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Essential Elements

• Original research don by Julius von Sachs 1860 using hydroponics

– Using various solutions found ones that supported plant life –Sachs found several elements that were needed in relatively large amounts and called these major or macro essentialelements – those found to be needed in very small amounts were called minor, micro essential, or trace elements

– Criteria for Essentiality

• The element must be necessary for complete, normal plant development through the life cycle

• The element itself must be necessary, and no substitute can be effective

• The element must be acting within the plant not outside it

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Mineral Deficiency Diseases

• Causes of Deficiency Diseases

– Desert soils

• Osmotic drought• Some plants adapted to absorb both water and solutes – eventually

secretes minerals out via glands on leaves• Other plants precipitate excess salts as crystals

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Mineral Deficiency Diseases

– Serpentine Soils

• Those deficient in calcium

• If a plant is sensitive the these low amount it usually becomes diseased or is out competed by other plants

– Non-native Plants, Crops or Ornamentals

• Selected for high yields

• Require nitrogen and other mineral enrichment (fertilization)

• Harvesting crops – What effect does this have on soil nutrient content?

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Mineral Deficiency Diseases

• Symptoms of Deficiency Diseases –

– Irrespective of the element most plants demonstrate chlorosis (yellowing of the leaves, leaves become brittle and dry)

– Nitrogen and or phosphorous deficiency causes leaves to become brown or purplish with the accumulation of xanthocyanins

– Some leaves demonstrate necrosis, dead patches of cells

• Potassium deficiency leads to dead leaf tips and margins

• Manganese deficiency leaf tissue between veins dies

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Mineral Deficiency Diseases

• Mobile and Immobile Elements – problem seen in parts of plants of different ages – for some once deposited in plant tissue cannot move to other parts of the plant

– Immobile Elements – boron, calcium, iron

• Once picked up by plant are incorporated into plant tissues

• Plants parts being produced at the time utilize these elements

• Eventually elements are depleted from the soil

• Once elements are removed from the soil older parts of the planthave none to use

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Mineral Deficiency Diseases

– Mobile Elements – chlorine, magnesium, nitrogen, phosphorous, potassium, and sulfur

• Once depleted from soil older leaves give up their nutrients to younger leaves

• What is the adaptive significance of this?

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Soils and Mineral Availability

• Two important aspects of rock

– Cyrstalline in nature - if essential elements are part of the crystal structure then they are not available to the plant

– Water can be trapped in the crystal and made unavailable

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Soils and Mineral Availability

• Weathering of rock produces soil

– Physical Weathering

• Breakdown of rock via physical action

– Wind– Water movement– Temperature changes

• Produces soil particles of different sizes

– Coarse sand – 2 - .2 mm– Fine sand - .2 - .02 mm– Silt - .02 - .002 mm– Clay - <.002 mm, form micelles

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Soils and Mineral Availability• As seen earlier texture effects water and mineral holding capacity

– Sands very well aerated

– Water passes through them too easily giving it a poor field capacity

– Chemical Weathering

• Typically the result of acids produced via decay

– Organic acids

– Carbon dioxide

– Where warmth, moisture and large amounts of decaying matter weathering takes place very rapidly producing – releases bound nutrients

• Not only decreases particle size but also changes soil chemistry

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Soils and Mineral Availability» Positive ions are released leaving negatively charged soil particles behind

» In sands the surface area to volume ratio is small but in smaller particles this has a greater effect – positively charged ions can bind to the particles helping the soil retain these nutrients rather than having them be leached away

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Soils and Mineral Availability

• Cation Exchange

– Cations are bound to soil particles and must the removed for use

– Roots and root hairs via respiration produce carbon dioxide –Results in the production of what?

– Acids from other sources also aid cation exchange

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Soils and Mineral Availability

• Soil Acidity – important in

– Cation exchange

– Retention of cations in the soil

– Solubility of certain elements

• Acidic soils – following minerals are soluble, can reach toxic levels

– Aluminum– Manganese

• Alkaline soils – certain minerals become insoluble and unavailable

– Iron– Zinc

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Soils and Mineral Availability

– On average best pH between 6.5 – 7.0

– Certain plants have adapted to particular pH’s

• Endodermis and Selective Absorption of Substances

– Once again, substances can enter the cells of roots by passing through the cell membranes of the cells (selectivity of membraneplays a roll) and via the apoplast (no control)

– What is the control of substances entering the vascular tissues of roots for transport?

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Soils and Mineral Availability• The presence of the Casparian strip of the endodermis prevenst

free passage from the apoplast – substances must pass through the cell membranes that are highly selective

• Mycorrhizae and the Absorption of Phosphorous

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Nitrogen Metabolism

• Nitrogen for the most part exists as a gas, N2, and is fairly non-reactive – for organisms to use it it must be converted to an active form – three methods

– Nitrogen Fixation – conversion of nitrogen to nitrate, nitrite or ammonium

• Man can produce nitrate or ammonium from nitrogen industrially –expensive, energy intensive

• Natural methods

– Lightning

• Bacterial Fixation

– Enzyme nitrogenase converts N2 into NH3 (ammonia) once in the cell gains a proton and becomes ammonium NH4

+ - enzyme is very sensitive to, and reacts with oxygen making it ineffective

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Nitrogen Metabolism– Nitrogen Fixing microorganisms

» Free living in soil, contribute nitrogen to soil upon their death - Nostoc(cyanobacterium) other bacteria, Azobacter, Clostridium, Kelbsiell

» Symbiotic bacteria – best known Rhizobium – as mentioned earlier assists in pioneering plants

– Nitrogen Reduction – typically nitrogen is available to roots in the form of nitrate (the result of microorganisms oxidizing ammoniumfor energy) – as a result plants must reduce nitrate back to ammonium for their use – to do this they must

• Donate 8 electrons for each nitrogen atom – this requires a large amount of energy – two steps

– Step 1 -

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Nitrogen Metabolism– Step 2 – nitrite is reduced to ammonium

» Not well understood» Requires NADPH and NADH – can’t be used to make ATP

– Nitrogen Assimilation – using of ammonium to make organic molecules

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Storage of Minerals in Plants

• For the most part in plants minerals are stored in solution within the large central vacuole of plant cells

• Seeds differ in that they must be light weight, while still possessing the nutrients necessary to produce an entirely new plant

– Stores amino acids by crystallizing them into a structure calledthe protein body

• Protein body may also contains crystals of a substance called phytin, which stores cations such as Mg2+, Ca 2+, Zn2+ and K+, which it donates upon germination