This document discusses mineral nutrition and absorption in plants. It covers essential mineral nutrients, how they are absorbed by plant roots from the soil solution and transported throughout the plant. The key points are: 1) Plants require mineral nutrients which are absorbed from the soil by roots and transported via xylem to other plant parts. 2) There are 16 essential mineral nutrients grouped by their functions in plant metabolism and structure. 3) Nutrients are absorbed as ions by root hairs and transported through the root before loading into the xylem for long-distance transport. 4) Once in plant tissues, nutrients are assimilated into organic molecules to support plant growth and metabolism.

1. Mineral Nutrition and Absorption & Assimilation
Mineral Nutrition
“The study of how plants obtain and use mineral nutrients “
Plant mineral nutrition – essential elements required by plants
Mineral absorption and assimilation – Absorbed by roots primarily in
the form of inorganic ions from the soil, translocated into various plant
parts and incorporation into bio-molecules

2. Plant mineral nutrition - elemental nutrients (inorganic, simplest
chemical form) are required for metabolism, and growth and development
of plants
Essential elements – products of soil organic matter recycling and
weathering that are absorbed by roots from soil solution, uptake with water
These nutrients together with CO2 and H2O, and sunlight (light energy)
allow plants to synthesize all other necessary molecules, essentially
autotrophic (self-feeding)
Essential mineral nutrients often limit plant growth and development
reducing maximal biomass and crop production
Agricultural practice is to optimize plant nutrient status by soil amendment
with fertilizers

3. A nutrient is essential if:
It is a required component of structure (silicon in the cell wall) or plant
metabolism
OR
It is necessary for plant growth, development or reproduction, i.e. species
survival

4. ESSENTIAL NUTRIENTS
An essential element is
Without which a plant cannot complete its life cycle
Has a clear physiological role
If plants are provided with these essential elements and energy from sunlight,
they can synthesize all the compounds they need for normal growth.

6. Classification of essential mineral nutrients by function
Group 1 (N and S) – components of organic molecules
N – amino acids/proteins, nucleotides/nucleic acids
S – amino acid (cysteine), lipids, intermediary molecules (acetyl-
CoA)
Group 2 (P, Si, B) – P- energy storage (ATP) or Si & B - cell wall
structure

8. Group 3 (K, Ca, Mg, Cl, Mn, Na) – present as ions in cells, enzyme co-
factors, osmotic adjustment, signaling

9. Group 4 (Fe, Zn, Cu, Ni, Mo) – metals involved in redox reactions
(electron transfer)

10. Special Techniques Are Used in Nutritional Studies
Identification of essential elements was facilitated by the use of solution
culture systems or hydroponics
Some micronutrients are required in trace amounts, essentially was
difficult to establish because soils often contain sufficient amounts of
these trace elements
Solution culture requires a synthetic “medium” containing essential
nutrients, e.g. Hoagland’s solution

13. Mineral Deficiencies Disrupt Plant Metabolism and
Function
Inadequate supply of an essential element results in a nutritional disorder
manifested by characteristic deficiency symptoms.
In hydroponic culture, withholding of an essential element can be readily
correlated with a given set of symptoms for acute deficiencies
Nutrient deficiency symptoms in a plant are the expression of metabolic
disorders resulting from the insufficient supply of an essential element.
These disorders are related to the roles played by essential elements in
normal plant metabolism and function

14. Diagnosis of deficiency symptoms can be more complex, because:
Deficiencies of several elements may occur simultaneously.
Deficiencies or excessive amounts of one element may induce
deficiencies or excessive accumulations of another.
Some plant diseases may produce symptoms similar to those of
nutrient deficiencies.
Some essential element participates in many different metabolic
reactions and have multiple roles in plant metabolism.
Diagnosis

15. When relating acute deficiency symptoms to a particular essential
element, an important clue is the extent to which an element can be
recycled from older to younger leaves.
Some elements, such as nitrogen, phosphorus, and potassium, can
readily move from leaf to leaf; others, such as boron, iron, and calcium,
are relatively immobile in most plant species
If an essential element is mobile, deficiency symptoms tend to appear first
in older leaves.
Deficiency of an immobile essential element will become evident first in
younger leaves
Important Consideration

17. Nutrient deficiency symptoms – soils have a finite mineral nutrient
load capacity
Plant nutrient deficiency symptoms may be used to determine when
and what type of soil nutrient amendment (fertilization) is necessary
Symptoms are complex, occurring from deficiency of different
individual nutrients and further complicated by stresses, see Plant
Physiolgy by Taize & Ziger for an in-depth study of plant nutrient
deficiency symptoms

18. Nutrient deficiency symptoms – N, P, K, Ca
Epstein & Bloom Mineral Nutrition of Plants 2004

19. Cation exchange capacity (CEC) of soil particles facilitates nutrient
availability to plants - soil particles, both inorganic (gravel, >2 mm to clay
< 2 µm), and organic matter, have a negative charge, CEC
CEC facilitates availability of cations (positively charged elements or
molecules) for absorption by plant roots
5.5 The principle of cation exchange on the surface of a soil particle
CEC – cations form electrostatic interactions with soil particles, exchange
occurs during equilibrium, net exchange is concentration & charge strength
dependent

20. Negatively charged ions (anions), e.g., NO3
-
, H2PO4
-
, Cl-
- remain in the
soil solution between particle spaces, adhesion of water
Limited anion exchange capacity of soils - anions form bridges with
multivalent cations like Fe2+
or Al3+
,and H2PO2
-
OR, anions are present in relatively insoluble compounds e.g., SO4
2-
in
gypsum (CaSO4), which are gradually released
However, anions are repelled by surface particle charge and tend to be
leached through the soil to the ground water

21. pH and mineralization – affect mineral nutrient availability in soil solution,
pH 5.5 to 6.5 is optimal
Decomposition of organic material lowers the pH
Soil amendments alter pH - lime (CaO, CaCO3, Ca(OH)2, attract protons)
increases pH (alkaline)
Sulfur - reduces pH (mineralization results in release of sulfate and hydrogen
ions) of the soil solution
5.4 Influence of soil pH on the availability of nutrient elements in organic soils
Shaded area is the relative nutrient availability to plants

22. Nutrients move in the soil solution by pressure-driven bulk flow and
diffusion, directly linked to water movement

23. Root structure and mineral nutrient absorption – roots acquire water and
mineral nutrients
5.7 Taproot system of two adequately watered dicots: sugar beet (A), alfalfa (B)
Plants vary in root development based on adaptation to local soil conditions,
water and nutrients

24. Hydrotropism – roots have the capacity to sense water, higher
ψw
5.6 Fibrous root systems of wheat (a monocot)
Plants respond to water and nutrient deprivation by remodeling their root
architecture to maximize root surface area (secondary roots and root hairs)
and “seek” water and nutrients

25. + - portion of root system receiving complete nutrient solution
- - Part of the root system receiving the solution deficient
in specified nutrient

26. Mineral Absorption and
Assimilation
Main regions of a primary root
are the meristematic zone,
elongation and maturation zones
Meristematic – root cap protects
the root, gravitropic (gravity
response), quiescent zone of
meristem initials, progenitors of
other cells
Elongation zone (0.7 to 1.5 mm
from apex) – reduced cell
division, rapid cellular
elongation and development of
cell types, including endodermis
with Casparian strip, xylem and
phloem

27. Maturation zone – root hair zone
that increases the surface area for
absorption of water and mineral
nutrients

28. Mycorrhizal fungi facilitate water and mineral nutrient uptake into roots –
extend the root absorption surface area
Mycorrhiza fungi – symbiotic (sugar for mineral nutrients) association between a
fungus and plant roots, 83% of dicot species, 79% of monocots and all
gymnosperms
Ectomorphic mycorrhizal fungi – hyphae extend into the cortex (apoplast) of
plants and into the soil, up to 100% increase in surface area for nutrient
absorption, reduces the nutrient depletion zone at the root surface
5.10 Root infected with ectotrophic mycorrhizal fungi

29. Vesicular arbuscular mycorrhizal fungi – hyphae are less dense and penetrate
into cortical cell symplast where they branch (arbuscule) and transfer nutrients
to the plant root, hypae extend from the root facilitating nutrient acquisition
beyond the root surface
5.11 Association of vesicular–arbuscular mycorrhizal fungi with a section of a plant root
It is not known precisely how nutrients move from the hyphae to the plant
cells, i.e. diffusion or release at hyphal death

30. Mineral nutrient (ion) uptake into roots, xylem loading and movement
to shoots – absorption by roots, radial movement to the xylem, uptake to
shoots in the transpiration stream (movement of water)
Movement of ions through the soil is due primarily to pressure- driven bulk
flow, with water
Ion uptake from soil into roots occurs predominantly in the maturation/root hair
zone (extension of the epidermis) of primary and secondary roots
1.1 Schematic representation of the body of a typical dicot (Part 1)

31. Radial transport and xylem loading – through the apoplast or symplast of
the root hair, epidermis and cortex with water
At the endodermis, ions must enter the symplast of endodermal cells
because the suberized Casparian strip restricts apoplast movement
Uptake in the root cell symplast is by diffusion based on the electrochemical
potential
4.4 Pathways for water uptake by the root

32. Xylem loading – movement from the endodermis to the tracheary elements
(tracheids or vessel elements
Xylem parenchyma cells - directly connected to the endodermis and
tracheary elements (tracheids or vessel elements) and regulate ion
movement into the xylem
Transport proteins regulate ion transport into and out of the xylem
6.20 Tissue organization in roots (Part 2)
Ion movement from root to shoot is
primarily in the transpiration
stream, pressure-driven bulk flow

33. Mineral nutrient assimilation – incorporation of mineral nutrients into
organic molecules
Assimilation - requires substantial energy, e.g. 25% of the plant energy
budget is consumed for N assimilation
Assimilated mineral nutrients - N either NH4
+
or NO3
-
, SO4
2-
, and H2
PO4
2-

34. Nitrogen – biogeochemical cycling of nitrogen
12.1 Nitrogen cycles through the atmosphere
N2
(N N) - 78% of the atmospheric volume≡
N2
– fixed biologically or by the Haber-Bosch process into NH4
+
, oxidized to
NO3
-

35. N2
(N N) fixation symbiosis - primarily legumes by bacterial symbionts≡
(Rhizobia) into ammonium (NH3
) (nitrogenase), which at physiological pH
is converted to NH4
+
Otherwise, nitrogen absorbed into roots as NO3
-
(NO3
-
−H+
symporter) or
NH4
+
(uniporter)
NO3
-
is reduced to NH4
+
(nitrate and nitrite reductases w/ferrodoxin as the
electron donor)
NH4
+
is assimilated into glutamine and then glutamate (glutamine
synthase, glutamate synthase), sometimes ureides (legumes), 12 ATP/N
assimilated is required

36. Sulfur – SO4
2-
is a product of soil weathering
SO4
2-
is absorbed by roots (SO4
2-
- H+
symporter) and translocated
APS is then reduced to produce SO3
2-
(APS reductase), SO3
2-
is reduced to
sulfide (S2-
, sulfite reductase, ferrodixin), which condenses with O-acetylserine
(OAS) (S2-
+ OAS cysteine) to form cysteine (then methionine)→
12.15 Structure and pathways of compounds involved in sulfur assimilation
Assimilation occurs primarily in
leaves, photosynthesis produces
reduced ferrodoxin and
photorespiration generates serine,
14 ATP consumed per S assimilated
SO4
2-
is assimilated into 5’-adenylsulfate/adenosine-5’-phosphosulfate (SO4
2-
+
ATP APS + PPi), reaction catalyzed by ATP sulfurylase→

37. Phosphorous – HPO4
2-
, uptake (PO4
2-
-H+
symporter) and translocated form
Assimilated into ATP (ATP synthase), photosynthesis, oxidative phosphorylation
(respiration)
Cation mineral nutrients (K, Ca, Mg, Fe, Mn Cu, Co, Na, Zn) – function as ions or
exist in complexes with organic molecules via noncovalent bonds, metals
facilitate redox reactions
Coordination bonds (several oxygen or nitrogen atoms share electrons) to form
a bond with a cation nutrient, chlorophyll a

38. Electrostatic interactions – charge group attraction, e.g., Ca2+
for
carboxylate groups in pectin (Ca2+
-pectate)