Chapter 37

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 37Chapter 37

Plant Nutrition


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 root and shoot systems of a vascular plant ensure extensive networking with both reservoirs of inorganic nutrients



Concept 37.1: 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

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Minerals

H2O

H2O

O2

O2

CO2

CO2


Macronutrients and Micronutrients

• More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants

• A chemical element is considered essential if it is required for a plant to complete its life cycle

• Researchers use hydroponic culture to determine which chemicals elements are essential

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Control: Solutioncontaining all minerals

Experimental: Solutionwithout potassium



• Nine of the essential elements are called macronutrients because plants require them in relatively large amounts

• The remaining eight are called micronutrients because plants need them in very small amounts


Symptoms of Mineral Deficiency

• Symptoms of mineral deficiency depend on the nutrient’s function and mobility 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

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Healthy

Phosphate-deficient

Potassium-deficient

Nitrogen-deficient


Concept 37.2: Soil quality is a major determinant of plant distribution and growth

• Along with climate, soil texture and composition are major factors determining whether a plant can grow well in a certain location

• Texture is the soil’s general structure

• Composition is the soil’s organic and inorganic chemical components


Texture and Composition of Soils

• Topsoil is a mixture of particles of rock, living organisms, and humus (the remains of partially decayed 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

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A

B

C


• After a heavy rainfall, water drains from the larger spaces of soil, but smaller spaces retain water because of its attraction to clay and other particles

• The film of loosely bound water is usually available to plants

Animation: How Plants Obtain Minerals from Soil

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Soil particle surrounded byfilm of water

Root hair

Wateravailableto plant

Root hair

Air space

Cation exchange in soil

Soil water

Soil particle


• Acids derived from roots contribute to a plant’s uptake of minerals when H+ displaces mineral cations from clay particles


Soil Conservation and Sustainable Agriculture

• In contrast with natural ecosystems, agriculture depletes the mineral content of soil, taxes water reserves, and encourages erosion

• The goal of soil conservation strategies is to minimize this damage


Fertilizers

• Commercial fertilizers contain minerals that are mined or prepared by industrial processes

• Organic fertilizers are composed of manure, fishmeal, or compost


• Agricultural researchers are developing ways to maintain crop yields while reducing fertilizer use

• Genetically engineered “smart” plants inform the grower when a nutrient deficiency is imminent

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No phosphorusdeficiency

Beginningphosphorusdeficiency

Well-developedphosphorusdeficiency


Irrigation

• Irrigation is a huge drain on water resources when used for farming in arid regions

• It can change the chemical makeup of soil


Erosion

• Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States

• Precautions, such as contour tillage, can prevent loss of topsoil



• The goal of soil management is sustainable agriculture, a commitment embracing a variety of farming methods that are conservation-minded


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 reclaims contaminated areas


Concept 37.3: 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


Improving the Protein Yield of Crops

• Agriculture research in plant breeding 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


Concept 37.4: Plant nutritional adaptations often involve relationships with other organisms

• Two types of relationships plants have with other organisms are mutualistic:

– Symbiotic nitrogen fixation, involving roots and bacteria

– Mycorrhizae, involving roots and fungi


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

• For agriculture, the key symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)


• Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria

LE 37-10LE 37-10

Bacteroidswithinvesicle

Nodules

Roots

Pea plant root. Bacteroids in a soybeanroot nodule.

5 µm


• Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell


• The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen

• Each legume species is associated with a particular strain of Rhizobium

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Infectedroot hair

Infectionthread

Rhizobiumbacteria

Bacteroid

Dividing cellsin root cortex

Bacteroid

Developingroot nodule

Dividing cells inpericycle

NodulevasculartissueBacteroid


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

• Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation

• A non-legume such as maize is planted one year, and the next year a legume is planted to restore the concentration of nitrogen in the soil


Mycorrhizae and Plant Nutrition

• Mycorrhizae are mutualistic associations of fungi and roots

• The fungus benefits from a steady supply of sugar from the host plant

• The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption


The Two Main Types of Mycorrhizae

• In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root

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Epidermis

Mantle(fungal sheath)

Fungalhyphaebetweencorticalcells

Endodermis

Mantle(fungalsheath)

Cortex

Ectomycorrhizae.

100 µm

(colorized SEM)


• In endomycorrhizae, microscopic fungal hyphae extend into the root

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Epidermis

Fungalhyphae

Cortex

Endomycorrhizae.

Roothair

Endodermis

Vesicle

Casparianstrip

Arbuscules

Cortical cells10 µm

(LM, stained specimen)


Agricultural Importance of Mycorrhizae

• Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae


Epiphytes, Parasitic Plants, and Carnivorous Plants

• Some plants have nutritional adaptations that use other organisms in nonmutualistic ways

Video: Sun Dew Trapping Prey

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Staghorn fern, and epiphyte. This tropical fern (genus Platycerium) grows on large rocks, cliffs, and trees. It has two types of fronds: branched fronds resembling antlers and circular fronds that form a collar around the base of the fern.

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Mistletoe, a photosynthetic parasite. Dodder, a nonphotosynthetic

parasite.Indian pipe, a nonphotosynthetic parasite.

Dodder

Host’s phloem

Haustoria

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Venus’ flytrap.

Pitcher plants. Sundews.

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