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Ch14: Soils and Mineral Nutrition, Figure1 - Coggle Diagram
Ch14: Soils and Mineral Nutrition
Essential elements
criteria for essentiality
the element must be necessary for complete, normal plant development through a full life cycle.
if an element is required any aspect of the plants growth, differentiation, reproduction, or survival, that element is essential
the element itself must be necessary and no substitute will work
the element must be acting within the plant, not outside of it
the essential elements discovered by Sachs are called the major/macro essential elements: they are needed in large quantities in plants
Macronutrients
Carbon, oxygen, hydrogen, nitrogen, potassium, calcium, phosphorus, magnesium, sulfur.
Micronutrients
Iron, chlorine, copper, manganese, zinc, molybdenum, boron
micro essential elements/micronutrients/trace elements: plants require these elements in low concentrations
Mineral Deficiency diseases
causes of deficiency diseases
most commonly encountered in nonnative crop species and ornamentals
does not seem common in natural populations
symptoms of deficiency diseases
chlorosis: leaves lack chlorophyll, tend to turn yellowish and be brittle and papery
deficiencies of either nitrogen or phosphorous cause the leaves to turn either a dark purple or blue
necrosis: the death of patches of tissue
potassium deficiency causes leaf tips and margins to die
manganese deficiency causes the leaf tissue between the veins to die
mobile and immobile elements
boron, calcium, and iron are immobile elements, they've been incorporated into plant tissue and remain in place
chlorine, magnesium, nitrogen, phosphorus, potassium, and sulfur are mobile elements, can be translocated into younger tissue
Soils and Mineral Availability
cation exchange
cations must be freely dissolved into soil solution through cation exchange before roots can absorb them
then that is broken down into a proton and a bicarbonate ion---> second proton and a carbonate ion
roots and root hairs respire giving off CO2, as this dissolves in the soil solution, some chemically reacts with water, forming H2CO3.
the presence of the protons positive charge disrupts the electrical attraction of the cation, liberating it and trapping the proton
the loss of this proton does not hurt the plant
soil acidity
soil pH, the concentration of free protons in the soil solution, is important for cation exchange
as the acidity increases (pH decreases), more cations are released from the soil micelles
these can be absorbed by roots or carried off by water
soil pH affects the chemical form of certain elements, causing them to change solubility
high rainfall leads to an abundance of vegetation that produces acids by means of respiration, decay, and excretion
low rainfall causes cations to build up, increasing soil alkilinity
the endodermis and selective absorption of substances
mycorrhizae and the absorption of phosphorus
the roots of 90% of all species of plants form a symbiotic relationship with soil fungi
this relationship is called a mycorrhiza
allows plants to absorb phosphorus productively
soils are derived from rock through weathering
physical weathering: wind, water movement, temp changes
chemical weathering: involves chemical reactions
Nitrogen metabolism
nitrogen reduction
the process of reducing nitrogen in the nitrate ion NO3- from an oxidative state of +5 to the -3 oxidative state of ammonium. This is also the oxidative state of nitrogen in amino acids, nucleic acids, etc
reducing nitrate back to ammonium requires 8 electrons for each nitrogen atom and a great deal of energy
as organic matter decays in the soil ammonium is released and becomes available
ammonium doesn't last long in soil, highly sought after by soil microbes
step 1: 2 electrons are added, reducing nitrogen from +5 to +3 and forming nitrite NO2-. The enzyme is nitrate reductase, carries electrons with a molybdenum ion
then nitrite is reduced to ammonium
nitrogen fixation
conversion of N2 gas into nitrate, nitrite, or ammonium, all forms of nitrogen that are substrates for various enzymes
natural processes fix over 190 million tons of nitrogen annually
bacteria and cyanobacteria: annually convert over 130 million tons of nitrogen to forms that plants and animals can use
these organisms posses nitrogenase, an enzyme that uses N2 as a substrate
some nitrogen fixing microorganisms are free-living in soil
some live symbiotically, living in tissues of host ferns and seed plants
nitrogen assimilation
the actual incorporation of ammonium into organic molecules in the plant body
process is similar to that of an electron transport chain
acceptor molecule is glutamate
glutamine and adp are formed
the transfer of an amino group from one molecule to another is transamination
other aspects of prokaryotes and nitrogen
nitrifying bacteria: bacteria that oxidize ammonium to nitrite, others oxidize nitrite to nitrate
this entire process is called nitrifiation
both types of these nitrifying bacteria are so common in soil that nitrite never builds up in the soil
whereas certain bacteria reduce and fix nitrogen, others oxidize it, which adversely affects plants
denitrification: process in which certain bacteria reduce nitrate to gaseous nitrogen, N2
obtaining nitrogen from animals
many bog-adapted plants obtain nitrogen through catching animals (carnivorous plants)
these plants obtain their energy through photosynthesis, not from the fats, carbs, etc of the animals they consume
storage of minerals within plants
storage mechanisms are necessary
animals tend to have large reservoirs of at least some elements
apparently, all parts of a plant except for seeds store minerals in soluble form in the central vacuoles of cells
consists of 1: nitrogen fixation, 2: nitrogen reduction, and 3: nitrogen assimilation
