Mineral Nutrition

Nutrients1. Definition2. Categories3. Essential versus Non-Essential4. Evidence

Fig 37.2

Julius Sachs 1860’s

Mineral Nutrition - Overview1. Some minerals can be used as is:

e.g. K+ ions for guard cell regulation

2. Some minerals have to be incorporated into other compounds to be useful:

e.g. Fe+ in the cytochrome complex of the light reactions

3. Some mineral compounds have to be altered to be useful:

NO3- must be converted to NH4

+ inside the plant

Chemical composition of plants

1. 80–85 % of an herbaceous plant is water.

2. Water is a nutrient since it supplies most of the hydrogen and some oxygen incorporated into organic compounds by photosynthesis.

3. But > 90% of the water absorbed is lost by transpiration.

4. Water’s primary function is to serve as a solvent.

5. Water also is involved in cell elongation and turgor pressure regulation

1. 95% “organic” – C, H, O from air & water, assimilated by photosynthesis

2. 5% inorganic minerals

Chemical composition of plants: dry weight

1. Nutrients that are required for a plant to grow from a seed and complete its life cycle.

2. 2 types: macronutrients & micronutrients

Essential Nutrients

1. Elements required by plants in relatively large amounts.

Macronutrients

CHOPKNS Ca Mg

Macro-nutrient

Form available to plants

Major functions

Carbon CO2 Organic compounds

Hydrogen H20 Organic compounds

Oxygen CO2 (air), O2 (soil)

Organic compounds

Phosphorus H2PO4-, HPO4

2- Nucleic acids, phospholipids, ATP

Potassium K+ Water balance (stomata), protein synthesis

Nitrogen NH4+, NO3

- Proteins, nucleic acids, hormones, chlorophyll

Sulfur SO42- Proteins

Calcium Ca2+ Cell walls & membranes, enzyme activation

Magnesium Mg2+ Chlorophyll, enzyme activation

Micronutrients

1. These elements are required by plants in relatively small amounts (<0.1% dry mass).

2. Major functions:

A. cofactors of enzymatic reactions

B. Light reactions of photosynthesis

C. Optimal concentrations highly species specific

Fe, B, Cl, Mo, Cu, Mn, Ni, & Zn

Table 37.1

dependent on:

1. the role of the nutrient in the plant

2. its mobility

Mineral Deficiencies

Immobile Nutrients

1. Once they have been incorporated into plant tissue, they remain (can’t return to phloem).

2. Boron, calcium, and iron

3. Growth = normal until the mineral is depleted from soil; new growth suffers deficiency and thus youngest tissues show symptoms first.

Mobile Nutrients

1. can be translocated by phloem to younger (actively growing) tissue.

2. Cl, Mg, N, P, K, and S

3. When mineral is depleted, nutrients translocated to younger tissue.

4. Thus older tissues show deficiency & then die

What is the adaptive value of nutrient mobility?

Mineral Deficiency1. Not common in natural populations. Why?

A. Plants have adapted to soil components2. Common in crops & ornamentals. Why?A. Human selection for biggest, fastest plants.

Need more nutrients than the soil providesB. Crop growth depletes the soil because no organic

matter return3. Deficiencies of N, P, and K are the most

common.4. Shortages of micronutrients are less common and

often soil type specific.5. Overdoses of some micronutrients can be toxic.

Mineral Deficiency Symptoms

1. Chlorosis – leaves lack chlorophyll: yellow, brittle, papery. Typically lack of N or Fe.

2. Necrosis – the death of patches of tissue

3. Purpling – deficiency of N or P, causes accumulation of purple pigments

4. Stunting – lack of water, N

Fig 37.4

Soils

Soil Formation

1. Forces

2. Horizons

3. Orders

4. Locations

Soils

1. What do soils give to plants??

A. minerals

B. nitrogen–fixing bacteria

C. mycorrhizal fungi

D. water

E. oxygen

Soil properties influence mineral nutrition1. Chemistry – determines which minerals are present

and available, thus affecting plant community composition

2. Physical nature – affects porosity, texture, density of soil, which affects #1

3. Soil organisms – A. decomposition & mineral returnB. Interact with roots to make nutrients availableC. Nitrogen! The only mineral that the plant can

ONLY get from reactions mediated by soil organisms.

Large, spaces for water & air

Small, more SA for retaining water & minerals

Soil texture & composition

1. Soil is created by weathering of solid rock by: water freeze/thaw, leaching of acids from organic matter, carbonic acid from respiration + water.

2. Topsoil is a mixture of weathered rock particles & humus (decayed organic matter).

3. Texture: sand, silt, clay

More about topsoil…..1. Bacteria, fungi, insects, protists, nematodes,

& Earthworms! Create channels for air& water, secrete mucus that binds soil particles

2. Humus: reservoir of nutrients from decaying plant & animal material

3. Bacterial metabolism recycles nutrients

Availability of soil nutrients1. Cations in soil water adhere to clay particles

(negatively charged surface)

2. Anions do not bind; thus they can leach! (NO3, HPO4, SO4)

3. Cations become available for root uptake by cation exchange – H+ displaces cations on the soil particle surface

4. H+ from carbonic acid – formed from water + CO2 released from root respiration

5. Humus – negatively charged & holds water & nutrients. Thus very important in the soil!!!!!

Thus soil pH is important!

1. Low pH = high H+ concentrationA. More cations released

B. Too much acid – cations leach…..mineral deficiency

2. High pHA. Not enough H+ for cation release….mineral

deficiency

Fig 37.6

Soil conservation1. Natural systems: decay recycles nutrients2. Agricultural systems: crops harvested, depleting

soil of nutrients & water3. Thus irrigation & fertilizer4. Fertilizers: N:P:K

A. Synthetic: plant-available, inorganic ions. Faster acting.a. Problem: b. leaching, acidifying the soil

B. Organic: slow release by cation exchange, holds water, thus less leaching

1. Use of plants to extract toxic metals from soil

2. Benefits: easier to harvest the plants than to remove topsoil!

Phytoremediation

NITROGEN

Why nitrogen?

1. Air is 80% Nitrogen, but…..

2. Macronutrient that is most often limiting. Why?Is almost always taken up as anions (NO3

-)

3. What’s it used for?Proteins (AAs), nucleic acids, chlorophyll production

The Nitrogen Cycle

Organic NNH4

NO3Decomposit

ion

N2

Ammonification Nitrification

Immobilization

Uptake

Leaching

Denitrification

N2 fixation

Nitrogen Metabolism in Plants

1. Steps:A. N fixation – conversion of N2 to NH3

B. Ammonification – conversion of NH3 or organic N into NH4

+

C. Nitrification – conversion of NH4+ to NO3

-

D. N reduction – conversion of NO3- back to

NH4+ within plant.

E. N assimilation – incorporation of NH4+ into

AAs, nucleic acids of the plant

But N is also lost….

1. Leaching – loss of NO3- by soil water

movement

2. Denitrification – conversion of NO3- back

to N2

Fig 37.9

All steps within the soil are mediated by bacteria!!!!

A. Nitrogen FixationThis process is catalyzed by the enzyme

nitrogenase, requires energy (ATP), and occurs in three ways:

a. Lightening – converts N in air to inorganic N that falls in raindrops

b. Non-symbiotic – certain soil bacteria

c. Symbiotic

c. Symbiotic Nitrogen Fixation

* Legumes: peas, beans, alfalfa

*The legume/bacteria interaction results in the formation of nodules on roots

*Plant – gets ample inorganic N source

*Bacteria – gets ample carbon source

Fig 37.10

d. Fixation in Nonlegumes

* Here in the NW: alder

* Azolla (a fern) contains a symbiotic N fixing cyanobacteria useful in rice paddies.

* Plants with symbiotic N fixers tend to be first colonizers. Why?

a. Unfortunately NH4+ is a highly desirable resource

for free–living bacteria, oxidizing it to NO3-.

b. Consequently the predominant form of N available to roots is NO3

-.

C. Nitrification

A. NO3- must be reduced back to NH4

+ in order to be incorporated into organics.

B. This process is energetically expensive but required.

D. Nitrate Reduction

a. The actual incorporation of NH4+ into organic

molecules in the plant body.

b. Process similar to that of an electron transport chain:

c. Reduced N passes through a series of carriers that function repeatedly but in the long run are unchanged.

d. Usually in roots

E. Nitrogen Assimilation

Nutritional Adaptations of Plants

1. Parasitic Plants

2. Carnivorous plants

3. Mycorrhizal relationships

1. Parasitic plants

A. Extract nutrients from other plantsa. Ex. Mistletoes on Douglas Fir & Ponderosa pine

b. Ex. Indian pipe – parasite on trees via mycorrhizae

Fig 37.15

http://www.nofc.forestry.ca/publications/leaflets/mistletoe_e.html

http://cals.arizona.edu/pubs/diseases/az1309/

2. Carnivorous plants

A. Digest animals & insects – why?

a. Grow in soils lacking an essential nutrient

B. Motor cells!

C. Trap insects & secrete digestive juices

Ex. Venus flytrap, pitcher plant, Darlingtonia

Figure 37.16

3. Mycorrhizal relationshipsA. Fungus & plant rootsB. Fungus gets carbosC. Plants get greater SA for water & phosphorus

uptakeD. Almost all plant species!E. 2 types:

a. Ectomycorrhizae – hyphae form dense sheath over root; extend into cortex & out into soil. Thickened roots of woody plants

b. Endomycorrhize – microscopic, more common.

Fig 37.12

Learning power will supplant physical power.