Water RelationsWater RelationsChapter 5Chapter 5

鄭先祐鄭先祐 (Ayo)(Ayo)

靜宜大學 生態學系靜宜大學 生態學系

Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/

Email add: Japalura@hotmail.com

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OutlineOutline Water AvailabilityWater Availability Water Content of AirWater Content of Air Water Movement in Aquatic EnvironmentsWater Movement in Aquatic Environments Water Movement Between Soils and Water Movement Between Soils and

PlantsPlants Water Regulation on LandWater Regulation on Land Water Acquisition by AnimalsWater Acquisition by Animals Water Acquisition by PlantsWater Acquisition by Plants Water Conservation by Plants and AnimalsWater Conservation by Plants and Animals Water and Salt Balance in Aquatic Water and Salt Balance in Aquatic

EnvironmentsEnvironments

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Water AvailabilityWater Availability

The tendency of water to move down The tendency of water to move down concentration gradients, and the concentration gradients, and the magnitude of those gradients, magnitude of those gradients, determine whether an organism determine whether an organism tends to lose or gain water from its tends to lose or gain water from its environment.environment. Must consider an organism’s Must consider an organism’s

microclimate (microclimate ( 微氣候微氣候 ) in order to ) in order to understand its water relations.understand its water relations.

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Water Content of AirWater Content of Air

Evaporation accounts for much of Evaporation accounts for much of water lost by terrestrial organisms.water lost by terrestrial organisms. As water vapor in the air increases, the As water vapor in the air increases, the

water concentration gradient from water concentration gradient from organisms to air is reduced, thus organisms to air is reduced, thus evaporative loss is decreased.evaporative loss is decreased. Evaporative coolers work best in dry Evaporative coolers work best in dry

climates.climates.

於乾燥的氣候，蒸發的冷卻效果最好。於乾燥的氣候，蒸發的冷卻效果最好。

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Water Content of AirWater Content of Air Relative HumidityRelative Humidity: (: ( 相對溼度相對溼度 ))

Water Vapor DensityWater Vapor Density

Saturation Water Vapor Density Saturation Water Vapor Density (x 100)(x 100)

Water vapor density is measured as the Water vapor density is measured as the water vapor per unit volume of air.water vapor per unit volume of air.

Saturation water vapor density is Saturation water vapor density is measured as the quantity of water measured as the quantity of water vapor air can potentially hold.vapor air can potentially hold. Changes with temperature.Changes with temperature.

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Water Content of AirWater Content of Air

Total Atmospheric Pressure (Total Atmospheric Pressure ( 大氣壓大氣壓 )) Pressure exerted by all gases in the air.Pressure exerted by all gases in the air.

Water Vapor Pressure (Water Vapor Pressure ( 水氣壓水氣壓 )) Partial pressure due to water vapor.Partial pressure due to water vapor.

Saturation Water Vapor Pressure (Saturation Water Vapor Pressure ( 飽飽和水氣壓和水氣壓 )) Pressure exerted by water vapor in air Pressure exerted by water vapor in air

saturated by water.saturated by water. Vapor Pressure Deficit (Vapor Pressure Deficit ( 水氣壓赤字水氣壓赤字 ))

Difference between WVP and SWVP at a Difference between WVP and SWVP at a particular temperature.particular temperature.

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Evaporative Water LossEvaporative Water Loss

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Water Movement in Water Movement in Aquatic Environments Aquatic Environments

(( 水域環境水域環境 )) Water moves down concentration Water moves down concentration

gradient.gradient. Water is more concentrated in freshwater Water is more concentrated in freshwater (( 淡水淡水 ) environments than in the oceans.) environments than in the oceans.

Aquatic organisms can be viewed as an Aquatic organisms can be viewed as an aqueous solution bounded by a aqueous solution bounded by a selectively permeable membrane selectively permeable membrane floating in an another aqueous solution.floating in an another aqueous solution.

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Water Movement in Water Movement in Aquatic EnvironmentsAquatic Environments

If two environments differ in water If two environments differ in water or salt concentrations, substances or salt concentrations, substances will tend to move down their will tend to move down their concentration gradients.concentration gradients. Diffusion (Diffusion ( 擴散擴散 )) Osmosis (Osmosis ( 滲透滲透 )): Diffusion through a : Diffusion through a

semipermeable membrane.semipermeable membrane.

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Water Movement in Water Movement in Aquatic EnvironmentAquatic Environment

Isomotic (Isomotic ( 同等同等 )): Body fluids and : Body fluids and external fluid are at the same external fluid are at the same concentration.concentration.

Hypo-osmotic(Hypo-osmotic( 低低 )): Body fluids are at : Body fluids are at a higher concentration than the a higher concentration than the external environment.external environment.

Hyper-osmotic(Hyper-osmotic( 高高 )): Body fluids are : Body fluids are at a lower concentration than the at a lower concentration than the external environment.external environment.

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Water Movement Between Water Movement Between Soils and PlantsSoils and Plants

Water moving between soil and plants Water moving between soil and plants flows down a water potential gradient.flows down a water potential gradient.

Water potential (Water potential () is the capacity to ) is the capacity to perform work.perform work. Dependent on free energy content.Dependent on free energy content. Pure Water Pure Water = 0. = 0.

in nature generally negative.in nature generally negative. solutesolute measures the reduction in measures the reduction in due to due to

dissolved substances.dissolved substances.

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Water Movement Between Water Movement Between Soils and PlantsSoils and Plants

plantplant = = solutesolute + + matricmatric + + pressurepressure

Matric ForcesMatric Forces: Water’s tendency to : Water’s tendency to adhere to container walls.adhere to container walls.

pressure pressure is the reduction in water potential is the reduction in water potential due to negative pressure created by due to negative pressure created by water evaporating from leaves.water evaporating from leaves.

As long as As long as plantplant > > soilsoil, water flows from , water flows from the soil to the plant.the soil to the plant.

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Water Regulation on Water Regulation on LandLand

Terrestrial organisms face (2) major Terrestrial organisms face (2) major challenges:challenges: Evaporative loss to environment.Evaporative loss to environment. Reduced access to replacement water.Reduced access to replacement water.

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Water Regulation on Water Regulation on Land - AnimalsLand - Animals

WWiaia= W= Wdd + W + Wff + W + Waa - W - Wee - W - Wss

WWiaia= Animal’s internal water= Animal’s internal water

WWdd = Drinking = Drinking

WWff = Food = Food

WWaa = Absorbed by air = Absorbed by air

WWee = Evaporation = Evaporation

WWss = Secretion / Excretion = Secretion / Excretion

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Water Regulation on Water Regulation on Land - AnimalsLand - Animals

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Water Regulation on Water Regulation on Land - PlantsLand - Plants

WWipip= W= Wrr + W + Waa - W - Wtt - W - Wss

WWipip= Plant’s internal water= Plant’s internal water

WWrr =Roots =Roots

WWaa = Air = Air

WWtt = Transpiration = Transpiration

WWss = Secretions = Secretions

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Water Regulation on Land Water Regulation on Land - Plants- Plants

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Water Acquisition by Water Acquisition by AnimalsAnimals

Most terrestrial animals satisfy their Most terrestrial animals satisfy their water needs via eating and drinking.water needs via eating and drinking. Can also be gained via metabolism Can also be gained via metabolism

through oxidation of glucose:through oxidation of glucose: CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22OO Metabolic waterMetabolic water refers to the water refers to the water

released during cellular respiration.released during cellular respiration.

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Water Acquisition by Water Acquisition by PlantsPlants

Extent of plant root development Extent of plant root development often reflects differences in water often reflects differences in water availability.availability. Deeper roots often help plants in dry Deeper roots often help plants in dry

environments extract water from deep environments extract water from deep within the soil profile.within the soil profile.

ParkPark found supportive evidence via found supportive evidence via studies conducted on common Japanese studies conducted on common Japanese grasses, grasses, Digitaria adscendensDigitaria adscendens and and Eleusine indica.Eleusine indica.

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Water Conservation by Water Conservation by Plants and AnimalsPlants and Animals

Many terrestrial organisms equipped Many terrestrial organisms equipped with waterproof (with waterproof ( 不透水不透水 ) outer covering.) outer covering.

Concentrated urine / feces.Concentrated urine / feces. Condensing water vapor in breath.Condensing water vapor in breath. Behavioral modifications to avoid stress Behavioral modifications to avoid stress

times.times. Drop leaves in response to drought.Drop leaves in response to drought. Thick leavesThick leaves Few stomataFew stomata Periodic dormancyPeriodic dormancy

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Dissimilar Organisms Dissimilar Organisms with Similar Approaches with Similar Approaches

to Desert Lifeto Desert Life CamelsCamels

Can withstand water loss up to 20%.Can withstand water loss up to 20%. Face into sun to reduce exposure.Face into sun to reduce exposure. Thick hair: Increased body temperature Thick hair: Increased body temperature

lowers heat gradient.lowers heat gradient.

Saguaro CactusSaguaro Cactus Trunk / arms act as water storage organs.Trunk / arms act as water storage organs. Dense network of shallow roots.Dense network of shallow roots. Reduces evaporative loss.Reduces evaporative loss.

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Two Arthropods with Two Arthropods with Opposite Approaches to Opposite Approaches to

Desert LifeDesert Life ScorpionsScorpions

Slow down, conserve, and stay out of sun. Slow down, conserve, and stay out of sun. Long-lived Long-lived Low metabolic ratesLow metabolic rates

CicadasCicadas ( (Diceroprocta apacheDiceroprocta apache) ) Active on hottest days. Active on hottest days. Perch on branch tips (cooler Perch on branch tips (cooler

microclimates). microclimates). Reduce abdomen temp by feeding on xylem Reduce abdomen temp by feeding on xylem

fluid of pinyon pine trees.fluid of pinyon pine trees.

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Water and Salt Balance in Water and Salt Balance in Aquatic EnvironmentsAquatic Environments

Marine Fish and InvertebratesMarine Fish and Invertebrates Isomotic organisms do not have to expend Isomotic organisms do not have to expend

energy overcoming osmotic gradient.energy overcoming osmotic gradient. Sharks, skates, rays - Elevate blood solute Sharks, skates, rays - Elevate blood solute

concentrations hyperosmotic to seawater.concentrations hyperosmotic to seawater. Slowly gain water osmotically.Slowly gain water osmotically.

Marine bony fish are strongly hypo-Marine bony fish are strongly hypo-osmotic, thus need to drink seawater for osmotic, thus need to drink seawater for salt influx.salt influx.

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Osmoregulation by Marine Osmoregulation by Marine OrganismsOrganisms

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Water and Salt Balance in Water and Salt Balance in Aquatic EnvironmentsAquatic Environments

Freshwater Fish and InvertebratesFreshwater Fish and Invertebrates Hyper-osmotic organisms that Hyper-osmotic organisms that

excrete excess internal water via excrete excess internal water via large amounts of dilute urine.large amounts of dilute urine. Replace salts by absorbing sodium and Replace salts by absorbing sodium and

chloride at base of gill filaments and by chloride at base of gill filaments and by ingesting food.ingesting food.

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Osmoregulation by Freshwater Osmoregulation by Freshwater OrganismsOrganisms

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Applications & ToolsApplications & Tools

Stable isotope analysisStable isotope analysis Stable isotopes of hydrogen include Stable isotopes of hydrogen include

11H and H and 22H, which is generally H, which is generally designated as D, an abbreviation of designated as D, an abbreviation of deuterium.deuterium.

Stable isotopes of carbon, for Stable isotopes of carbon, for example, include example, include 1313C and C and 1212C.C.

to study water uptake by plantsto study water uptake by plants

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ReviewReview Water AvailabilityWater Availability Water Content of AirWater Content of Air Water Movement in Aquatic EnvironmentsWater Movement in Aquatic Environments Water Movement Between Soils and Water Movement Between Soils and

PlantsPlants Water Regulation on LandWater Regulation on Land Water Acquisition by AnimalsWater Acquisition by Animals Water Acquisition by PlantsWater Acquisition by Plants Water Conservation by Plants and AnimalsWater Conservation by Plants and Animals Water and Salt Balance in Aquatic Water and Salt Balance in Aquatic

EnvironmentsEnvironments

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