1. Chapter 37
Plant Nutrition

2. Nutrient Reservoirs
Every organism continually exchanges energy and materials with its environment
For plants…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

3. Macronutrients and Micronutrients
Plants derive most of their organic mass from the CO2 of air but they also depend on soil nutrients
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

4. How would you identify an essential nutrient?
Hydroponic culture can be used 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: Solution
containing all minerals
Experimental: Solution
without 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.

5. Macronutrients and Micronutrients
Nine of the essential elements are called macronutrients because plants require them in relatively large amounts
C, O, H, N, K-Primary
Ca, Mg, P, S -Secondary
The remaining eight essential elements are known as micronutrients because plants need them in very small amounts
Cl, Fe, Zn, Mn, B, Cu, Mo

6. Primary Macronutrients
Nitrogen: Absorbed usually as NO3 or NH3
Essential for vegetable growth
Deficiency causes Chlorosis
Phosphorous: Usually absorbed as PO4
Used in protein and nucleic acid production
Deficiency causes purpling
Potassium: (K) introduced through inorganic salts
Maintains regular cell function
Present in older plants moreso than younger—marginal firing of leaves

7. Secondary Macronutrients
Calcium: (Ca2+)
Essential to mitosis
Deficiency causes malformed buds and no root growth
Magnesium: (Mg+2)
Used in the creation of fats and sugars
Deficiency causes yellowing between veins
Sulfur: Usually absorbed as sulfate (SO42-)
Used in formation of amino acids and taste of veg
Deficiency causes chlorate foliage

8. Micronutrients Boron: (B) Iron: (Fe) Manganese: (Mn+2)
Essential for mitosis
Death of buds if deficient
Iron: (Fe)
Component of chlorophyll
Deficiency causes death of younger leaves
Manganese: (Mn+2)
Used in synthesis of chlorophyll
Deficiency leads similar to iron

9. Cont… Zinc :Zn Copper: Cu2+ Chlorine: Cl Enzyme activator
Deficiency causes reduced leaf size
Copper: Cu2+
Chlorophyll synthesis
Deficiency stunts plants and kills leaves
Chlorine: Cl
Difficult to have deficiency
Stunting and necrosis can occur from chlorine excess

10. Essential elements in plants

11. 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 (young tissue can more efficiently draw minerals to it)
Deficiency of a less mobile nutrient
Usually affects younger organs more than older ones (older tissue has a store of minerals to fall back on when the mineral is in short supply)

12. Mineral Deficiency The most common deficiencies
Are those of nitrogen, potassium, and phosphorus
Phosphate-deficient
Healthy
Potassium-deficient
Nitrogen-deficient
Reddish-purple margins esp. on young leaves
“Firing”…drying along tips and margins of older leaves
Yellowing that starts at the tip and moves along the center of older leaves

13. Soil Characteristics
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 (sandy, clayey, etc)
Composition…refers to the soil’s organic and inorganic chemical components
Various sizes of particles derived from the breakdown of rock are found in soil along with organic material (humus) in various stages of decomposition
Topsoil… is the mixture of particles of rock and organic material

14. Soil Horizons
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
weathered.
The C horizon, composed mainly of partially
broken-down rock, serves as the “parent”
material for the upper layers of soil. A B C

15. Availability of Soil Water
After a 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 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 by
film of water
Root hair
Water available to plant
Air space

16. Cation Exchange
Acids derived from roots contribute to a plant’s uptake of minerals when H+ displaces mineral cations from clay particles
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.
H2O + CO2
H2CO3
HCO3– +
Root hair K+
Cu2+
Ca2+
Mg2+ H+
Soil particle –

17. Agriculture Conventional agriculture Sustainable agriculture
In contrast to natural ecosystems agriculture depletes the mineral content of the soil, taxes water reserves, and encourages erosion
Sustainable agriculture
Is ecologically sound
Is economically viable
Is socially just
Is humane.

18. Fertilizers
Commercially produced fertilizers contain minerals that are either mined or prepared by industrial processes
“Organic” fertilizers are composed of manure, fishmeal, or compost

19. Irrigation
Is a huge drain on water resources when used for farming in arid regions
Can change the chemical makeup of soil
Salinization (salt buildup)
sprinkler
drip
Ditch…trench

20. Erosion Topsoil from thousands of acres of farmland
Is lost to water and wind erosion each year in the United States
The U.S. Soil Conservation Service reports that more than 4 million acres of cropland are being lost to erosion in this country every year. That's an area greater than the size of Connecticut. Our annual topsoil loss amounts to 7 billion tons. That is 60,000 pounds for each member of the population.
Erosion on conventionally tilled field

21. Prevention of topsoil loss
Strip cropping: practice of growing field crops in narrow strips either at right angles to the direction of the prevailing wind, or following the natural contours of the terrain to prevent wind and water erosion of the soil
Contour tillage (slows water runoff and erosion)

22. Prevention of topsoil loss
Conservation tillage (Min-till)
Terraces
A minimum tillage system may involve quicker and fewer passes at a shallower depth
Cover Crops
Cover crop in an orchard
Cover crop in vegetable garden

23. Soil Reclamation Some areas are unfit for agriculture
Because of contamination of soil or groundwater with toxic pollutants
Phytoremediation: is a biological, nondestructive technology that seeks to reclaim contaminated areas by using the ability of some plants to remove soil pollutants

24. Nitrogen
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 a host of other important organic molecules

25. 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
Nitrogen-fixing bacteria
Organic material (humus)
NH3 (ammonia)
NH4+ (ammonium)
H+ (From soil)
NO3– (nitrate)
Nitrifying bacteria
Denitrifying bacteria
Root
NH4+
Nitrate and nitrogenous organic compounds exported in xylem to shoot system
Ammonifying bacteria

26. 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)

27. Root Nodules
Along a legumes roots are swellings called nodules composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria
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
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.
Nodules
Roots

28. Development of a soybean root nodule
Infection thread
Rhizobium bacteria
Dividing cells in 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.
Developing root nodule
Dividing cells in pericycle
Infected root hair 1 2 3
Nodule vascular tissue 4
3 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
The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant.

29. Symbiotic Nitrogen Fixation and Agriculture
The agriculture benefits of symbiotic nitrogen fixation are the basis for 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

30. 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
Agricultural importance: Farmers and foresters often inoculate seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae

31. Ectomycorrhizae
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
Endodermis
Fungal hyphae between cortical cells
(colorized SEM)
100 m
(a)

32. Endomycorrhizae
In endomycorrhizae the microscopic fungal hyphae extend into the root
Epidermis
Cortex
Fungal hyphae
Root hair
10 m
(LM, stained specimen)
Cortical cells
Endodermis
Vesicle
Casparian strip
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)

33. Epiphytes, Parasitic Plants, and Carnivorous Plants
Epiphytes use a host for support but do not extract nutrients from the host
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’ flytrap
Pitcher plants
Sundews
Dodder
Some plants have nutritional adaptations that use other organisms in nonmutualistic ways

34. Carnivorous plant movie

35. Improving the Protein Yield of Crops
Plant breeding research has resulted in new varieties of maize, wheat, and rice that are enriched in protein
Such research addresses the most widespread form of human malnutrition: protein deficiency
Many of the projects creating GMOs (genetically modified organisms) are aimed at protein enrichment of crops.
High lysine corn