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 essential elements 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 1
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 2
Serpentine Soils Mineral Deficiency Diseases 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? 3
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 4
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 plant have none to use 5
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? 6
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 7
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 8
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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 10
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 11
Cation Exchange Soils and Mineral Availability 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 12
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 13
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 membrane plays a roll) and via the apoplast (no control) What is the control of substances entering the vascular tissues of roots for transport? 14
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 15
Nitrogen Metabolism Nitrogen for the most part exists as a gas, N 2, and is fairly nonreactive 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 N 2 into NH 3 (ammonia) once in the cell gains a proton and becomes ammonium NH 4 + - enzyme is very sensitive to, and reacts with oxygen making it ineffective 16
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 ammonium for 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 1-17
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 18
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 called the protein body Protein body may also contains crystals of a substance called phytin, which stores cations such as Mg 2+, Ca 2+, Zn 2+ and K +, which it donates upon germination 19