Chapter 37 Plant Nutrition. Concept 37.1: Plants require certain chemical elements to complete their life cycle Plants derive most of their organic mass.

Chapter 37

Plant Nutrition

• 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

Figure 37.2

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

• Essential elements in plants

Table 37.1

• 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

• The most common deficiencies– Are those of nitrogen, potassium, and

phosphorus

Figure 37.4

Phosphate-deficient

Healthy

Potassium-deficient

Nitrogen-deficient

• Concept 37.2: 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

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

particles

Figure 37.6b

(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–

–– –

– – –––

• 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

Figure 37.9

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)

NH4+

(ammonium)

H+

(From soil)

NO3–

(nitrate)Nitrifyingbacteria

Denitrifyingbacteria

Root

NH4+

Soil

Atmosphere

Nitrate and nitrogenous

organiccompoundsexported in

xylem toshoot system

Ammonifyingbacteria

• 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– 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

Figure 37.10a

(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

• Inside the nodule– Rhizobium bacteria assume a form called

bacteroids, which are contained within vesicles formed by the root cell

Figure 37.10b

(b) Bacteroids in a soybean root nodule. In this TEM, a cell froma root nodule of soybean is filledwith bacteroids in vesicles. The cells on the left are uninfected.

5 m

Bacteroidswithinvesicle

• 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

Figure 37.11

Infectionthread

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.

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

• Exploring unusual nutritional adaptations in plants

Figure 37.13

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