Lecture 8: Acquiring phosphorus

Question 1

Proteoid roots known as

Answer 1

Cluster roots

Question 2

Proteoid roots also known as

Answer 2

cluster roots

Question 3

is phosphate renewable?

Answer 3

NO.

its essential but a non-renewable resource

Question 4

Is phosphorous inorganic or organic?

Answer 4

-Phosphorus is an essential inorganic nutrient

Question 5

what % of P applied as fertiliser is bound to

Answer 5

80-90%

to soil particles and is highly immobile. Mass flow typically delivers as little as 1–5 % of plant P demand.

Question 6

what % of P applied as fertilisers to soil is bound and highly immobile

Answer 6

80-90% Mass flow typically delivers as little as 1-5% of plant P demand

Question 7

How can P supply be improved?

Answer 7

Root interception of Pi can be increased by root proliferation (cluster or proteoid roots) (the exceptions)
and mycorrhizal symbioses (the rule)

Question 8

species with proteiod roots can grow in

Answer 8

solid with poorly available nutrients; most do not form mycorrhizal symbioses

Question 9

cluster roots has a increased/decreased root surface area

Answer 9

massive increase in root surface area (up to 25-fold)

Question 10

Cluster (proteoid) roots exude compounds facilitating the:

Answer 10

mobilisation of nutrients from soil. Organic anions, especially citrate, mobilise P by chelating soil minerals such as Fe, Al, Ca which bind P. Acid phosphotases hydrolyse organic forms of P

Question 11

exudative burst refers to

Answer 11

the rootlets exude little or no material until fully grown, but then, over a few days, exude large amounts of citrate and malate. Then exudation drops back to almost zero. May prevent soil bacteria from depleting the exudates.

Question 12

exudation of cluster roots requires how much input of carbon from the shoot

Answer 12

MASSIVE

50-100% when active, 10-30% over a season

Question 13

is phosphate renewable resource?

Answer 13

No. is essential but will run out eventually

Question 14

phosphorous is an essential organic/inorganic nutrient?

Answer 14

inorganic

Question 15

after N whats the most important inorganic nutrient for plants

Answer 15

P

nucleic acids, metabolites, phospholipids etc

Question 16

what % of P applied as fertiliser is bound to

Answer 16

80-90%

to soil particles and is highly immobile. Mass flow typically delivers as little as 1–5 % of plant P demand.

Question 17

How can P supply be improved?

Answer 17

Root interception of Pi can be increased by root proliferation (cluster or proteoid roots) (the exceptions)
and mycorrhizal symbioses (the rule)

Question 18

species with proteiod roots can grow in

Answer 18

soils with poorly available nutrients; most do not form mycorrhizal symbioses

Question 19

Cluster (proteoid) rots provide affect on root surface area

Answer 19

MASSIVE INCREASE

up too 25-fold

Question 20

cluster roots exude compounds facilitating the

Answer 20

mobilisation of nutrients from the soil

Question 21

In cluster roots what are the organic anions role

Answer 21

Organic anions, especially citrate, mobilize P by chelating soil minerals such as Fe, Al, and Ca, which bind P. Acid phosphatases hydrolyze organic forms of P

Question 22

in proteoid roots whats the ‘exudative burst’

Answer 22

the rootlets exude little or no material until fully grown, but then, over a few days, exude large amounts of citrate and malate. Then exudation drops back to almost zero. May prevent soil bacteria from depleting the exudates.

Question 23

Proteoid roots: exudation requires

Answer 23

massive input of carbon from the shoot (50-100% when active, 10-30% over a season)

Question 24

Hakea victoria & Banksia speciosa (western australia)

Answer 24

Proteaceae in south‐western Australia occur on severely P‐impoverished soils. They have very low leaf P concentrations, but relatively fast rates of photosynthesis, suggesting they do not compromise their metabolic machinery in order to save P.

Question 25

high phosphorous-use efficiency in Proteaceae, replacement of phospholipids with

Answer 25

non-phospholipids (galactolipids and sulpholipids), without compromising photosynthesis

Question 26

high phosphorous-use efficiency in Proteaceae: low ribosome abundance increases P-use efficiency because:

Answer 26

• fewer ribosomes means the demand for P is decreased.
• young leaves delay formation of the photosynthetic machinery (low plastidic ribosome abundance).
• spreading investment of P in ribosomes over time allows sequential use of rRNA for the synthesis of proteins required for new cells and structural defence (sclerenchyma) then chloroplast maturation.

Question 27

Mycorrhizas are

Answer 27

highly evolved, symbiotic associations between soil fungi and plants roots

Question 28

mycorrhizas is between

Answer 28

fungi (Basidiomycetes, Ascomycetes and Zygomycetes) and >90% vascular plants

Question 29

Mycorrhiza alters quantity of carbon allocated below ground example Pinus ponderosa by

Answer 29

more carbon below ground, more translocate to below-ground. less in needles

Question 30

non-mycorrhizal plants are most common in

Answer 30

disturbed habitats, or sites with extreme environmental soil conditions

Question 31

2 ways mycorrhizal plants increase plant nutrient supply:

Answer 31

1) by extending the VOLUME of soil accessible to plants (cf. cluster roots)
2) by acquiring NUTRIENT FORMS that would not normally be available to plants

Question 32

1) by extending the VOLUME of soil accessible to plants (cf. cluster roots) HOW???

Answer 32

fingal hyphae can respond to localised sources of soil nutrients more rapidly than roots

Question 33

2) by acquiring NUTRIENT FORMS that would not normally be available to plants HOW???

Answer 33

• associations ahem a greater benefit when P is present in less-soluble forms
• hyphae can utilise both inorganic and simple organic sources of N and P

Question 34

Growth is promoted by mycorrhiza when

Answer 34

less phosphate is available

Question 35

VAM =

Answer 35

vesicular-arbuscular mycorrhizas

Question 36

VAM are

Answer 36

most common non-pathogenic symbioses in the roots of plants

-fungi are obligately symbiotic (bistrophic) Zygomycetes

Question 37

% of plant families have AM

Answer 37

> 95%

Question 38

evidence of AM in

Answer 38

earliest land plants (400mya)

-probably not very host specific

Question 39

in VAM fungal hyphae form

Answer 39

tree‐like branched structures (arbuscules) and vesicles (V) within the cell that act as the functional interface for nutrient exchange.

Question 40

ectormycorrhizas associated with

Answer 40

with basidiomycetes or ascomycetes

Question 41

ectomycorrhizas specific?>

Answer 41

not very specific

Question 42

trees with ectomycorrhizas are dominant in

Answer 42

coniferous forests, especially in cold boreal or alpine regions

Question 43

ectomycorrhizas are common on trees and shrubs in

Answer 43

-many broad‐leaved forests in temperate or Mediterranean regions
• also in some tropical or subtropical savannah or rain forest habitats

Question 44

orchid mycorrhizas:

Answer 44

• largest plant family; small seeds for dispersal
• coils of hyphae within roots or stems
• young orchid seedlings are entirely dependant on mycorrhizal fungi for their nutrition (C + nutrients)