Lecture 8: Acquiring phosphorus Flashcards
Proteoid roots known as
Cluster roots
Proteoid roots also known as
cluster roots
is phosphate renewable?
NO.
its essential but a non-renewable resource
Is phosphorous inorganic or organic?
-Phosphorus is an essential inorganic nutrient
what % of P applied as fertiliser is bound to
80-90%
to soil particles and is highly immobile. Mass flow typically delivers as little as 1–5 % of plant P demand.
what % of P applied as fertilisers to soil is bound and highly immobile
80-90% Mass flow typically delivers as little as 1-5% of plant P demand
How can P supply be improved?
Root interception of Pi can be increased by root proliferation (cluster or proteoid roots) (the exceptions)
and mycorrhizal symbioses (the rule)
species with proteiod roots can grow in
solid with poorly available nutrients; most do not form mycorrhizal symbioses
cluster roots has a increased/decreased root surface area
massive increase in root surface area (up to 25-fold)
Cluster (proteoid) roots exude compounds facilitating the:
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
exudative burst refers to
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.
exudation of cluster roots requires how much input of carbon from the shoot
MASSIVE
50-100% when active, 10-30% over a season
is phosphate renewable resource?
No. is essential but will run out eventually
phosphorous is an essential organic/inorganic nutrient?
inorganic
after N whats the most important inorganic nutrient for plants
P
nucleic acids, metabolites, phospholipids etc
what % of P applied as fertiliser is bound to
80-90%
to soil particles and is highly immobile. Mass flow typically delivers as little as 1–5 % of plant P demand.
How can P supply be improved?
Root interception of Pi can be increased by root proliferation (cluster or proteoid roots) (the exceptions)
and mycorrhizal symbioses (the rule)
species with proteiod roots can grow in
soils with poorly available nutrients; most do not form mycorrhizal symbioses
Cluster (proteoid) rots provide affect on root surface area
MASSIVE INCREASE
up too 25-fold
cluster roots exude compounds facilitating the
mobilisation of nutrients from the soil
In cluster roots what are the organic anions role
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
in proteoid roots whats the ‘exudative burst’
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.
Proteoid roots: exudation requires
massive input of carbon from the shoot (50-100% when active, 10-30% over a season)
Hakea victoria & Banksia speciosa (western australia)
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.
high phosphorous-use efficiency in Proteaceae, replacement of phospholipids with
non-phospholipids (galactolipids and sulpholipids), without compromising photosynthesis
high phosphorous-use efficiency in Proteaceae: low ribosome abundance increases P-use efficiency because:
- 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.
Mycorrhizas are
highly evolved, symbiotic associations between soil fungi and plants roots
mycorrhizas is between
fungi (Basidiomycetes, Ascomycetes and Zygomycetes) and >90% vascular plants
Mycorrhiza alters quantity of carbon allocated below ground example Pinus ponderosa by
more carbon below ground, more translocate to below-ground. less in needles
non-mycorrhizal plants are most common in
disturbed habitats, or sites with extreme environmental soil conditions
2 ways mycorrhizal plants increase plant nutrient supply:
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
1) by extending the VOLUME of soil accessible to plants (cf. cluster roots) HOW???
fingal hyphae can respond to localised sources of soil nutrients more rapidly than roots
2) by acquiring NUTRIENT FORMS that would not normally be available to plants HOW???
- 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
Growth is promoted by mycorrhiza when
less phosphate is available
VAM =
vesicular-arbuscular mycorrhizas
VAM are
most common non-pathogenic symbioses in the roots of plants
-fungi are obligately symbiotic (bistrophic) Zygomycetes
% of plant families have AM
> 95%
evidence of AM in
earliest land plants (400mya)
-probably not very host specific
in VAM fungal hyphae form
tree‐like branched structures (arbuscules) and vesicles (V) within the cell that act as the functional interface for nutrient exchange.
ectormycorrhizas associated with
with basidiomycetes or ascomycetes
ectomycorrhizas specific?>
not very specific
trees with ectomycorrhizas are dominant in
coniferous forests, especially in cold boreal or alpine regions
ectomycorrhizas are common on trees and shrubs in
-many broad‐leaved forests in temperate or Mediterranean regions
• also in some tropical or subtropical savannah or rain forest habitats
orchid mycorrhizas:
- 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)
