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PLANT NUTRITION
Development of Agriculture critical to civilization
Top three major human foods are grass seeds/fruit (grains)
Wheat: Near East 9,000 years ago
684.4 million Metric Tons 2008/09 global wheat production
is projected
Watch a Kansas Wheat Field Grow!
Rice: Eastern China & Northern India 7,000 years ago
441.0 million Metric Tons 2008/09 global rice production is
projected
Watch a Japanese Rice Field Grow!
Corn: Central Mexico 5,500 years ago
772 million metric tons 2008/09 global corn production
is projected (U.S. ethanol is consuming
roughly 13% of the corn produced in the world).
Visit the Iowa Corn Cam!
• Overview: A Nutritional Network
• Every organism
– Continually exchanges energy and materials
with its environment
• For a typical plant
– Water and minerals come from the soil, while
carbon dioxide comes from the air
• The branching root system and shoot system
of a vascular plant
– Ensure extensive networking with both
reservoirs of inorganic nutrients
• Plants require certain
chemical elements to
complete their life cycle
• Plants derive most of
their organic mass from
the CO2 of air
H2O
CO2
O2
CO2, the source
of carbon for
Photosynthesis,
diffuses into
leaves from the
air through
stomata.
Through
stomata, leaves
expel H2O and
O2.
– But they also depend
on soil nutrients such
as water and
minerals
Roots take in
O2 and expel
CO2. The plant
uses O2 for cellular
respiration but is
a net O2 producer.
O2
Minerals
Roots absorb
H2O and
minerals from
the soil.
CO2
H2O
Macronutrients and Micronutrients
• More than 50 chemical elements
– Have been identified among the inorganic
substances in plants, but not all of these are
essential
• A chemical element is considered essential
– If it is required for a plant to complete a life
cycle
• Researchers use hydroponic culture
– To determine which chemicals elements are
essential
APPLICATION
In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is
to identify essential elements in plants.
TECHNIQUE
Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides the
roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is essential.
Control: Solution
containing all minerals
Experimental: Solution
without potassium
RESULTS
If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and
discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral
deficiencies in soil.
Criteria of essentiality (DI Arnon & PR Stout, 1939)
1. The element must be essential for normal growth or
reproduction, which can not proceed without it.
2. The element cannot be replaced by another
element.
3. The requirement must be direct, that is, not the
result of some indirect effect such as relieving
toxicity caused by some other substance.
C HOPKNS CaFe Mg Na Cl
(Mighty good)
(Not always) (Clean)
CuMn CoZn MoB(y)!
With some apologies to Edward Hopper (American 1882-1967) Nighthawks, 1942
Oil on canvas; 33 1/8 x 60 in. (84.1 x 152.4 cm)
• Nine of the essential elements are called
macronutrients
– Because plants require them in relatively large
amounts
• The remaining eight essential elements are
known as micronutrients
– Because plants need them in very small
amounts
Key to role elements play in plants for next two slide
Structual
Cofactors, osmotic relationships
C = carbon = Major structural component of organic molecules
H = Hydrogen = Major structural component of organic molecules
O = Oxygen = Major structural component of organic molecules; Final
electron acceptor in Oxidative Phosphorylation
P = Phosphorus = Important structural component of nucleic acids,
phospholipids, coenzymes
K = Potassium = Important cofactor of some enzymes, stomatal opening,
membrane potentials, osmotic balance
N = Nitrogen = Important structural component of nucleic acids, proteins,
chlorophyll, some phytohormones
S = Sulfer = Important structural component of some amino acids, forms
disulfide bridges that are important to enzyme activity
Fe = Iron = Site of catalytic reaction in many redox enzymes, essential for
chlorophyll formation
Mg = Magnesium = Involved in stabilization of ribosomes, cofactor for
many enzymes, structural component of chlorophyll
Na = Sodium = Beneficial to Halophytes (Mangrove, Atriplex, etc)
Cl = Chlorine = Involved in photolysis of water in photosynthesis
Cu = Copper = site of catalytic reaction for some enzymes
Mn = Manganese = Respiratory enzyme cofactor, involved in photolysis of
water, required for auxin synthesis
Co = Cobalt = Structural component of vitamin B12, necessary for nitrogen
fixation
Zn = Zinc = Involved in auxin synthesis, enzyme cofactor
Mo = Molybdemun = Involved in reduction of nitrates
B = Boron = Involved in translocation and absorption of sugar, interacts
with Ca flux
Structual
Cofactors, osmotic relationships
• Essential elements in plants
Symptoms of Mineral Deficiency
• The symptoms of mineral deficiency
– Depend partly on the nutrient’s function
– Depend on the mobility of a nutrient within the
plant
• Deficiency of a mobile nutrient
– Usually affects older organs more than young
ones
• Deficiency of a less mobile nutrient
– Usually affects younger organs more than
older ones
• The most common deficiencies
– Are those of nitrogen, potassium, and
phosphorus
Healthy
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
• Soil quality is a major determinant of plant
distribution and growth
• Along with climate
– The major factors determining whether particular
plants can grow well in a certain location are the
texture and composition of the soil
• Texture
– Is the soil’s general structure
• Composition
– Refers to the soil’s organic and inorganic chemical
components
Texture and Composition of Soils
• Various sizes of particles derived from the
breakdown of rock are found in soil
– Along with organic material (humus) in various
stages of decomposition
• The eventual result of this activity is topsoil
– A mixture of particles of rock and organic
material
• The topsoil and other
distinct soil layers, or
horizons
–
Are often visible in
vertical profile where
there is a road cut or
deep hole
The A horizon is the topsoil, a mixture of
broken-down rock of various textures, living
organisms, and decaying organic matter.
A
B
The B horizon contains much less organic
matter than the A horizon and is less
weathered.
C
The C horizon, composed mainly of partially
broken-down rock, serves as the “parent”
material for the upper layers of soil.
http://www.dnr.state.oh.us/soilandwater/soils/soilreg1.htm
http://www.delawareswcd.org/soilsurvey/soilsdescriptions.htm
Soils in the Miamian series, for example, are well drained. They typically have a very dark grayish brown to brown silt loam or loam
topsoil layer ("A horizon") 5 to 10 inches thick. They commonly have a brown or yellowish brown subsoil layer ("B horizon"), 8 to 35
inches thick, with a higher clay content than the A horizon. Below the subsoil, soils in the Miamian series have a brown to light olive
brown substratum ("C horizon") that is slightly or moderately alkaline and has a lower clay content than the B horizon.
• After a heavy rainfall,
water drains away
from the larger spaces
of soil
– But smaller spaces
retain water because
of its attraction to
surfaces of clay and
other particles
Soil particle surrounded by
film of water
Root hair
Water available to
plant
• The film of loosely
bound water
– Is usually available
to plants
Air space
(a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly
held by hydrophilic soil particles. Water bound less tightly to soil particles can be
absorbed by the root.
• Acids derived from roots contribute to a plant’s
uptake of minerals
– When H+ displaces mineral cations from clay
particles
Soil particle
K+
–
–
Cu2+
–
–
K+
–
–
–
Mg2+
– +
K
–
Ca2+
H+
H2O + CO2
H2CO3
HCO3– + H+
Root hair
(b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients
available by displacing positively charged minerals (cations such as
Ca2+) that were bound tightly to the surface of negatively charged
soil particles. Plants contribute H+ by secreting it from root hairs
and also by cellular respiration, which releases CO2 into the soil
solution, where it reacts with H2O to form carbonic acid (H2CO3).
Dissociation of this acid adds H+ to the soil solution.
Soil Conservation and Sustainable Agriculture
• In contrast to natural ecosystems
– Agriculture depletes the mineral content of the
soil, taxes water reserves, and encourages
erosion
• The goal of soil conservation strategies
– Is to minimize this damage
Fertilizers
• Commercially produced fertilizers
– Contain minerals that are either mined or
prepared by industrial processes
• “Organic” fertilizers
– Are composed of manure, fishmeal, or
compost
All fertilizer labels have three bold
numbers. The first number is the
amount of nitrogen (N), the second
number is the amount of phosphate
(P2O5) and the third number is the
amount of potash (K2O). These
three numbers represent the primary
nutrients (nitrogen(N) phosphorus(P) - potassium(K)).
This label, known as the fertilizer
grade, is a national standard.
A bag of 10-10-10 fertilizer contains
10 percent nitrogen, 10 percent
phosphate and 10 percent potash.
A Homeowner's Guide to Fertilizer
International Fertilizer Industry Association
Recent estimates indicate 70% of all Nitrogen within Nitrogen
Cycle on Earth is currently contributed by human activity!
Death in the Gulf
Hypoxia means an absence of oxygen reaching living tissues. In coastal waters, it is characterized by low levels of
dissolved oxygen, so that not enough oxygen is available to support fish and other aquatic species.
Nutrients, such as nitrogen and phosphorous, are essential for healthy marine and freshwater environments.
However, an over overabundance of nutrients can trigger excessive algal growth (or eutrophication) which results in
reduced sunlight, loss of aquatic habitat, and a decrease in oxygen dissolved in the water.
Excess nutrients may come from a wide range of sources:
Runoff from developed land
Atmospheric deposition
Soil erosion
Agricultural fertilizers
Sewage and industrial discharges also contribute nutrients.
• Nitrogen is often the mineral that has the
greatest effect on plant growth
• Plants require nitrogen as a component of
– Proteins, nucleic acids, chlorophyll, and other
important organic molecules
Soil Bacteria and Nitrogen Availability
• Nitrogen-fixing bacteria convert atmospheric N2
– To nitrogenous minerals that plants can absorb as
a nitrogen source for organic synthesis
Atmosphere
N2
N2
Atmosphere
Soil
N2
Nitrogen-fixing
bacteria
Denitrifying
bacteria
H+
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
(From soil)
Soil
+
NH4
NH3
(ammonia)
–
+
NH4
(ammonium)
Nitrifying
bacteria
NO3
(nitrate)
Ammonifying
bacteria
Organic
material (humus)
Root
• Plant nutritional adaptations often involve
relationships with other organisms
• Two types of relationships plants have with
other organisms are mutualistic
– Symbiotic nitrogen fixation
– Mycorrhizae
The Role of Bacteria in Symbiotic Nitrogen Fixation
• Symbiotic relationships with nitrogen-fixing
bacteria
– Provide some plant species with a built-in
source of fixed nitrogen
• From an agricultural standpoint
– The most important and efficient symbioses
between plants and nitrogen-fixing bacteria
occur in the legume family (peas, beans, and
other similar plants)
• Along a legumes possessive roots are swellings
called nodules
– Composed of plant cells that have been “infected”
by nitrogen-fixing Rhizobium bacteria
Nodules
Roots
(a) Pea plant root. The bumps on
this pea plant root are nodules
containing Rhizobium bacteria.
The bacteria fix nitrogen and
obtain photosynthetic products
supplied by the plant.
• The bacteria of a nodule
– Obtain sugar from the plant and supply the
plant with fixed nitrogen
• Each legume
– Is associated with a particular strain of
Rhizobium
• Development of a soybean root nodule
1 Roots emit chemical
signals that attract
Rhizobium bacteria.
The bacteria then emit
signals that stimulate
root hairs to elongate
and to form an infection
thread by an
invagination of the
plasma membrane.
Infection
thread
Rhizobium
bacteria
Dividing cells
in root cortex
Bacteroid
Infected
root hair
Dividing cells in
pericycle
1
2
2 The bacteria penetrate the
cortex within the Infection
thread. Cells of the cortex
and pericycle begin
dividing, and vesicles
containing the bacteria bud
into cortical cells from the
branching infection thread.
This process results in the
formation of bacteroids.
Developing
root nodule
3
3 Growth continues in the
affected regions of the
cortex and pericycle, and
these two masses of
dividing cells fuse,
forming the nodule.
4
4 The nodule develops
vascular tissue that
supplies nutrients to the
nodule and carries
nitrogenous compounds
into the vascular
cylinder for distribution
throughout the plant.
Bacteroid
Bacteroid
Nodule
vascular
tissue
The Molecular Biology of Root Nodule Formation
• The development of a nitrogen-fixing root
nodule
– Depends on chemical dialogue between
Rhizobium bacteria and root cells of their
specific plant hosts
Symbiotic Nitrogen Fixation and Agriculture
• The agriculture benefits of symbiotic nitrogen
fixation
– Underlie crop rotation
• In this practice
– A non-legume such as maize is planted one
year, and the following year a legume is
planted to restore the concentration of nitrogen
in the soil
Mycorrhizae and Plant Nutrition
• Mycorrhizae
– Are modified roots consisting of mutualistic
associations of fungi and roots
• The fungus
– Benefits from a steady supply of sugar donated by
the host plant
• In return, the fungus
– Increases the surface area of water uptake and
mineral absorption and supplies water and
minerals to the host plant
The Two Main Types of Mycorrhizae
• In ectomycorrhizae
– The mycelium of the fungus forms a dense sheath
over the surface of the root
Epidermis
a Ectomycorrhizae. The mantle
(a)
of the fungal mycelium
ensheathes the root. Fungal
hyphae extend from the mantle
into the soil, absorbing water
and minerals, especially
phosphate. Hyphae also
extend into the extracellular
spaces of the root cortex,
providing extensive surface
area for nutrient exchange
between the fungus and its
host plant.
Cortex
Mantle
(fungal
sheath)
100 m
Endodermis
Mantle
(fungal sheath)
Fungal
hyphae
between
cortical
cells
(colorized SEM)
• In endomycorrhizae
– Microscopic fungal hyphae extend into the root
(b)
2 Endomycorrhizae. No mantle
forms around the root, but
microscopic fungal hyphae
extend into the root. Within
the root cortex, the fungus
makes extensive contact with
the plant through branching of
hyphae that form arbuscules,
providing an enormous
surface area for nutrient
swapping. The hyphae
penetrate the cell walls, but
not the plasma membranes,
of cells within the cortex.
Epidermis
Cortex
Cortical cells
10 m
Endodermis
Fungal
hyphae
Vesicle
Casparian
strip
Root
hair
Arbuscules
(LM, stained specimen)
• Farmers and foresters
– Often inoculate seeds with spores of
mycorrhizal fungi to promote the formation of
mycorrhizae
Epiphytes, Parasitic Plants, and Carnivorous Plants
EPIPHYTES
Some plants
Have nutritional adaptations
that use other organisms
in nonmutualistic ways
Staghorn fern, an epiphyte
PARASITIC PLANTS
Host’s phloem
Dodder
Haustoria
Mistletoe, a photosynthetic parasite
Dodder, a nonphotosynthetic
parasite
Indian pipe, a nonphotosynthetic parasit
CARNIVOROUS PLANTS
Venus’ flytrap
Pitcher plants
Sundews