Chapter 4: Mineral Nutrition Flashcards
what are mineral nutrients? Why do plants need them?
elements such as nitrogen, phosphorus, and potassium in the form of inorganic ions
- composition an physiological processes
biosphere
the parts of the surface and atmosphere of earth that support life as well as the organisms living there
mineral nutrition
the study of how plants obtain and use mineral nutrients
Over half the energy used in agriculture is expended on the production, distribution, and application of nitrogen fertilizers
what happens to fertilizers when applied to crop plants?
Crop plants typically use less than half of the fertilizer applied to the soils around them
The remaining materials leach into surface water or groundwater and contribute to air pollution and climate change
Many water wells now exceed nitrate concentrations
atmospheric nitrogen deficiencies
enhanced nitrogen availability released into the environment from human activities and deposited in the soil by rainwater
essential element
one that is an intrinsic component in the structure of metabolism of a plant or whose absence causes severe abnormalities in plant growth, development, or reproduction and may prevent a plant from completing its life cycle
- Essential elements function in plant structure, metabolism, and cellular osmoregulation
- concentrations are dependent on species, tissues, and growing conditions
why aren’t hydrogen, carbon, and oxygen not considered mineral nutrients?
because they are obtained from water or CO2
macronutrients
nitrogen, potassium, calcium, magnesium, phosphorous, sulfur, and silicon
micronutrients
chlorine, iron, boron, manganese, sodium, zinc, copper, nickel, and molybdenum
group 1 of essential elements
Nitrogen and sulfur constitute the first group of essential elements. Plants assimilate these nutrients via biochemical reactions involving oxidation and reduction to form covalent bonds with carbon and create organic compounds (e.g., amino acids, nucleic acids, and proteins).
group 2 of essential elements
The second group is important in energy storage reactions or in maintaining structural integrity. Elements in this group are often present with the elemental group is covalently bound to an organic molecule
- phosphorous, silicon, boron
group 3 of essential elements
The third group is present in plant tissue as either free ions dissolved in the plant water or ions electrostatically bound to substances such as the pectic acids present in the plant cell wall. Elements in this group have important roles as enzyme cofactors, in regulating osmotic potentials, and in controlling membrane permeability.
- potassium, calcium, magnesium, chlorine, zinc, sodium
group 4 of essential elements
The fourth group, comprising metals such as iron, has important roles in reactions involving electron transfer.
- iron, manganese, copper, nickel, molybdenum
what is the purpose of a nutrient solution?
A solution containing only inorganic salts that supports the growth of plants in sunlight without soil or organic matter.
This technique is called a solution culture or hydroponics - A technique for growing plants with their roots immersed in nutrient solution without soil. Also called hydroponics.
Used in the production of greenhouse and indoor crops like tomato, cucumber, and hemp
aeroponics
plants are grown with their roots suspended in air while being sprayed continuously with a nutrient solution
Easy manipulation of gaseous environment
ebb-and-flow system
the nutrient solution periodically rises to immerse plant roots and then recedes, exposing the roots to a moist atmosphere
what is a modified Hoagland solution?
contains all known mineral elements needed for rapid plant growth. The concentrations of these elements are set at the highest possible concentrations without pro ducing toxicity symptoms or salinity stress, and thus may be several orders of magnitude higher than those found in the soil around plant roots
Grow in the medium without having to replenish it but can injure young plants although some researchers will replenish frequently at less concentrations to avoid this
Has both nitrate and ammonium which helps the plant grow better
what is a major problem with nutrient solutions?
A major problem with nutrient solutions is maintaining the availability of iron
Iron can precipitate out
Chelators are added to form soluble complexes with cations so then it is available to plants
A carbon compound (e.g., malic acid or citric acid) that can form a soluble non covalent complex with certain cations, thereby facilitating their uptake.
why is diagnosing deficiencies in essential elements complicated?
Deficiencies of several elements may occur simultaneously in different plant tissues.
Deficiencies or excessive amounts of one element may induce deficiencies or excessive accumulations of another element.
Some virus-induced plant diseases may produce syn1pton1s similar to those of nutrient deficiencies.
what general statements about deficiencies can be made?
Deficiency symptoms tend to appear first in older leaves
Deficiency of immorbile essential elements become evident first in younger leaves
mobile elements
nitrogen, potassium, magnesium, phosphorous, chlorine, sodium, zinc, and molybdenum
immobile elements
calcium, sulfur, iron, boron, and copper
soil analysis
the chemical determination of the nutrient continent in a soil sample from the root zone
Reflects the potentially available nutrients to plant roots
Does not tell how much a plant needs to absorb
plant tissue analysis
In the context of mineral nutrition, the analysis of the concentrations of mineral nutrients in a plant sample
tissue concentration of a nutrient depends on the balance between nutrient absorption and dilution of the amount of nutrient through growth.
What are the three zones in response to increasing tissue concentrations of a nutrient?
deficiency, adequate, and toxic
deficiency zone
In plant tissue, the range of concentrations of a mineral nutrient below the critical concentration, the highest concentration were reduced plant growth or yield is observed
When the nutrient concentration in a tissue sample is low, growth is reduced
Nutrient availability is directly related to growth or yield
adequate zone
As nutrient availability and absorption continue to increase, a point is reached at which further addition of the nutrient is no longer related to increases in growth or yield, but is reflected only in increased tissue concentrations.
critical concentration
In plant tissue, the minimum concentration of a mineral nutrient that is correlated with maximum growth or yield.
Between the deficiency and adequate zones
toxic zone
In plant tissue, the range of concentrations of a mineral nutrient in excess of the adequate zone and where growth or yield declines.
what are inorganic particles in the solid phase?
potassium, phosphorus, calcium, magnesium, and iron
what does soil pH affect?
nutrient availability, soil microbes, and root growth
at what pH is root growth facored?
between 5.5-6.5
what affects the soil pH?
Acidity weathers rocks that have potassium, magnesium, calcium, and manganese
And increases the solubility of carbohydrates, sulfates, and phosphates
Soil pH is lowered by organic matter, ammonium assimilation, and rainfall
what happens if soil is saline?
May inhibit plant growth that exceeds water availability
Sodium chloride and sulfate are the most common in soil
rhizosphere
the immediate microenvironment surrounding the root
If poor in nutrients or too dry, roots grow slow
If improved, roots grow quicker
describe monocot roots
Root development starts with 3-6 primary root axes from a seed
They then grows adventitious roots called nodal roots
Both grow to form the fibrous root system
describe eudicot roots
Develop root systems with a main single root axis called a taproot
Lateral roots develop and form a branch root system
what does the development of root systems in monocots and eudicots depend on?
Development of the root system in both monocots and eudicots depends on the activity of the root apical meristem and the production of lateral roots
- roots can grow more than 50 meters deep
What are the three zones of root activity?
meristematic, elongation, and maturation zones
meristematic zone
cells divide both in the direction of the root base to form cells that will differentiate into the tissues of the functional root and in the direction of the root apex to form the root cap
- very tip beneath the root cap
- root hairs appear in the maturation zone
root cap
protects the delicate meristematic cells as the root expands
Secretes mucigel to protect from desiccation and transfer nutrients to the root
elongation zone
the region of rapid and extensive root cell elongation showing few, if any cell divisions
Cells elongate rapidly and undergo a final round of decisions to produce a central ring of cells called the endodermis and is thickened by the casparian strip
Endodermis divides the root into the cortex (outside) and stele (inside)
cortex
Ground tissue in the region of the primary stem or root located between the vascular tissue and the epidermis, mainly consisting of parenchyma.
stele
In the root, the tissues are located interior to the endodermis. The stele contains the vascular elements of the root: the phloem and the xylem.
why does the phloem develop more rapidly than the xylem?
Phloem develops more rapidly than the xylem because its function is critical at the root apex
Carbohydrates have to flow through it to support cell division
maturation zone
The region of the root where differentiation occurs, including the production of root hairs and functional vascular tissue.
how are nutrients moved in the soil?
bulk flow or diffusion
bulk flow: nutrients are carried by water moving through the soil toward the root - used when nutrient concentrations are high
diffusion: move from a region of higher concentration to lower concentrations of nutrients at the root surface
nutrient depletion zone
when diffusion is too slow to maintain high nutrient concentrations near the root surface
Mycorrhiza
The symbiotic (mutualistic) association of certain fungi and plant roots. Facilitates the uptake of mineral nutrients by roots. Plant gives the fungi carbohydrates and receives nutrients from fungi and increases surface area
what percentage of terrestrial plants form mycorrhizal associations? what percentage are arbuscular?
90% / 80%
What can stop mycorrhizal formation?
Flooding, plowing, high concentrations of fertilizer, soil fumigation
what are the characteristics of arbuscular mycorrhizae?
- hyphae enter the cell wall (though they do not penetrate the membrane or enter the protoplast)
what are the characteristics of ectomycorhizzae?
- exists between the cell walls and form a sheath around the entire root
- can also exist independently and produce toadstools, puffballs, and truffles around tree stumps
when are nutrients most accessible to plants?
- at near neutral pH
- nutrients are inaccessible at very high or very low pH
- acid souls have low N availability
- basic soils may reduce P availability
how much can a rye plant grow after 16 weeks?
more than 500 km of total root length
