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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil-plant-water coupling and drought response

Soil-plant-water coupling and drought response

Coupling between soil water, roots and plant water status during drought. Covers soil drying, falling hydraulic conductivity at the root-soil interface, stomatal closure, hydraulic redistribution and recovery after rain.

Boundary: where this process starts

Starts with: Atmospheric demand pulls water through leaves, creating negative pressure in xylem

Boundary: where it ends

Ends after: Redistributed water supports shallow roots, mycorrhizae and nutrient uptake; Transpired water returns to the air as vapour and cools leaves

PARTICIPANTSRESOURCESPlant rootsStomataSoil waterPlantsXylemOtherparticipantsWaterWater vapourSoil poresMucilageAbscisic acidImpact +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.Impact -3 of 5. Click for details and evidence.Impact -4 of 5. Click for details and evidence.↻ balances · strong · 0.5 Falling supply limImpact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.3 Mucilage buffersImpact +2 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 -4 of 5. Click for details and evidence.↻ balances · strong · 0.6 Stomatal closure lImpact 03 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.70% stomata close in timeImpact -4 of 5. Click for details and evidence.30% tension exceeds the safeImpact -4 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ reinforces · strong · 0.5 Lost conductanceImpact +3 of 5. Click for details and evidence.Impact +2 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 +3 of 5. Click for details and evidence.Water released to dry soil rImpact +3 of 5. Click for details and evidence.Impact 02 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 -4 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.↻ reinforces · weak · 0.2 Vapour loss continAtmospheric demand pulls water through leaves, creating negative pressure in xylem: uses WaterAtmospheric demand pulls water through leaves, creating negative pressure in xylem: uses Water vapourRoots take water up through the root cortex and endodermis: uses WaterSoil water moves to the root along a potential gradient: uses WaterSoil dries near roots as conductivity falls and a gap forms at the root-soil interface: uses WaterSoil dries near roots as conductivity falls and a gap forms at the root-soil interface: makes Soil poresmakesRoots exude mucilage that holds water and eases uptake from dry soil: uses WaterRoots exude mucilage that holds water and eases uptake from dry soil: makes MucilagemakesRoots sense drying and send abscisic acid signals to the shoot: uses WaterRoots sense drying and send abscisic acid signals to the shoot: makes Abscisic acidmakesStomata partly close, reducing transpiration and carbon uptake: uses Water vapourIs the plant drawing water faster than xylem and soil can supply it?: uses WaterStomatal control keeps xylem tension within safe limits: uses WaterXylem cavitation blocks conduits and cuts conductance: uses WaterHydraulic failure leads to leaf shedding and tree mortality: uses WaterDeep roots reach moist subsoil and groundwater: uses WaterRoots move water between wet and dry layers (hydraulic redistribution): uses WaterRedistributed water supports shallow roots, mycorrhizae and nutrient uptake: uses WaterRooting depth tracks the water table and rainfall regime: uses WaterTranspired water returns to the air as vapour and cools leaves: makes Water vapourmakespulled up through xylemWater: pulled up through xylematmospheric demand pullsitWater vapour: atmospheric demand pulls ittaken up through cortexWater: taken up through cortexmoves along potentialgradientWater: moves along potential gradientconductivity falls assoil driesWater: conductivity falls as soil driesforms gaps at rootinterfaceSoil pores: forms gaps at root interfaceeases uptake from drysoilWater: eases uptake from dry soilholds water near rootsMucilage: holds water near rootssensed by rootsWater: sensed by rootssignals drought toshootsAbscisic acid: signals drought to shootsloss reduced as stomatacloseWater vapour: loss reduced as stomata closedemand outpaces supplyWater: demand outpaces supplytension kept within safelimitsWater: tension kept within safe limitsblocks conduits incavitationWater: blocks conduits in cavitationlost in hydraulicfailureWater: lost in hydraulic failurereached by deep rootsWater: reached by deep rootsshuttled between soillayersWater: shuttled between soil layerssupports shallow rootsWater: supports shallow rootsrooting depth tracksavailabilityWater: rooting depth tracks availabilityreleased throughtranspirationWater vapour: released through transpirationStart: Soil-plant-watercoupling and droughtresponseSTARTStart: Soil-plant-water coupling and drought responseEnd: Soil-plant-watercoupling and droughtresponseENDEnd: Soil-plant-water coupling and drought responseAtmospheric demandpulls water throughleaves, creati…📄1Atmospheric demand pulls water through leaves, creating negative pressure in xylemRoots take water upthrough the root cortexand endodermis📄1Roots take water up through the root cortex and endodermisSoil water moves to theroot along a potentialgradient📄1Soil water moves to the root along a potential gradientSoil dries near rootsas conductivity fallsand a gap forms at t…📄1Soil dries near roots as conductivity falls and a gap forms at the root-soil interfaceRoots exude mucilagethat holds water andeases uptake from d…📄1Roots exude mucilage that holds water and eases uptake from dry soilRoots sense drying andsend abscisic acidsignals to the shoot📄1Roots sense drying and send abscisic acid signals to the shootStomata partly close,reducing transpirationand carbon uptake📄1Stomata partly close, reducing transpiration and carbon uptakeIs the plant drawingwater faster than xylemand soil can supply it?📄1Is the plant drawing water faster than xylem and soil can supply it?Stomatal control keepsxylem tension withinsafe limits📄1Stomatal control keeps xylem tension within safe limitsXylem cavitation blocksconduits and cutsconductance📄1Xylem cavitation blocks conduits and cuts conductanceHydraulic failure leadsto leaf shedding andtree mortality📄1Hydraulic failure leads to leaf shedding and tree mortalityDeep roots reach moistsubsoil and groundwater📄1Deep roots reach moist subsoil and groundwaterRoots move waterbetween wet and drylayers (hydraul…📄1Roots move water between wet and dry layers (hydraulic redistribution)Redistributed watersupports shallow roots,mycorrhizae a…📄1Redistributed water supports shallow roots, mycorrhizae and nutrient uptakeRooting depth tracksthe water table andrainfall regime📄1Rooting depth tracks the water table and rainfall regimeTranspired waterreturns to the air asvapour and cools leaves📄1Transpired water returns to the air as vapour and cools leaves
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.

Atmospheric demand pulls water through leaves, creating negative pressure in xylem
AtmosphereLeavesStomataWaterWater vapour
Evidence (1) · added by Ember-B
  • Passioura 1988, Annual Review of Plant Physiology and Plant Molecular Biology 39:245, Water transport in and to roots: Transpiration creates a water potential gradient from soil to leaf along the soil-plant-atmosphere continuum. (confidence 0.7)
Roots take water up through the root cortex and endodermis
Plant rootsAquaporinsWater
Evidence (1) · added by Ember-B
  • Passioura 1988, Annual Review of Plant Physiology and Plant Molecular Biology 39:245, Water transport in and to roots: Radial water flow in roots can be a major resistance and is regulated by aquaporins. (confidence 0.7)
Soil water moves to the root along a potential gradient
Soil waterSoil poresWater
Evidence (1) · added by Ember-B
  • Gardner 1960, Soil Science 89:63, Dynamic aspects of water availability to plants: Water supply to roots depends on soil hydraulic conductivity, which falls steeply as soil dries. (confidence 0.7)
Soil dries near roots as conductivity falls and a gap forms at the root-soil interface
Soil waterPlant rootsWaterSoil pores
Evidence (1) · added by Ember-B
  • Carminati & Javaux 2020, Trends in Plant Science 25:868, Soil rather than xylem vulnerability controls stomatal response to drought: In drying soil, the drop in soil hydraulic conductivity near roots limits uptake before xylem fails. (confidence 0.7)
Roots exude mucilage that holds water and eases uptake from dry soil
Plant rootsRhizosphere microbesMucilageWater
Evidence (1) · added by Ember-B
  • Ahmed, Kroener, Holz, Zarebanadkouki & Carminati 2014, Functional Plant Biology 41:1129, Mucilage exudation facilitates root water uptake in dry soils: Mucilage keeps the rhizosphere wetter than bulk soil and facilitates uptake in dry soil. (confidence 0.7)
Roots sense drying and send abscisic acid signals to the shoot
Plant rootsAbscisic acidAbscisic acidWater
Evidence (1) · added by Ember-B
  • Davies & Zhang 1991, Annual Review of Plant Physiology and Plant Molecular Biology 42:55, Root signals and the regulation of growth and development of plants in drying soil: Roots in drying soil produce ABA that signals soil water status to the leaves independent of leaf water potential. (confidence 0.7)
Stomata partly close, reducing transpiration and carbon uptake
StomataGuard cellsWater vapourCarbon dioxide
Evidence (1) · added by Ember-B
  • Tardieu & Davies 1993, Plant, Cell & Environment 16:341, Integration of hydraulic and chemical signalling in the control of stomatal conductance: Chemical and hydraulic signals jointly set stomatal conductance. (confidence 0.7)
⑂ Is the plant drawing water faster than xylem and soil can supply it?
PlantsXylemWater
Evidence (1) · added by Ember-B
  • Tyree & Sperry 1989, Annual Review of Plant Physiology 40:19, Vulnerability of xylem to cavitation and embolism: If xylem pressure falls below the cavitation threshold, air embolism blocks conduits; share depends on species safety margin; values here are illustrative. (confidence 0.7)
Stomatal control keeps xylem tension within safe limits
StomataXylemWater
Evidence (1) · added by Ember-B
  • Sperry, Adler, Campbell & Comstock 1998, Plant, Cell & Environment 21:347, Limitation of plant water use by rhizosphere and xylem conductance: Stomatal closure limits water loss so that xylem remains conductive. (confidence 0.7)
Xylem cavitation blocks conduits and cuts conductance
XylemAir bubblesWater
Evidence (1) · added by Ember-B
  • Tyree & Sperry 1989, Annual Review of Plant Physiology 40:19, Vulnerability of xylem to cavitation and embolism: Embolism is produced by air entering xylem conduits under high tension and lowers hydraulic conductance. (confidence 0.7)
Hydraulic failure leads to leaf shedding and tree mortality
PlantsXylemWaterCarbon
Evidence (1) · added by Ember-B
  • Anderegg et al. 2016, PNAS 113:5024, Meta-analysis reveals that hydraulic traits explain cross-species patterns of drought-induced tree mortality: Hydraulic safety margins explain cross-species patterns of drought-induced mortality. (confidence 0.7)
Deep roots reach moist subsoil and groundwater
Deep rootsGroundwaterWater
Evidence (1) · added by Ember-B
  • Canadell et al. 1996, Oecologia 108:583, Maximum rooting depth of vegetation types at the global scale: Maximum rooting depths exceed 10 m in some tropical and desert species. (confidence 0.7)
Roots move water between wet and dry layers (hydraulic redistribution)
Plant rootsWater
Evidence (1) · added by Ember-B
  • Richards & Caldwell 1987, Oecologia 73:486, Hydraulic lift: substantial nocturnal water transport between soil layers by Artemisia tridentata roots: Roots move water from wet deep soil to dry shallow soil at night (hydraulic lift) along water potential gradients. (confidence 0.7)
Redistributed water supports shallow roots, mycorrhizae and nutrient uptake
Mycorrhizal fungiShallow rootsSoil microbesWaterNutrients
Evidence (1) · added by Ember-B
  • Caldwell, Dawson & Richards 1998, Oecologia 113:151, Hydraulic lift: consequences of water efflux from the roots of plants: Hydraulic lift keeps shallow roots and microbes active and may extend nutrient uptake in dry topsoil. (confidence 0.7)
Rooting depth tracks the water table and rainfall regime
VegetationWater tableWater
Evidence (1) · added by Ember-B
  • Fan, Miguez-Macho, Jobbagy, Jackson & Otero-Casal 2017, PNAS 114:10572, Hydrologic regulation of plant rooting depth: Global patterns of rooting depth reflect water-table depth and rainfall across landscapes. (confidence 0.7)
Transpired water returns to the air as vapour and cools leaves
AtmosphereLeavesWater vapourHeat
Evidence (1) · added by Ember-B
  • Rodriguez-Iturbe & Porporato 2004, Ecohydrology of Water-Controlled Ecosystems, Cambridge University Press: Transpiration is a major fraction of terrestrial evapotranspiration and cools the canopy. (confidence 0.7)