrients)
Mass Flow (or bulk flow)质流
Nutrients are transported as water
moves from the soils to the plant
roots.
or soil solution
(containing dissolved
nutrients) moves down
gradients of water potential
水吸力 毛管力
根压
? The characteristics of mass flow
? Wet soil ? dry soil
? Higher water potential ?lower water potential
? All nutrients move in the same direction
? Rate of nutrient movement depends on
– concentration in solution - affected by uptake and
replacement
– volume of solution - affected by soil moisture and
by soil pore sizes
– rate of flow - affected by transpiration(蒸腾）,
evaporation（蒸发） and drainage（排水）
Mass Flow (or bulk flow)质流
Mass flow supplies most of the required
amounts of NO3-,SO42-,Cl-,and H3BO3
It often supplies more than the required
amounts of Ca,Mg.
It can meet or supply a significant portion of
the requirements for Cu,Mn,and Mo.
Mass Flow (or bulk flow)质流
Factors that affect nutrient transport by mass flow
1,Soil water content – if the soil is dry water
move very slowly.
2,Temperature– if the temperature is low,
water uptake by the plant is reduced and
nutrient transport declines,
3,Air humid
Diffusion(扩散）
Diffusion occurs
when an ion is
transported from a
place of higher
concentration to a
place of lower
concentration.
Diffusion
As plants take up nutrients,there is a
reduction in the nutrient concentration near
to the root (rhizosphere),So the nutrient
concentration in bulk soil solution is higher
then that in rhizosphere,then nutrients will
begin to move into the area near to the root
surface,
Nutrient concentration is different at the root surface compared
to the soil solution,If the difference in the concentration is
very large,then diffusion can occur more rapidly,Diffusion is
an important mechanism for the movement of NH4+,P,K,Fe,
and Zn,
图２根系附近土壤养分耗竭模式
Canola 油菜Corn 玉米
Diffusion of nutrients
? Movement in solution is independent of direction
of flow of solution
? Nutrient moves down concentration gradient
? Rate for each nutrient depends on
– concentration gradient (driving force)
– diffusion coefficient in soil (D) (ease of movement)
– D=Di Φf ╳ Dcs/Dc
– Diffusion coefficient in water (Di)
– buffering capacity of soil (Dcs/Dc)
– tortuosity of pathway in soil (f)
– soil moisture (continuity of water-filled pores)(Φ)
Di = diffusion coefficient of ions in soil (m2 s-1)
ion wet soil
-10 kPa
dry soil
-1000 kPa
NO3-
(low buffering capacity)
10-9 10-11
K+ 10-11 10-13
H2PO4-
(high buffering capacity)
10-13 10-15
values are much lower than for diffusion in pure water(0.5-2.0 ╳ 10-9)due
to,
? tortuosity(曲折度 ) of pathway
? increased viscosity(粘滞性） close to surfaces
? exclusion（排斥） of ions by surface charge on particles
Processes involved in nutrient replacement
replacement at root surface N P
diffusion rapid slow
mass flow +++ (+)
N has low buffering capacity and high
concentration in soil solution
N is VERY MOBILE (easily gets to roots; easily
leached out of soil)
P has high buffering capacity and low
concentration in soil solution (<10μM)
P is VERY IMMOBILE
1
23soil
根
shoot
1,Root interception; 2,diffusion; 3,mass flow
root
Essential elements
? Plant nutrition is a term that
takes into account the
interrelationships of mineral
elements in the growth medium
as well as their role in plant
growth,
Concept of plant nutrition
Concept of plant nutrition
? Complex interactions involving
weathering（风化） of rock minerals,
decaying(腐解） of organic matter,
such as humus and residues of
plant,animals,and microbes,take
place to form inorganic minerals in
soil,
? Roots absorb mineral nutrients as
ions in soil water,Many factors
influence nutrient uptake for
plants,
? This interrelationship involves a
complex balance of mineral
elements essential and beneficial
for optimum plant growth.
Concept of plant nutrition
Essential elements
? The material of living plants consist
of organic matter,water and
minerals,The percentage distribution
of these three components is in the
following order of magnitude:
? Water 70%(fresh matter)
? Organic material 27%(fresh matter)
? Minerals 3% (fresh matter)
? The term essential mineral
element (or mineral nutrient) was
proposed by Arnon and Stout
(1939),
? They concluded three criteria(标
准 ) must be met for an element
to be considered essential(必需的 ).
Essential elements
Three criteria of Essential elements
? 1,A plant must be unable to
complete its life cycle in the absence
of the mineral element,
? 2,The function of the element must
not be replaceable by another
mineral element,or deficiency
symptoms can not be remedied by
supplying some other element
? 3,The element must be directly
involved in plant metabolism.
Sixteen Essential Elements
Carbon (C) Hydrogen (H) Oxygen (O)
Nitrogen (N) Phosphorus (P) Potassium (K)
Calcium (Ca) Magnesium (Mg) Sulfur (S)
Iron (Fe) Manganese (Mn) Copper (Cu)
Zinc (Zn) Molybdenum (Mo) Boron (B)
Chlorine (Cl)
Nutrient Composition of Plants
Relative amounts of essential elements in plant tissues
Two ways to classify the essential elements
1,Classified by whether it is used in large or
small amounts
(Macronutrients or micronutrients)
2,Classified by its function in the plant
(What the element does in the plant)
Macronutrients and Micronutrients
A,Macronutrients are elements that are used in
relatively large amounts (% or g/kg).
B,Micronutrients are elements that are used in
relatively small amounts (μ g/g or mg/kg).
The concentration of macronutrients in plant
tissue is often more than 1000x greater than
the concentration of micronutrients.
Carbon (C) Hydrogen (H) Oxygen (O)
Nitrogen (N) Phosphorus (P) Potassium (K)
Calcium (Ca) Magnesium (Mg) Sulfur (S)
? N,P,and K are called primary macronutrients
? Ca,Mg,and S are called secondary
macronutrients
Macronutrients
Micronutrients
Iron (Fe) Manganese (Mn) Copper (Cu)
Zinc (Zn) Molybdenum (Mo) Boron (B)
Chlorine (Cl)
表 1-1 正常生长的植株中营养元素的平均含量（ Stout,P.R.）
元素 干物质中的含量 相当于钼原
子数的倍数μmol/g μg/g %
Mo 0.001 0.1 1
Cu 0.10 6.0 100
Zn 0.30 20 300
Mn 1.0 50 1000
B 2.0 20 2000
Fe 2.0 100 2000
CI 3.0 100 3000
S 30 0.1 30000
P 60 0.2 60000
Mg 80 0.2 80000
Ca 125 0.5 125000
K 250 1.0 250000
N 1000 1.5 1000000
O 30000 45 30000000
C 40000 45 40000000
H 60000 6 60000000
Concentrations of essential elements in leaves
s uga r c a ne r i c e c or n S oyb e a n
ma c r onu t r i e nt s %
N i t r oge n 1,5 2,5 3,0 4,0
P ot a s s i um 2,2 1,0 1,9 1,7
P hos pho r u s 0,05 0,1 0,25 0,26
M a gne s i um 0,1 0,1 0,25 0,25
S ul f ur 0,1 0,1 0,2 0,25
C a l c i um 0,1 0,15 0,15 0,15
m i c r onu t r i e nt s p pm
I r on 10 70 15 50
C hl or i ne 20 25
M a nga ne s e 20 20 15 20
Z i nc 10 10 15 20
B or on 1 3 10 20
C opp e r 2 5 5 10
S i l i c on 5
M ol ybd e num < 0,1 < 0,1 0,1 0,7
Data,represent the lowest concentrations found in recently matured leaves of healthy plants.
Higher levels are commonly found
? Among the all of nutrients,N,P and K are
three most important ones in crops
production because the amount of plant
required is bigger but their availability are
lower in the soil,so they are often
deficiency to crop in the field,and they are
needed to compensated by fertilizers,
Three primary fertilizers (肥料三要素）
or primary macronutrients
表 1-2几种作物每吨生物量所需的 N,P2O5和 K2O（ kg）
Requirement of N,P2O5 and K2O of some kinds of crops (kg/tone biomass)
作物 N P2O5 K2O
黑麦 40 15 44
春小麦 47 15 41
冬小麦 51 15 39
大麦 36 14 38
多年生牧草 29 13 38
晚马铃薯 9 3 11
菜豆 6 2 8
大白菜 6 3 12
黄瓜 5 2 8
番茄 5 2 5
芜箐
Crop
Base
Yield
tonnes/h
a Estimated Nutrient Removal kg/ha
Corn 9.1 135 68 47
Wheat 5 118 49 30
Wheat+straw 5 165 59 138
Soybeans 3 217 47 78
Canola 2.5 106 62 30
Cotton
(seed+lint) 1.7 45 11 14
Sugar beets 50 20 250 40
Nutrient Removal by Crops
N P2O5 K2O
Factors that affect the mineral content in the plant
1,Genotypes,Ability of the plant to take up
nutrients
2,Availability of the nutrient in the soil or water
etc.
3,Portion of the plant (leaf compared to fruit)
4,Age of the plant
The special functions of the element must not be
replaceable by another mineral element
营养元素的同等重要律与不可代替律
? No matter how much is required by
the plant,or how much content is it
in plant,the every essential element
is same important to the plant
physiology and plant growth; its
function of every essential element
cannot substitute by another mineral
element completely.
? Beneficial elements are those that can
compensate for toxic effects of other
elements or may replace mineral nutrients
in some other less specific function such
as the maintenance of osmotic pressure.
? The beneficial elements have not been
deemed essential for all plants but may be
essential for some,
Beneficial elements
? Cobalt for instance is essential for
nitrogen fixation in legumes,
? Silicon,Equisetum（木贼属） and many
grasses (particularly rice) require silicon,
deposited in cell walls,has been found
to improve heat and drought(干旱 )
tolerance and increase resistance to
insects and fungal infections,
Beneficial elements
Silicon,acting as a beneficial
element,can help compensate for toxic
levels of manganese,iron,sodium and
aluminum as well as zinc deficiency.
Na is required by species using the
C4 pathway of photosynthesis,Where it
is supposed to maintain the integrity of
chloroplasts and thus allow the uptake
of pyruvate（丙酮酸）
Beneficial elements
? Plant nutrients and toxins are important
components of food chains that begin with
plants and include animals-wild,domestic,
and human
? Deficiencies of the essential elements
frequently limit plant growth or quality,Even
when the plants themselves do not suffer from
a deficiency,they sometimes provide animals
with a diet deficient in certain elements,for
example,Mo,Se,Co,Cu,P,Na,Ca,or I
Essential elements and food chain
Essential elements and food chain
? A more holistic approach(整体分析）
to plant nutrition would not be
limited to nutrients essential to
survival but would include mineral
elements at levels beneficial for
optimum growth and food chain,
More toxic element
? Plants frequently contain unnecessary
high and sometimes toxic
concentrations of an essential or
nonessential element,Most commonly
toxic to plant are AI and Mn (in acid
soils),Na,and CI (in saline soils),
boron,and copper,
? Elements such as copper,lead,arsenic,
cadmiun,molybdenum,and selenium
are sometimes present at
concentrations that injure foraging
animals,though the plant itself is little
affected,
Phytoremediation (植物修复）
? Plant are very adaptive(适应性 )
? The plants,which can uptake and
accumulation high level metal,is known
as hyperaccumulators,
? Now 45 plant families are known to
contain metal-accumulating species.
? The decontamination（净化） of soil by
means of plants uptake of organic and /or
inorganic contaminants is called
phytoremediation,
Specific function
Structural components结构物质 (C,H,O,N,P,S)
Enzymes activators 酶活化剂 (K,Ca,Mg,Mn,Zn)
Redox reaction 氧化反应 (Fe,Cu,Mn,Mo)
Elements of uncertain function未知功能 (B,CI)
The function of essential nutrients
NON-SPECIFIC OSMOTIC FUNCTIONS
The generation of turgor（膨压） in walled cells depends on
the accumulation of inorganic and organic solutes within the
vacuoles（液泡） and cytoplasm（原生质） of plant
K+ is energetically much cheaper than organic solutes,Indeed
K+ is typically the preferred cation（阳离子） for turgor
generation in land plants.
For halophytes（盐生植物）,NaCl is an important
osmoticum（渗透物质） but it is restricted to the vacuole
The function of essential nutrients
C,H,O,N,and S are the major components of the
plant tissue,Essential elements of atomic groups
which are involved in enzymic processes
P,B,and Si are important in esterfication (酯化作
用 )processes,P esters are involved in the energy
transfer reactions
Classified by function
Classified by function
K,Na,Mg,Ca,Mn,and Cl control the
movement of water and ions between
cells,Non-special functions (osmotic
potentials) and special function
(enzyme activation)
Fe,Cu,Zn,and Mo enable electron
transport by valency change.
2,Flow of the nutrients from
soil to the root
N u trie n t u p t a ke s te p s
nu t
M ove m en t t h r o ug h so il
C ell w all C ell m embran e
C ell to cell tran sp ortvascu l a r tissue
un loa d i n g
nutrient
How do plant roots and nutrients come into contact?
Root interception
离子代换或截获
Mass flow
质流
Diffusion
扩散
Root Interception(截获）
Roots grow through soil
and come into contact
with the surfaces of soil
particles,The root
surfaces are able to take
up the nutrients from soil
clay mineral,
离子代换
Root Interception
Roots only occupy about 1-2% of the
total soil volume,so the amount of
nutrients take up in this way is relatively
small,
But It is most significant for,
1.High concentrations in soil solution such as
Ca and Mg(?)
2.Nutrients required in small amounts (e.g,Zn,
Mn,and other micronutrients)
Mass Flow (or bulk flow)质流
Nutrients are transported as water
moves from the soils to the plant
roots.
or soil solution
(containing dissolved
nutrients) moves down
gradients of water potential
水吸力 毛管力
根压
? The characteristics of mass flow
? Wet soil ? dry soil
? Higher water potential ?lower water potential
? All nutrients move in the same direction
? Rate of nutrient movement depends on
– concentration in solution - affected by uptake and
replacement
– volume of solution - affected by soil moisture and
by soil pore sizes
– rate of flow - affected by transpiration(蒸腾）,
evaporation（蒸发） and drainage（排水）
Mass Flow (or bulk flow)质流
Mass flow supplies most of the required
amounts of NO3-,SO42-,Cl-,and H3BO3
It often supplies more than the required
amounts of Ca,Mg.
It can meet or supply a significant portion of
the requirements for Cu,Mn,and Mo.
Mass Flow (or bulk flow)质流
Factors that affect nutrient transport by mass flow
1,Soil water content – if the soil is dry water
move very slowly.
2,Temperature– if the temperature is low,
water uptake by the plant is reduced and
nutrient transport declines,
3,Air humid
Diffusion(扩散）
Diffusion occurs
when an ion is
transported from a
place of higher
concentration to a
place of lower
concentration.
Diffusion
As plants take up nutrients,there is a
reduction in the nutrient concentration near
to the root (rhizosphere),So the nutrient
concentration in bulk soil solution is higher
then that in rhizosphere,then nutrients will
begin to move into the area near to the root
surface,
Nutrient concentration is different at the root surface compared
to the soil solution,If the difference in the concentration is
very large,then diffusion can occur more rapidly,Diffusion is
an important mechanism for the movement of NH4+,P,K,Fe,
and Zn,
图２根系附近土壤养分耗竭模式
Canola 油菜Corn 玉米
Diffusion of nutrients
? Movement in solution is independent of direction
of flow of solution
? Nutrient moves down concentration gradient
? Rate for each nutrient depends on
– concentration gradient (driving force)
– diffusion coefficient in soil (D) (ease of movement)
– D=Di Φf ╳ Dcs/Dc
– Diffusion coefficient in water (Di)
– buffering capacity of soil (Dcs/Dc)
– tortuosity of pathway in soil (f)
– soil moisture (continuity of water-filled pores)(Φ)
Di = diffusion coefficient of ions in soil (m2 s-1)
ion wet soil
-10 kPa
dry soil
-1000 kPa
NO3-
(low buffering capacity)
10-9 10-11
K+ 10-11 10-13
H2PO4-
(high buffering capacity)
10-13 10-15
values are much lower than for diffusion in pure water(0.5-2.0 ╳ 10-9)due
to,
? tortuosity(曲折度 ) of pathway
? increased viscosity(粘滞性） close to surfaces
? exclusion（排斥） of ions by surface charge on particles
Processes involved in nutrient replacement
replacement at root surface N P
diffusion rapid slow
mass flow +++ (+)
N has low buffering capacity and high
concentration in soil solution
N is VERY MOBILE (easily gets to roots; easily
leached out of soil)
P has high buffering capacity and low
concentration in soil solution (<10μM)
P is VERY IMMOBILE
1
23soil
根
shoot
1,Root interception; 2,diffusion; 3,mass flow
root
