Nutrition of Horticultural Crops Exam 3 (Phosphorus and Potassium)

Question 1

What is the most obvious difference between the global nitrogen and global phosphorus cycle?

Answer 1

there is no atmospheric reservoir for phosphorus like there is with nitrogen

Question 2

Phosphorus typically exists at LOW pH in the soil in what two immobile and insoluble complexes?

Answer 2

Fe–P & Al–P

Question 3

Phosphorus typically exists at HIGH pH in the soil in what kind of immobile and insoluble complex?

Answer 3

Ca–P

Question 4

What are the two processes which can liberate phosphorus from the insoluble/immobile complexes they form with cations for uptake by the plant?

Answer 4

desorption & weathering

Question 5

What is the action taken by microbes which liberate phosphorus from organic molecules called?

Answer 5

mineralization

Question 6

What term refers to the taking of plant-available phosphorus from the soil and sequestering it temporarily in organic molecules?(i.e., the opposite of mineralization)

Answer 6

immobilization

Question 7

What is a regrettable source of phosphorus contamination to aquatic reservoirs?

Answer 7

sewage entry

Question 8

Because phosphate is an anion (PO43-) which is repelled by the weakly electronegative plasma membrane, what is used to facilitate phosphate’s entry?

Answer 8

symport mechanism embedded in the membrane

Question 9

What does a symport mechanism make use of to drive phosphate entry?

Answer 9

hydrogen ion gradients on each side of the plasma membrane

Question 10

What are the enzymes which can assimilate inorganic phosphate into different organic molecules like carbohydrates and lipids?

Answer 10

phosphorylases

Question 11

To liberate inorganic phosphate from iron or aluminum complexes, what can plants secrete to alter the chemistry of the acidic rhizosphere?

Answer 11

low molecular weight organic acids (LMWOAs)

Question 12

What is an example of a low molecular weight organic acid exuded by plant roots?

Answer 12

malic acid

Question 13

The purpose of plants exuding malic acid is to make phosphorus more available in acid soils. How does it do this?

Answer 13

malic acid has a high affinity for aluminum, which causes it to bind to the metal in Al–P complexes, kicking off the phosphorus group

Question 14

How do phosphorylases and phosphotases differ from one another?

Answer 14

phosphotases break down organic phosphorus molecules into inorganic phosphorus, which is the OPPOSITE the opposite behavior demonstrated by phosphorylases

Question 15

Why are phosphatases more energetically costly for plants to produce than LMWOAs?

Answer 15

phosphatases are larger molecules

Question 16

Once inorganic phosphorus has been acted upon by phosphorylase within the cytoplasm and sequestered into an organic molecule, what is it referred to as (besides “organic phosphorus”)?

Answer 16

substrate phosphorus

Question 17

What are three kinds of biological molecules phosphorus may be found within?

Answer 17

(1) nucleic acids (DNA & RNA)
(2) membrane phospholipids
(3) adenosine triphosphate (ATP)

Question 18

What are two similar characteristics in a phosphorus deficiency and a nitrogen deficiency?

Answer 18

signs of stunted growth in the aerial tissues & promoted growth of the root system

Question 19

How do changes in foliage color differ between nitrogen-deficient and phosphorus-deficient plants?

Answer 19

nitrogen-deficient leaves typically become lighter and yellow, while phosphorus-deficient leaves can become darker and take on a blue/purple/reddish hue

Question 20

What is the reason for which phosphorus-deficient leaves appear darker and more blue/red?

Answer 20

relatively higher concentrations of anthocyanin pigments

Question 21

What is a model organism which, under phosphorus deficiency, ceases the growth of its roots at the apical meristem and switches over to growth from the lateral buds, resulting in a high number of cluser roots?

Answer 21

Arabidopsis thaliana

Question 22

What are three root exudates Arabidopsis thaliana has been shown to secrete larger volumes of when the concentration of phosphorus in the soil is only 0.3125 mM, as compared to when the soil concentration is 1.25 mM?

Answer 22

(1) glutamic acid
(2) malic acid
(3) nicotinic acid

Question 23

What are the root-endophytic fungi which one can find in about 80% of all terrestrial plant species?

Answer 23

mycorrhizae

Question 24

What are the two clades of fungi which contain the majority of mycorrhizal species?

Answer 24

Ascomycota (“sac fungi”) & Basidiomycota (“club fungi”)

Question 25

What is a fungus from the clade Ascomycota which is typically innocuous in the human gut microbiome but can become deleterious to health?

Answer 25

Candida albicans

Question 26

What is the common name for the disease “candidiasis”, which is associated with Candida albicans?

Answer 26

yeast infection
(if it is the oral infection, it can be known as “thrush”)

Question 27

What is the common name for a plant-pathogenic sac fungus which affects a valuable fruit crop?

Answer 27

apple scab (Venturia inaequalis)

Question 28

What is the common name for a plant-pathogenic sac fungus which affects a commodity crop?

Answer 28

wheat ergot (Claviceps purpurea)

Question 29

What are three genera of entomopathogenic fungi (EPF) which are ascomycotes?

Answer 29

(1) Beauveria
(2) Cordyceps
(3) Metarhizium

Question 30

What are the common names for three kinds of edible fungi which are from the clade Basidiomycota?

Answer 30

(1) chicken-of-the-woods (Laetiporus sulphureus)
(2) chanterelle mushroom (Cantharellus cibarius)
(3) common mushroom (Agaricus bisporus)

Question 31

What is the common name for a plant-pathogenic club fungus which affects a commodity crop?

Answer 31

corn smut (Ustilago maydis)

(known in Spanish as “huitlacoche”)

Question 32

What kind of mycorrhizae are generally observed in the roots of the acid-loving members of the Ericaceae, which includes cranberries and blueberries?

Answer 32

ericoid mycorrhizae (EMF)

Question 33

What kind of mycorrhizae form structures around the epidermal cells of the plant roots but do not enter the intercellular spaces?

Answer 33

ectomycorrhizae

Question 34

What is the most common kind of mycorrhizal fungus in plants?

Answer 34

arbuscular mycorrhizae (AMF)

Question 35

What is the species of fungus which demonstrates an ectomycorrhizal behavior when associating with Norway spruce (Picea abies), but presents as an ericoid mycorrhiza in association with the European blueberry (Vaccinium myrtillus)?

Answer 35

Acephala macrosclerotiorum

Question 36

What should mycorrhizal products like Pro-Mix BX never be combined with at the same time in the soil?

Answer 36

fungicides

Question 37

Only the (1)_________ of a mycorrhizal fungi can colonize (2)______________, meaning the symbiotes will only form associations during their (3)_______________ reproductive state.

Answer 37

(1) spores
(2) plant roots
(3) asexually

Question 38

How many sets of chromosomes do fungi usually have when they colonize plant roots?

Answer 38

one set of chromosomes (haploid)

Question 39

Generally speaking, conditions which reduce photosynthesis result in lower mycorrhizal establishment rates in plant roots. What are three conditions which result in reduced rates?

Answer 39

(1) cold soil temperatures
(2) flooded soils
(3) reduced soil moisture

Question 40

What are three molecules which can be called “potash” depending on the nation one is in?

Answer 40

(1) potassium chloride (KCl)
(2) potassium sulfate (K2SO4)
(3) potassium carbonate (K2CO3)

Question 41

What two countries together have more than 80% of the global reserves of potassium for agriculture?

Answer 41

(1) Canada ( ~46.1%)
(2) Russia ( ~34.5%)

(46.1% + 34.5% = 80.6%)

Question 42

About what percent of the global potassium reserves are found in the United States?

Answer 42

the United States has about 1.4% of the global potassium reserves (just behind Germany’s ~1.5%)

Question 43

Most of the potassium which goes into fertilizer is mined from underground reservoirs using what process?

Answer 43

water is pumped underground and later recovered with dissolved K+, after which the water is evaporated and the potassium salt is collected for potash production

Question 44

Just like with phosphorus, what group of exudates do plants exploit to take up potassium from the soil?

Answer 44

affinity transporters

(low affinity transporters used to acquire potassium when soil concentrations are high)

(high affinity transporters used to acquire potassium when soil concentrations are low)

Question 45

What role does potassium play in the nucleic acids DNA and RNA

Answer 45

potassium acts as a counter-ion and stabilizes their partial negative charges to prevent them from folding in on themselves

Question 46

What role does potassium play in the guard cells of leaves?

Answer 46

potassium maintains turgor pressure in the guard cell, causing them to become flaccid when they are no longer present

Question 47

Potassium deficiency symptoms are similar to those of a water deficiency. What are two such manifestations?

Answer 47

(1) plants are wilted due to flaccid guard cells and display downward-oriented petioles
(2) necrosis of the leaf margins may arise in very deficient plants