Watch a Kansas Wheat Field Grow!

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

PLANT NUTRITION

Watch a Japanese Rice Field Grow!

Rice: Eastern China & Northern India 7,000 years ago

441.0 million Metric Tons 2008/09 global rice production is projected

Visit the Iowa Corn Cam!

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).

• 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 sourceof carbon for

Photosynthesis,diffuses into

leaves from theair through

stomata.Throughstomata, leavesexpel H2O andO2.

H2O

O2

CO2

Roots take inO2 and expelCO2. The plantuses O2 for cellularrespiration but is a net O2 producer.

O2

CO2

H2O

Roots absorbH2O and

minerals fromthe soil.

Minerals

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

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.

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.

Control: Solutioncontaining all minerals

Experimental: Solutionwithout potassium

APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants.

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)

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)

CuMn CoZn MoB(y)!

• 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

Phosphate-deficient

Healthy

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

Figure 37.5

The A horizon is the topsoil, a mixture ofbroken-down rock of various textures, living organisms, and decaying organic matter.

The B horizon contains much less organicmatter than the A horizon and is lessweathered.

The C horizon, composed mainly of partiallybroken-down rock, serves as the “parent”material for the upper layers of soil.

A

B

C

http://www.dnr.state.oh.us/soilandwater/soils/soilreg1.htmhttp://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

• The film of loosely bound water– Is usually available

to plants

(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.

Soil particle surrounded byfilm of water

Root hair

Water available to plant

Air space

• Acids derived from roots contribute to a plant’s uptake of minerals

– When H+ displaces mineral cations from clay particles

(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.

H2O + CO2 H2CO3 HCO3– +

Root hair

K+

Cu2+Ca2+

Mg2+K+

K+

H+

H+

Soil particle–

– – –– – – –

–

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

                                      

International Fertilizer Industry Association

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

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.

Recent estimates indicate 70% of all Nitrogen within Nitrogen Cycle on Earth is currently contributed by human activity!

Death in the Gulf

• 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

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)NH4

+

(ammonium)

H+

(From soil)

NO3–

(nitrate)Nitrifyingbacteria

Denitrifyingbacteria

Root

NH4+

Soil

AtmosphereNitrate and nitrogenous

organiccompoundsexported in

xylem toshoot system

Ammonifyingbacteria

• 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

(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.

Nodules

Roots

• 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 noduleInfectionthread

Rhizobiumbacteria

Dividing cellsin root cortex

Bacteroid

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.

Bacteroid

Bacteroid

Developingroot nodule

Dividing cells in pericycleInfected

root hair1

2

3

Nodulevasculartissue

43 Growth continues in the

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

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.

1

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.

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

a Ectomycorrhizae. 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.

Mantle(fungal sheath)

Epidermis Cortex Mantle(fungalsheath)

Endodermis

Fungalhyphaebetweencorticalcells (colorized SEM)

100 m(a)

• In endomycorrhizae

– Microscopic fungal hyphae extend into the root

Epidermis Cortex

Fungalhyphae

Roothair

10 m

(LM, stained specimen)

Cortical cells

Endodermis

Vesicle

Casparianstrip

Arbuscules

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.

(b)

• Farmers and foresters

– Often inoculate seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae

Staghorn fern, an epiphyte

EPIPHYTES

PARASITIC PLANTS

CARNIVOROUS PLANTS

Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite

Host’s phloem

Haustoria

Indian pipe, a nonphotosynthetic parasite

Venus’ flytrapPitcher plants Sundews

Dodder

Epiphytes, Parasitic Plants, and Carnivorous PlantsSome plants

Have nutritional adaptations that use other organisms in nonmutualistic ways