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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Roots and rhizosphere / Rhizosphere phosphorus mobilization: phosphatases, organic acids and fast re-sorption

Rhizosphere phosphorus mobilization: phosphatases, organic acids and fast re-sorption

How roots and microbes free phosphorus that is bound in organic molecules and sorbed to iron and aluminium oxides. Low phosphate triggers phosphatases and organic acid release; released phosphate is re-sorbed within hours unless taken up, and rising supply switches the response off.

Boundary: where this process starts

Starts with: Soil solution Phosphate seldom exceeds about 10 uM (often 1-2 uM), so roots deplete a zone around themselves

Boundary: where it ends

Ends after: Roots take up Phosphate by high-affinity PHT1 transporters, directly or through mycorrhizal hyphae; Microbial biomass holds a few percent of total soil P but turns over fast, so microbes immobilize and release a large P flux

PARTICIPANTSRESOURCESPlant rootsRhizospheremicrobesIron oxidesMicrobesSoil solutionOtherparticipantsPhosphateIron oxidesPhosphorusOrganicphosphorusOrganic acidsImpact -3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Low Pi induces phosphatasesImpact +3 of 5. Click for details and evidence.Low Pi induces organic acid Impact +2 of 5. Click for details and evidence.Low P selects solubilizers nImpact -2 of 5. Click for details and evidence.Sorbed phytate resists hydroImpact +2 of 5. Click for details and evidence.Enzymes meet organic P poolsImpact +3 of 5. Click for details and evidence.Hydrolysis releases phosphatImpact +3 of 5. Click for details and evidence.Ligand exchange releases phoImpact +2 of 5. Click for details and evidence.Gluconic acid dissolves phosImpact +4 of 5. Click for details and evidence.Uptake competes with sorptioImpact -3 of 5. Click for details and evidence.Microbes immobilize part of Impact +3 of 5. Click for details and evidence.Better P status signals suffImpact -4 of 5. Click for details and evidence.↻ balances · strong · 0.5 Sufficiency represImpact +4 of 5. Click for details and evidence.Phosphorus supplied to plantImpact 02 of 5. Click for details and evidence.Microbial P pool turns overSoil solution Phosphate seldom exceeds about 10 uM (often 1-2 uM), so roots deplete a zone around themselves: uses up Phosphateuses upLow Phosphate induces plant and microbial phosphatases and phytases that hydrolyse organic P (about 30-65% of total soil P in many soils): uses PhosphateLow Phosphate induces plant and microbial phosphatases and phytases that hydrolyse organic P (about 30-65% of total soil P in many soils): uses PhosphorusLow Phosphate induces plant and microbial phosphatases and phytases that hydrolyse organic P (about 30-65% of total soil P in many soils): uses up Organic phosphorususes upPhytate (inositol hexakisphosphate) is the main identified organic P but sorbs strongly to Fe and Al oxides and clay, limiting access: uses Iron oxidesPhytate (inositol hexakisphosphate) is the main identified organic P but sorbs strongly to Fe and Al oxides and clay, limiting access: uses Organic phosphorusRoots and microbes exude citrate, malate and oxalate and extrude H+ to desorb phosphate from Fe and Al oxides and dissolve Ca phosphates: makes PhosphatemakesRoots and microbes exude citrate, malate and oxalate and extrude H+ to desorb phosphate from Fe and Al oxides and dissolve Ca phosphates: uses Iron oxidesRoots and microbes exude citrate, malate and oxalate and extrude H+ to desorb phosphate from Fe and Al oxides and dissolve Ca phosphates: makes Organic acidsmakesPhosphate-solubilizing bacteria (Pseudomonas, Bacillus) form gluconic acid via PQQ-glucose dehydrogenase; field inoculation responses are inconsistent: uses PhosphatePhosphate-solubilizing bacteria (Pseudomonas, Bacillus) form gluconic acid via PQQ-glucose dehydrogenase; field inoculation responses are inconsistent: makes Organic acidsmakesReleased phosphate is re-adsorbed to Fe and Al oxides within minutes to hours, so uptake must compete with fast sorption: uses up Phosphateuses upReleased phosphate is re-adsorbed to Fe and Al oxides within minutes to hours, so uptake must compete with fast sorption: uses Iron oxidesMicrobial biomass holds a few percent of total soil P but turns over fast, so microbes immobilize and release a large P flux: uses PhosphorusRoots take up Phosphate by high-affinity PHT1 transporters, directly or through mycorrhizal hyphae: uses up Phosphateuses upRising phosphate supply represses starvation responses, lowering phosphatase and organic acid release: uses Phosphatedepleted in root zonesPhosphate: depleted in root zonesinduces phosphataseproductionPhosphate: induces phosphatase productionhydrolysed byphosphatasesPhosphorus: hydrolysed by phosphataseshydrolysed to inorganicphosphateOrganic phosphorus: hydrolysed to inorganic phosphatebind phytate, limitingaccessIron oxides: bind phytate, limiting accesssorbs strongly to oxidesOrganic phosphorus: sorbs strongly to oxidesdesorbed and madeavailablePhosphate: desorbed and made availablerelease phosphate fromsurfacesIron oxides: release phosphate from surfacesexuded to desorbphosphateOrganic acids: exuded to desorb phosphatesolubilised for uptakePhosphate: solubilised for uptakeformed by bacterialglucose oxidationOrganic acids: formed by bacterial glucose oxidationre-adsorbed withinminutesPhosphate: re-adsorbed within minutesadsorb releasedphosphate quicklyIron oxides: adsorb released phosphate quicklyimmobilised and releasedquicklyPhosphorus: immobilised and released quicklytaken up by PHT1transportersPhosphate: taken up by PHT1 transportersrepresses starvationresponsesPhosphate: represses starvation responsesStart: Rhizospherephosphorusmobilizatio…STARTStart: Rhizosphere phosphorus mobilization: phosphatases, organic acids and fast re-sorptionEnd: Rhizospherephosphorusmobilizatio…ENDEnd: Rhizosphere phosphorus mobilization: phosphatases, organic acids and fast re-sorptionSoil solution Phosphateseldom exceeds about 10uM (often 1-2 uM), …📄1Soil solution Phosphate seldom exceeds about 10 uM (often 1-2 uM), so roots deplete a zone around themselvesLow Phosphate inducesplant and microbialphosphatases a…👍1📄1Low Phosphate induces plant and microbial phosphatases and phytases that hydrolyse organic P (about 30-65% of total soil P in many soils)Phytate (inositolhexakisphosphate) isthe main identifi…👍1📄1Phytate (inositol hexakisphosphate) is the main identified organic P but sorbs strongly to Fe and Al oxides and clay, limiting accessRoots and microbesexude citrate, malateand oxalate and extru…📄1Roots and microbes exude citrate, malate and oxalate and extrude H+ to desorb phosphate from Fe and Al oxides and dissolve Ca phosphatesPhosphate-solubilizingbacteria (Pseudomonas,Bacillus) form glucon…📄1Phosphate-solubilizing bacteria (Pseudomonas, Bacillus) form gluconic acid via PQQ-glucose dehydrogenase; field inoculation responses are inconsistentReleased phosphate isre-adsorbed to Fe andAl oxides with…📄1Released phosphate is re-adsorbed to Fe and Al oxides within minutes to hours, so uptake must compete with fast sorptionMicrobial biomass holdsa few percent of totalsoil P but turns ov…📄1Microbial biomass holds a few percent of total soil P but turns over fast, so microbes immobilize and release a large P fluxRoots take up Phosphateby high-affinity PHT1transporters, direct…📄1Roots take up Phosphate by high-affinity PHT1 transporters, directly or through mycorrhizal hyphaeRising phosphate supplyrepresses starvationresponses, loweri…📄1Rising phosphate supply represses starvation responses, lowering phosphatase and organic acid release
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
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Size of impact
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Soil solution Phosphate seldom exceeds about 10 uM (often 1-2 uM), so roots deplete a zone around themselves
Plant rootsSoil solutionPhosphate
Evidence (1) · added by Ember
  • Raghothama 1999, Annual Review of Plant Physiology and Plant Molecular Biology 50:665, Phosphate acquisition: Free inorganic phosphate in soil solution is typically below 10 uM and diffuses slowly. (confidence 0.8)
Low Phosphate induces plant and microbial phosphatases and phytases that hydrolyse organic P (about 30-65% of total soil P in many soils)
Plant rootsBacteriaFungiPhosphorusPhosphateOrganic phosphorus
Evidence (1) · added by Ember
  • Richardson & Simpson 2011, Plant Physiology 156:989: Organic P is often 30-65% of total soil P and requires phosphatase or phytase to become available. (confidence 0.7)
Phytate (inositol hexakisphosphate) is the main identified organic P but sorbs strongly to Fe and Al oxides and clay, limiting access
PhytateIron oxidesClay mineralsOrganic phosphorusIron oxides
Evidence (1) · added by Ember
  • Turner, Papházy, Haygarth & McKelvie 2002, Philosophical Transactions of the Royal Society B 357:449, Inositol phosphates in the environment: Inositol phosphates are the dominant identified soil organic P and are stabilized by mineral sorption. (confidence 0.8)
Roots and microbes exude citrate, malate and oxalate and extrude H+ to desorb phosphate from Fe and Al oxides and dissolve Ca phosphates
Plant rootsMicrobesOrganic acidsHydrogen ionsIron oxidesPhosphate
Evidence (1) · added by Ember
  • Jones 1998, Plant and Soil 205:25, Organic acids in the rhizosphere: a critical review: Citrate and other carboxylates mobilize P by ligand exchange and chelation of Fe and Al. (confidence 0.85)
Phosphate-solubilizing bacteria (Pseudomonas, Bacillus) form gluconic acid via PQQ-glucose dehydrogenase; field inoculation responses are inconsistent
PseudomonasBacillusOrganic acidsPhosphate
Evidence (1) · added by Ember
  • Rodriguez & Fraga 1999, Biotechnology Advances 17:319, Phosphate solubilizing bacteria and their role in plant growth promotion: Gluconic acid production by PQQ-dependent glucose dehydrogenase is the best-documented solubilization mechanism. (confidence 0.8)
Released phosphate is re-adsorbed to Fe and Al oxides within minutes to hours, so uptake must compete with fast sorption
Iron oxidesAluminum oxidesPlant rootsPhosphateIron oxides
Evidence (1) · added by Ember
  • Hinsinger 2001, Plant and Soil 237:173, Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review: Phosphate sorption is rapid, then slows, so root-released P is short-lived. (confidence 0.7)
Microbial biomass holds a few percent of total soil P but turns over fast, so microbes immobilize and release a large P flux
Soil microbesPhosphorusSoil organic matter
Evidence (1) · added by Ember
  • Brookes, Powlson & Jenkinson 1984, Soil Biology and Biochemistry 16:169, Phosphorus in the soil microbial biomass: Microbial biomass P is a small fraction (about 1-5%) of total soil P but exchanges rapidly with the available pool. (confidence 0.55)
Roots take up Phosphate by high-affinity PHT1 transporters, directly or through mycorrhizal hyphae
Plant rootsMycorrhizal fungiPhosphate
Evidence (1) · added by Ember
  • Raghothama 1999, Annual Review of Plant Physiology and Plant Molecular Biology 50:665: High-affinity PHT1 phosphate transporters are induced under P deficiency. (confidence 0.8)
Rising phosphate supply represses starvation responses, lowering phosphatase and organic acid release
Plant rootsMicrobesPhosphate
Evidence (1) · added by Ember
  • Richardson & Simpson 2011, Plant Physiology 156:989: Phosphatase and carboxylate release are induced by P deficiency and repressed when P is sufficient. (confidence 0.7)