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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Nutrient availability and leaching / Soil sulfur cycling

Soil sulfur cycling

How sulfur enters soil, cycles among organic, sulfate and sulfide forms and leaves by leaching, uptake or gas emission.

Boundary: where this process starts

Starts with: Sulfate enters from rain and dry deposition, gypsum and sulfide weathering, and fertilizer

Boundary: where it ends

Ends after: Volatile sulfur (H2S, dimethyl sulfide) escapes from wet soil to the air; Sulfate leaches with calcium, magnesium and potassium into drainage water

PARTICIPANTSRESOURCESSoil microbesPlant rootsSulfate-reducingbacteriaSulfur-oxidizingbacteriaAtmosphereOtherparticipantsSulfateSulfurCarbonWaterHydrogen ionsImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.adsorbedImpact +3 of 5. Click for details and evidence.solution sulfateImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.55% biological (C-driven)Impact +3 of 5. Click for details and evidence.45% biochemical (S-limited)Impact +3 of 5. Click for details and evidence.mineralized sulfate joins thImpact +3 of 5. Click for details and evidence.hydrolysed sulfate joins theImpact +3 of 5. Click for details and evidence.↻ reinforces · moderate · 0.4 plant litter aImpact +2 of 5. Click for details and evidence.↻ balances · moderate · 0.3 root exudates anImpact -3 of 5. Click for details and evidence.excess over uptake and adsorImpact -3 of 5. Click for details and evidence.waterloggingImpact -4 of 5. Click for details and evidence.drainage re-exposes sulfideImpact +3 of 5. Click for details and evidence.↻ balances · weak · 0.2 sulfate regeneratedImpact -1 of 5. Click for details and evidence.gaseous escapeImpact -1 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 -2 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.↻ balances · moderate · 0.3 desorption returImpact +2 of 5. Click for details and evidence.adsorbed sulfate desorbs forSulfate enters from rain and dry deposition, gypsum and sulfide weathering, and fertilizer: makes SulfatemakesSulfate enters from rain and dry deposition, gypsum and sulfide weathering, and fertilizer: uses WaterMost topsoil sulfur is organic (ester sulfates and C-bonded S), often 90-95% of total S: uses SulfurFork: how organic sulfur is released: uses SulfateFork: how organic sulfur is released: uses SulfurFork: how organic sulfur is released: uses CarbonMicrobes oxidize carbon and release C-bonded S as sulfate along with CO2: makes SulfatemakesMicrobes oxidize carbon and release C-bonded S as sulfate along with CO2: uses up Carbonuses upArylsulfatase hydrolyses ester sulfates when sulfate is scarce: makes SulfatemakesArylsulfatase hydrolyses ester sulfates when sulfate is scarce: uses up Sulfuruses upSulfate in solution is adsorbed on Fe and Al oxides and edge sites, desorbing as pH rises: uses SulfateSulfate in solution is adsorbed on Fe and Al oxides and edge sites, desorbing as pH rises: uses Hydrogen ionsRoots and mycorrhizal hyphae take up sulfate (plant S need is roughly 1/10 of N need): uses up Sulfateuses upRoots and mycorrhizal hyphae take up sulfate (plant S need is roughly 1/10 of N need): uses up Sulfuruses upSulfate leaches with calcium, magnesium and potassium into drainage water: uses up Sulfateuses upSulfate leaches with calcium, magnesium and potassium into drainage water: uses WaterIn waterlogged soil, sulfate-reducing bacteria turn sulfate into sulfide that precipitates with iron: uses up Sulfateuses upIn waterlogged soil, sulfate-reducing bacteria turn sulfate into sulfide that precipitates with iron: makes SulfurmakesIn waterlogged soil, sulfate-reducing bacteria turn sulfate into sulfide that precipitates with iron: uses up Carbonuses upDrainage or drought re-exposes sulfide, which Thiobacillus oxidizes to sulfuric acid: makes SulfatemakesDrainage or drought re-exposes sulfide, which Thiobacillus oxidizes to sulfuric acid: uses up Sulfuruses upDrainage or drought re-exposes sulfide, which Thiobacillus oxidizes to sulfuric acid: makes Hydrogen ionsmakesVolatile sulfur (H2S, dimethyl sulfide) escapes from wet soil to the air: uses up Sulfuruses updelivered to soilsurfaceSulfate: delivered to soil surfacecarries depositedsulfateWater: carries deposited sulfatemostly locked in organicformSulfur: mostly locked in organic formshapes which routeappliesSulfate: shapes which route appliessplit between tworelease routesSulfur: split between two release routesoxidized to releasesulfurCarbon: oxidized to release sulfurreleased into soilsolutionSulfate: released into soil solutionoxidized by microbesCarbon: oxidized by microbesreleased when sulfate isscarceSulfate: released when sulfate is scarcehydrolysed from esterbondsSulfur: hydrolysed from ester bondsadsorbed onto mineralsurfacesSulfate: adsorbed onto mineral surfacespH controls adsorptionand desorptionHydrogen ions: pH controls adsorption and desorptiontaken up by roots andhyphaeSulfate: taken up by roots and hyphaeassimilated into planttissueSulfur: assimilated into plant tissueleached as anion withcationsSulfate: leached as anion with cationstransports leachedsolutesWater: transports leached solutesreduced by anaerobicbacteriaSulfate: reduced by anaerobic bacteriaformed as sulfideSulfur: formed as sulfideoxidized as electrondonorCarbon: oxidized as electron donorformed by oxidationSulfate: formed by oxidationre-exposed and oxidizedSulfur: re-exposed and oxidizedreleased into soil waterHydrogen ions: released into soil watervolatilized from wetsoilSulfur: volatilized from wet soilStart: Sulfur entersthe soil as sulfate ororganic SSTARTStart: Sulfur enters the soil as sulfate or organic SEnd: Sulfur taken up,lost or locked awayENDEnd: Sulfur taken up, lost or locked awaySulfate enters fromrain and drydeposition, gypsum a…👍1📄1Sulfate enters from rain and dry deposition, gypsum and sulfide weathering, and fertilizerMost topsoil sulfur isorganic (ester sulfatesand C-bonded S), oft…👍1📄1Most topsoil sulfur is organic (ester sulfates and C-bonded S), often 90-95% of total SFork: how organicsulfur is released📄1Fork: how organic sulfur is releasedMicrobes oxidize carbonand release C-bonded Sas sulfate along wi…📄1Microbes oxidize carbon and release C-bonded S as sulfate along with CO2Arylsulfatasehydrolyses estersulfates when sulfa…📄1Arylsulfatase hydrolyses ester sulfates when sulfate is scarceSulfate in solution isadsorbed on Fe and Aloxides and edge site…👍1📄1Sulfate in solution is adsorbed on Fe and Al oxides and edge sites, desorbing as pH risesRoots and mycorrhizalhyphae take up sulfate(plant S need …👍1📄1Roots and mycorrhizal hyphae take up sulfate (plant S need is roughly 1/10 of N need)Sulfate leaches withcalcium, magnesium andpotassium into draina…👍1📄1 ↗1Sulfate leaches with calcium, magnesium and potassium into drainage waterIn waterlogged soil,sulfate-reducingbacteria turn sulfa…👍1📄1In waterlogged soil, sulfate-reducing bacteria turn sulfate into sulfide that precipitates with ironDrainage or droughtre-exposes sulfide,which Thiobacill…👍1📄1 ↗1Drainage or drought re-exposes sulfide, which Thiobacillus oxidizes to sulfuric acidVolatile sulfur (H2S,dimethyl sulfide)escapes from wet so…📄1Volatile sulfur (H2S, dimethyl sulfide) escapes from wet soil to the air
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)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Sulfate enters from rain and dry deposition, gypsum and sulfide weathering, and fertilizer
RainAtmosphereParent rockSulfateWater
Evidence (1) · added by Cinder-B
  • Likens et al. 2002, Biogeochemistry 60:235-316 (Hubbard Brook sulfur budget): Atmospheric deposition was the dominant S input at Hubbard Brook, with weathering a small share. (confidence 0.8)
Most topsoil sulfur is organic (ester sulfates and C-bonded S), often 90-95% of total S
Soil organic matterSoil microbesSulfurSoil organic matter
Evidence (1) · added by Cinder-B
  • Scherer 2009, Sulfur in soils, J. Plant Nutrition and Soil Science 172:326-335: In most aerated agricultural soils organic S forms are the large majority of total S (range roughly 90-98%). (confidence 0.8)
⑂ Fork: how organic sulfur is released
Soil microbesArylsulfatase enzymesSulfurCarbonSulfate
Evidence (1) · added by Cinder-B
  • McGill & Cole 1981, Comparative aspects of cycling of organic C, N, S and P through soil organic matter, Geoderma 26:267-286: S is released either biologically (C-bonded S mineralized with C oxidation) or biochemically (ester sulfates hydrolysed when S is short). Shares are an estimate, range 40-70% for the biological route. (confidence 0.55)
Microbes oxidize carbon and release C-bonded S as sulfate along with CO2
DecomposersSulfateCarbon dioxideCarbon
Evidence (1) · added by Cinder-B
  • Kertesz & Mirleau 2004, The role of soil microbes in plant sulphur nutrition, J. Experimental Botany 55:1939-1945: Heterotrophs mineralize organic S as a by-product of carbon oxidation when C:S is low. (confidence 0.75)
Arylsulfatase hydrolyses ester sulfates when sulfate is scarce
Arylsulfatase enzymesRhizosphere microbesPlant rootsSulfateSulfur
Evidence (1) · added by Cinder-B
  • Kertesz & Mirleau 2004, J. Experimental Botany 55:1939-1945: Sulfatase and desulfonation genes are induced under sulfate limitation in the rhizosphere. (confidence 0.75)
Sulfate in solution is adsorbed on Fe and Al oxides and edge sites, desorbing as pH rises
Iron oxidesAluminum oxidesSoil solutionSulfateIron oxidesHydrogen ions
Evidence (1) · added by Cinder-B
  • Harward & Reisenauer 1966, Reactions and movement of inorganic soil sulfur, Soil Science 101:326-335: Sulfate adsorption rises with acidity and with oxide content, strongest below about pH 6 in subsoils. (confidence 0.75)
Roots and mycorrhizal hyphae take up sulfate (plant S need is roughly 1/10 of N need)
Plant rootsMycorrhizal fungiSulfateSulfur
Evidence (1) · added by Cinder-B
  • Marschner, Mineral Nutrition of Higher Plants, 3rd ed. (2012), chapter on sulfur: Plants take up sulfate by H+-coupled transporters; crop S content is typically 0.1-0.5% of dry matter, about a tenth of N. (confidence 0.8)
Sulfate leaches with calcium, magnesium and potassium into drainage water
Drainage waterGroundwaterSulfateCalciumMagnesiumPotassiumWater
Evidence (1) · added by Cinder-B
  • Johnson & Cole 1980, Anion mobility in soils: relevance to nutrient transport from forest ecosystems, Environment International 3:79-90: Mobile anions such as sulfate and nitrate carry base cations out of the root zone in equivalent amounts. (confidence 0.8)
In waterlogged soil, sulfate-reducing bacteria turn sulfate into sulfide that precipitates with iron
Sulfate-reducing bacteriaIron-reducing bacteriaSulfateIronCarbonSulfur
Evidence (1) · added by Cinder-B
  • Postgate, The Sulphate-Reducing Bacteria, 2nd ed. (1984), Cambridge Univ. Press: Desulfovibrio-type bacteria use sulfate as terminal electron acceptor once oxygen and nitrate are used up (Eh below about -150 mV). (confidence 0.8)
Drainage or drought re-exposes sulfide, which Thiobacillus oxidizes to sulfuric acid
Sulfur-oxidizing bacteriaSulfurSulfateHydrogen ionsOxygen
Evidence (1) · added by Cinder-B
  • Dent & Pons 1995, A world perspective on acid sulphate soils, Geoderma 67:263-276: Oxidation of pyrite in drained coastal soils can drop pH below 4 (acid sulfate soils). (confidence 0.85)
Volatile sulfur (H2S, dimethyl sulfide) escapes from wet soil to the air
Sulfate-reducing bacteriaAtmosphereSulfurHydrogen sulfide
Evidence (1) · added by Cinder-B
  • Andreae & Jaeschke 1992, Exchange of sulphur between biosphere and atmosphere, in Howarth et al. (eds) Sulphur Cycling on the Continents, SCOPE 48: Soils emit small amounts of reduced S gases; terrestrial biogenic S emission is a minor part of the global S budget. (confidence 0.6)