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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!.

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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

But they also depend on soil nutrients such as water and minerals




CO2, the source

of carbon for


diffuses into

leaves from the

air through



stomata, leaves

expel H2O and


Roots take in

O2 and expel

CO2. The plant

uses O2 for cellular

respiration but is a net O2 producer.




Roots absorb

H2O and

minerals from

the soil.


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

Macronutrients and Micronutrients
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)

  • The element must be essential for normal growth or reproduction, which can not proceed without it.
  • The element cannot be replaced by another element.
  • The requirement must be direct, that is, not the result of some indirect effect such as relieving toxicity caused by some other substance.


(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


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


Cofactors, osmotic relationships

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

Symptoms of Mineral Deficiency
  • 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





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


Is the soil’s general structure


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

Texture and Composition of Soils
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.


The B horizon contains much less organic

matter than the A horizon and is less




The C horizon, composed mainly of partially

broken-down rock, serves as the “parent”

material for the upper layers of soil.

Figure 37.5


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

The film of loosely bound water

Is usually available to plants

Soil particle surrounded by

film of water

Root hair

Water available to plant

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








HCO3– +


H2O + CO2


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 hairsand 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

Soil Conservation and Sustainable Agriculture
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





Nitrate and nitrogenousorganiccompoundsexported inxylem toshoot system





H+ (From soil)


NH3 (ammonia)


NO3– (nitrate)

NH4+ (ammonium)



Organicmaterial (humus)


Soil Bacteria and Nitrogen Availability
Plant nutritional adaptations often involve relationships with other organisms

Two types of relationships plants have with other organisms are mutualistic

Symbiotic nitrogen fixation


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)

The Role of Bacteria in Symbiotic Nitrogen Fixation
Along a legumes possessive roots are swellings called nodules

Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria



(a) Pea plant root. The bumps onthis pea plant root are nodules containing Rhizobium bacteria.The bacteria fix nitrogen and obtain photosynthetic productssupplied 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



Dividing cellsin root cortex


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.

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.


Dividing cells in pericycle

Infectedroot hair



Developingroot nodule



3Growth continues in the affected regions of the cortex and pericycle, and these two masses of dividing cells fuse, forming the nodule.



The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant.



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

The Molecular Biology of Root Nodule Formation
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

Symbiotic Nitrogen Fixation and Agriculture
mycorrhizae and plant nutrition

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

Mycorrhizae and Plant Nutrition
the two main types of mycorrhizae
In ectomycorrhizae

The mycelium of the fungus forms a dense sheath over the surface of the root




aEctomycorrhizae. The mantle 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.


100 m



Mantle(fungal sheath)

(colorized SEM)

The Two Main Types of Mycorrhizae
In endomycorrhizae

Microscopic fungal hyphae extend into the root




10 m

2Endomycorrhizae. 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.

Cortical cells







(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


Staghorn fern, an epiphyte


Host’s phloem



Mistletoe, a photosynthetic parasite

Indian pipe, a nonphotosynthetic parasite

Dodder, a nonphotosynthetic parasite


Venus’ flytrap


Pitcher plants

Epiphytes, Parasitic Plants, and Carnivorous Plants

Some plants

Have nutritional adaptations that use other organisms in nonmutualistic ways