Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter14: Soils and Mineral Nutrition - Coggle Diagram
Chapter14: Soils and Mineral Nutrition
definitions
hydroponic solution-a water solution that contains all essential elements and in which plants can be cultivated. Hydroponic solutions are used to examine the effects of various chemicals on plant growth, and also to cultivate plants without soil.
mineral nutrition-covers a variety of types of plant metabolism.
essential elements discovered by Sachs are called the major or macro essential elements because they are needed in large quantities by plants
With such improved chemicals, it was soon discovered that there exists a group of minor or micro essential elements, also called trace elements. Iron, Boron, Chlorine, Copper, Manganese, Molybdenum, and Zinc.
hydroponic solution
formalized and used extensively by Julius von Sachs in 1860
a solution is developed that supports plant growth
other chemicals needed by plants are toxic if present at too high a concentration
the form in which a chemical is present makes a difference: Nitrogen is important, but in addition to nitrate and ammonia, which plants use, other nitrogen compounds are added to the same solution, unsuspected reactions may occur that create toxic compounds or convert useful
Causes of Deficiency Diseases
all types of soil contain at least small amounts of all essential elements; under natural conditions it is rare to encounter plants whose growth and development are seriously disrupted by a scarcity or an excess of mineral elements.
certain types of excess minerals, if absorbed, can be precipitated in vacuoles as crystals; although a cell may contain large amounts of the mineral, only on metabolism.
consequently many cells throughout the plant use oxalic acid to precipitate the excess calcium as crystals of calcium oxalate. This is costly because each oxalate ion in the crystal could have instead been used in the tricarboxylic acid (TCA) cycle to generate adenosine triphosphate (ATP).
Symptoms of Deficiency Diseases
chlorosis-leaves lack chlorophyll, tends to be yellowish, and are often brittle and papery. deficiencies of either nitrogen or phosphorus cause another common symptom, the accumulation of anthocyanin pigments
necrosis-the death of patches of tissue (necrosis can also be caused by bacterial, viral, and fungal infections.) the location of the necrotic spots depend on the particular element: potassium deficiency causes leaf tips and margins to die, whereas manganese deficiency causes the leaf tissues between veins to die even though all of the veins themselves remain alive and green.
Mobile and Immobile Elements
an important diagnostic aspect is whether symptoms appear in young leaves or older leaves. this is related to the mobility of the essential element. Boron, Calcium, and Iron are immobile elements.
the elements Chlorine, Magnesium, Nitrogen, Phosphorus, Potassium, and Sulfur are mobile elements; even after they have been incorporated into a tissue they can be translocated to younger tissue.
Soils and Mineral Availability
soils are derived from rock by processes of weathering. the initial rock may be volcanic (Granite or Basalt), metamorphosed (Marble or Slate), sedimentary (Sandstone or Limestone), or other types but two things are important; rock has a crystalline structure and trapped within the structure are numerous types of contaminating ions and elements.
two fundamental processes of weathering convert rock to soil; physical weathering and chemical weathering. as its name implies, physical weathering is the breakdown of rock by physical forces such as wind, water movement, and temperature changes.
runoff from rainstorms, avalanches, and similar forces wash rock fragments and pebbles into streams and rivers, where physical weathering accelerates.
physical weathering produces a variety of sizes of soil particles; the largest ones that are technically important to soil are grains of coarse sand, with a size range of 2.0-0.2 mm. particles only one tenth this large (0.2-0.02 mm) are fine sand, and those one tenth of the (0.02-0.002mm) are silt.
the finest particles, smaller than 0.002 mm in diameter, are clay particles, technically known as micelles.
Cation Exchange
cations must first be freely dissolved in soil solution; this is done by cation exchange.
roots and root hairs respire, giving off CO2. as this dissolves in the soil solution, some reacts chemically with water, forming carbonic acid, H2CO3.
Soil Acidity
soil pH is important for cation exchange and the retention of cations in the soil during heavy rain.
many factors affect soil acidity, such as the chemical nature of the original rock, but probably the most important factor is rainfall.
Mycorrhizae and the Absorption of Phosphorus
the roots of 90% of all species of plants form a symbiotic association with soil fungi, and this relationship is called a mycorrhiza; the symbiosis permits plants to absorb phosphorus efficiently.
this mycorrhizal symbiosis is essential to most plants; plants in sterilized soil grow poorly and show signs of phosphorus deficiency even if the soil contains adequate amounts of phosphorus.
Nitrogen Fixation
nitrogen fixation is the conversion of N2 gas into nitrate, nitrite, of ammonium. all forms of nitrogen that are substrates for a variety of enzymes.
natural processes fix over 190 million tons of nitrogen annually. lighting is important; the energy of a lightning strike passing through air converts elemental nitrogen to a useful form that dissolves in rain and falls to the earth.
these organisms have nitrogenase, an enzyme that uses N2 as a substrate. it forces electrons and protons onto nitrogen, reducing it from the +0 to the -3 oxidation state.
Nitrogen Reduction
nitrogen reduction is the process of reducing nitrogen in the nitrate ion, NO3-, from an oxidation sate of +5 to the -3 oxidation state of ammonium, which is also the oxidation state of nitrogen in amino acids, nucleic acids and many other biological compounds.
