Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?

Figure 37.2 The uptake of nutrients by a plant: a review

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

Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?2. Why do plants need K+?

- Macronutrients – needed in large amounts (9)- Micronutrients – needed in small amounts (8)

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Table 37.1 Essential Elements in Plants

Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?2. Why do plants need K+?3. What makes up soil?

- Weathered rock- Topsoil – mixture of weathered rock, living organisms, & humus- Humus – remains of partially decayed organic matter- Loams – most fertile soils made of equal amounts of clay, silt & sand

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Figure 37.5 Soil horizons

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

Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?2. Why do plants need K+?3. What makes up soil?4. How do minerals become available to plant roots?

- Cation exchange

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Figure 37.6 The availability of soil water and minerals

Soil particle surrounded byfilm of water

Root hair

Water available to plant

Air space

H2O + CO2 H2CO3 HCO3– +

Root hair

Soil particle

K+

Cu2+Ca2+

Mg2+K+

K+

H+

H+

–

–– –

– – –––

(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.

(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 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.

Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?2. Why do plants need K+?3. What makes up soil?4. How do minerals become available to plant roots?5. How is soil conservation achieved?

- Fertilizers- N-P-K- Organic

- Irrigation - problems- Erosion prevention

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Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?2. Why do plants need K+?3. What makes up soil?4. How do minerals become available to plant roots?5. How is soil conservation achieved?6. How do plants obtain nitrogen?

- nitrogen-fixing bacteria

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Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants

Atmosphere

N2

Soil

N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)

NH4 + (ammonium)

H+

(from soil)

Soil

Atmosphere

Ammonifyingbacteria

Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)

NH4 + (ammonium)

H+

(from soil)

NO3 – (nitrate)Nitrifying

bacteria

Denitrifyingbacteria

Soil

Atmosphere

Ammonifyingbacteria

Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants

Atmosphere

N2

Soil

N2 N2

Nitrogen-fixingbacteria

Organicmaterial (humus)

NH3

(ammonia)

NH4 + (ammonium)

H+

(from soil)

NO3 – (nitrate)Nitrifying

bacteria

Denitrifyingbacteria

Root

NH4 +

Soil

AtmosphereNitrate and nitrogenous

organiccompoundsexported in

xylem toshoot system

Ammonifyingbacteria

AssimilationLegumes have root nodules with symbiotic bacteriaRhizobium

Figure 37.10 Root nodules on legumes

(a) 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.

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

5 m

Bacteroidswithinvesicle

Nodules

Roots

Chapter 37: Plant Nutrition1. What are the nutritional requirements of plants?2. Why do plants need K+?3. What makes up soil?4. How do minerals become available to plant roots?5. How is soil conservation achieved?6. How do plants obtain nitrogen?7. What are some nutritional adaptations that aid plants?

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Figure 37.13 Unusual Nutritional Adaptations in Plants

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

37.13 Sun Dew Trap Prey