Nutrient uptake Flashcards
Nutrient movement to the root
- diffusion
- mass flow
- root interception
Diffusion
is most important for N(NO3^-), P, K
Mass flow
is most important for Ca, Mg, S, micronutrients
root interception
is not important
Minerals taken up by plant roots are in a_________
watery solution
Water and minerals are absorbed through the ______ of the root and must be taken up by _______ before they enter the _______
epidermis
root cells
xylem
What controls what minerals enter the xylem
-selective permeability of the plasma membrane of root cells
What are the two pathways by which water and minerals enter the xylem
- Intracellular route
- extracellular route
Intracellular route
-water and solutes are selectively taken up by a root epidermis cell, usually a root hair, and transported from cell to cell through plasmodesmata
Extracellular route
water and solutes pass into the root in the porous cell walls of root cells; they do not enter any cell plasma membrane until they reach the root endodermis
The cells of the endodermis contain a waxy barrier called the ________
Casparian strip
Casparian strip
-regulates uptake of minerals that enter the root via the extracellular route (stopped by the strip)
- Water and solutes that have entered the root without crossing a cell plasma membrane are blocked
- specialized cells of the endodermis take up water and minerals selectively
Soil particles and plant roots participate in ________
cation exchange
Cation exchange
the transfer of positive ions such as Ca, Mg, K from soil to plant roots
soil particles tend to _____ cations can make uptake by plants ______
bond
difficult
______ are readily taken up by plants and not affected as much by soil
Anions
How does a plant get nutrients
- mineral movement to root by diffusion or bulk or root growth
- uptake controlled at root endodermis
- uptake by either simple diffusion (no protein), facilitated diffusion (protein channel), or active uptake (requires energy and a protein carrier)
simple diffusion
no protein
facilitated diffusion
protein channel
active up take
requires energy and a protein carrier, proton pump
Active diffusion
active uptake
Passive diffusion
- simple diffusion
- facilitated diffusion
_______ is main way plants can increase nutrient uptake
root elongation
root elongation
- increased root:shoot ratio
- increased investment in roots
- root proliferation in nutrient hot spots
- root growth occurs where it does the most good
-longer root hairs
_______ increase soil volume sued by plants
mycorrhizae
mycorrhizae
- trade carbohydrates for nutrients (balanced parasitism)
- most advantageous for immobile nutrients (e.g., phosphate)
Mechanisms of nutrient uptake
- Active transport most important (requires energy, moves against concentration gradient
- Abundant nutrients may enter by diffusion or mass flow
cation
an ion that carries a positive charge
anion
an ion that carries a negative charge
cation exchange
a process-cations in solution exchanged with cations on exchange sites if minerals and OM
Cation exchange capacity (CEC):
the total amount of exchangeable cations that a particular material or soil can adsorb at a given pH
Strength of adsorption
related to hydrated ionic radius and valence
-the smaller the radius and greater the the valance, the more closely and strongly the ion is adsorbed
strength=valance/radius
Controls on ion exchange
- strength of adsorption
- Relative concentration in soil solution
- Valance
valance
the combing power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with
Cation exchange capacity
- the sum total of all exchangeable cations that a soil can adsorb
- expressed in terms of positive charge adsorbed per unit mass
if CEC = 10 cmol/kg
soil adsorbs 10 cmol of H^+, can exchange it with 10 cmol K^+, or 5 cmol Ca^2+
number of charges, not number of ions is what matters
mole
the mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of C 12
1 centimole= 10^2 moles
exchange affinity is referred to as the ______
Lyotropic series
Lyotropic series
H^+ > Al^3+ > Ca^2+ > Mg^ 2+ > NH4^+ > K^+ > Na^+
Held more strongly Held more weakly
strength of adsorption proportional to valance/ hydrated radius
CEC Depends on
- amount of clay and organic matter
- type of clay minerals present
The interchange between a cation in solution and one on a colloid must be _____ balanced
charge
CEC
-OM has highest CEC
-Clay has high but not all clays created equal
-As increase sand content decrease CEC
-sands don’t adsorbed cations, if do really weak
-
Rule of thumb for estimation of a soil’s CEC
CEC= (% OM100)+ (%clay50)
but the CEC of clay minerals ranges from 3 to 150.
CEC capacity
Soil humus:150-200 cmol/kg
Clay: 3-150
Silt loams, sandy loams, loamy sands: less than 25
