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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil gas exchange and redox / Aerenchyma, radial oxygen loss and the oxidised rhizosphere of wetland plants

Aerenchyma, radial oxygen loss and the oxidised rhizosphere of wetland plants

In waterlogged soil, where oxygen diffuses about ten thousand times slower than in air, wetland plants such as rice carry oxygen through air-filled aerenchyma to the roots, and some leaks into the soil. This creates a thin oxic zone that precipitates iron plaque, detoxifies reduced compounds and couples nitrification to denitrification.

Boundary: where this process starts

Starts with: Waterlogging fills pores, and gas diffusion in water is roughly 10,000 times slower than in air, so soil goes anoxic within hours to days

Boundary: where it ends

Ends after: Fe2+ is oxidised at the root surface and precipitates as an iron plaque that adsorbs phosphate and trace elements; In the oxic zone nitrifiers make nitrate that diffuses to anoxic soil and is denitrified, so a large share of applied nitrogen (an estimated 20 to 50 percent) is lost

PARTICIPANTSRESOURCESPlant rootsIron-reducingbacteriaRice andwetland plantsAerenchymaSoil waterOtherparticipantsOxygenWaterIronPore spaceIron oxidesImpact -4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Low oxygen drives aerenchymaImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.↻ reinforces · weak · 0.2 Healthy roots keepImpact 02 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Waterlogging fills pores, and gas diffusion in water is roughly 10,000 times slower than in air, so soil goes anoxic within hours to days: uses up Oxygenuses upWaterlogging fills pores, and gas diffusion in water is roughly 10,000 times slower than in air, so soil goes anoxic within hours to days: uses WaterWaterlogging fills pores, and gas diffusion in water is roughly 10,000 times slower than in air, so soil goes anoxic within hours to days: uses Pore spaceWetland plants form aerenchyma (root gas space of tens of percent, up to about 40 to 50 percent in rice) that carries oxygen from shoot to root: uses OxygenRadial oxygen loss leaks Oxygen into the soil, forming an oxidised zone a millimetre or so thick around roots: makes OxygenmakesRadial oxygen loss leaks Oxygen into the soil, forming an oxidised zone a millimetre or so thick around roots: uses WaterFe2+ is oxidised at the root surface and precipitates as an iron plaque that adsorbs phosphate and trace elements: uses up Ironuses upFe2+ is oxidised at the root surface and precipitates as an iron plaque that adsorbs phosphate and trace elements: makes Iron oxidesmakesOxidation removes toxic Fe2+, sulfide and organic acids that otherwise injure roots in flooded soil: uses up Ironuses updepleted as diffusionstallsOxygen: depleted as diffusion stallsfills pores and slowsgasWater: fills pores and slows gasfilled, blocking gasmovementPore space: filled, blocking gas movementcarried throughgas-filled rootsOxygen: carried through gas-filled rootsleaks into surroundingsoilOxygen: leaks into surrounding soiloxidises soil aroundrootsWater: oxidises soil around rootsoxidised to form plaqueIron: oxidised to form plaqueprecipitate on rootsurfacesIron oxides: precipitate on root surfacesoxidised and removedIron: oxidised and removedStart: Aerenchyma,radial oxygen loss andthe oxidis…STARTStart: Aerenchyma, radial oxygen loss and the oxidised rhizosphere of wetland plantsEnd: Aerenchyma, radialoxygen loss and theoxidised rhizosphere …ENDEnd: Aerenchyma, radial oxygen loss and the oxidised rhizosphere of wetland plantsWaterlogging fillspores, and gasdiffusion in water …📄1Waterlogging fills pores, and gas diffusion in water is roughly 10,000 times slower than in air, so soil goes anoxic within hours to daysWetland plants formaerenchyma (root gasspace of tens …👍1📄1Wetland plants form aerenchyma (root gas space of tens of percent, up to about 40 to 50 percent in rice) that carries oxygen from shoot to rootRadial oxygen lossleaks Oxygen into thesoil, forming …📄1Radial oxygen loss leaks Oxygen into the soil, forming an oxidised zone a millimetre or so thick around rootsFe2+ is oxidised at theroot surface andprecipitates as an ir…📄1Fe2+ is oxidised at the root surface and precipitates as an iron plaque that adsorbs phosphate and trace elementsIn the oxic zonenitrifiers make nitratethat diffuses to anox…📄1In the oxic zone nitrifiers make nitrate that diffuses to anoxic soil and is denitrified, so a large share of applied nitrogen (an estimated 20 to 50 percent) is lostOxidation removes toxicFe2+, sulfide andorganic acids th…📄1Oxidation removes toxic Fe2+, sulfide and organic acids that otherwise injure roots in flooded soil
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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Resource
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Size of impact
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Subprocess
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Every step, with its evidence

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Waterlogging fills pores, and gas diffusion in water is roughly 10,000 times slower than in air, so soil goes anoxic within hours to days
Soil waterSoil poresOxygenWaterPore space
Evidence (1) · added by Fern
  • Armstrong (1979), Aeration in higher plants, Advances in Botanical Research 7:225-332: Gas diffusion through water-filled pores is about four orders of magnitude slower than through air-filled pores. (confidence 0.8)
Wetland plants form aerenchyma (root gas space of tens of percent, up to about 40 to 50 percent in rice) that carries oxygen from shoot to root
Rice and wetland plantsAerenchymaOxygen
Evidence (1) · added by Fern
  • Colmer (2003), Plant, Cell & Environment 26:17-36: Rice and other wetland species develop root porosity of tens of percent by volume that enables long-distance O2 transport. (confidence 0.8)
Radial oxygen loss leaks Oxygen into the soil, forming an oxidised zone a millimetre or so thick around roots
Plant rootsRhizosphere microbesOxygenWater
Evidence (1) · added by Fern
  • Colmer (2003), Plant, Cell & Environment 26:17-36: Roots without a barrier to radial oxygen loss release O2 to the rhizosphere, which is oxidised at the millimetre scale. (confidence 0.75)
Fe2+ is oxidised at the root surface and precipitates as an iron plaque that adsorbs phosphate and trace elements
Iron plaqueIron-reducing bacteriaIronIron oxidesPhosphate
Evidence (1) · added by Fern
  • Chen, Dixon & Turner (1980), Iron coatings on rice roots: morphology and models of development, Soil Science Society of America Journal 44:1113-1119: Iron oxide coatings on rice roots form by oxidation of Fe2+ using radial oxygen loss. (confidence 0.8)
In the oxic zone nitrifiers make nitrate that diffuses to anoxic soil and is denitrified, so a large share of applied nitrogen (an estimated 20 to 50 percent) is lost
Nitrifying bacteriaDenitrifying bacteriaAmmoniumNitrateNitrous oxideDinitrogen
Evidence (1) · added by Fern
  • Reddy & Patrick (1984), Nitrogen transformations and loss in flooded soils and sediments, CRC Critical Reviews in Environmental Control 13:273-309: Coupled nitrification-denitrification at oxic-anoxic interfaces is a main N loss route in flooded soils; the percentage range is an estimate. (confidence 0.55)
Oxidation removes toxic Fe2+, sulfide and organic acids that otherwise injure roots in flooded soil
Plant rootsIron-reducing bacteriaIronHydrogen sulfideOrganic acids
Evidence (1) · added by Fern
  • Ponnamperuma (1972), The chemistry of submerged soils, Advances in Agronomy 24:29-96: Reduced soils accumulate Fe2+, H2S and organic acids that are toxic to rice at high levels. (confidence 0.8)