Water Balance in Terrestrial Plants. Water Regulation on Land - Plants W ip = W r + W a - W t - W s ...

Water Balance in Terrestrial PlantsWater Balance in Terrestrial Plants

Water Regulation on Land - PlantsWater Regulation on Land - 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

Water Regulation on Land - Plants

Water Balance in Terrestrial PlantsWater Balance in Terrestrial Plants

Gain water through rootsGain water through roots Lose waterLose water

through photosynthesis (<1% loss this way)through photosynthesis (<1% loss this way) through transpiration (stomates open to allow through transpiration (stomates open to allow

exchange of COexchange of CO22 and O and O22; water escapes ; water escapes

when guard cells are open)when guard cells are open) transpiration also providestranspiration also provides

transport of nutrientstransport of nutrients coolingcooling

Water Movement Between Soils Water Movement Between Soils and Plantsand 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 (ΨΨ) 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 ψψ = 0. = 0.

ΨΨ in nature generally negative. in nature generally negative. ΨΨsolute measures the reduction in solute measures the reduction in ΨΨ due to due to

dissolved substances.dissolved substances.

Variation in Water AvailabilityVariation in Water AvailabilityWater flows along energy gradients.Water flows along energy gradients. Gravity—water flows downhill. The Gravity—water flows downhill. The

associated energy is associated energy is gravitational gravitational potentialpotential..

Pressure—from an area of higher Pressure—from an area of higher pressure, to lower. The associated pressure, to lower. The associated energy is energy is pressurepressure (or (or turgorturgor) ) potentialpotential..

Variation in Water AvailabilityVariation in Water Availability Osmotic potentialOsmotic potential—water flows from —water flows from

a region of high concentration (low a region of high concentration (low solute concentration) to a region of low solute concentration) to a region of low concentration (high solute concentration (high solute concentration).concentration).

Matric potentialMatric potential—energy associated —energy associated with attractive forces on surfaces of with attractive forces on surfaces of large molecules inside cells or on large molecules inside cells or on surfaces of soil particles.surfaces of soil particles.

Variation in Water AvailabilityVariation in Water Availability

Water potential is the sum of all these Water potential is the sum of all these energy components. It can be defined as:energy components. It can be defined as:

ΨΨo = osmotic potential (negative value).o = osmotic potential (negative value). ΨΨp = pressure potential.p = pressure potential. ΨΨm = matric potential (negative value).m = matric potential (negative value).

mpo

Water Movement Between Soils Water Movement Between Soils and Plantsand Plants

ΨΨplant = plant = ΨΨsolute + solute + ΨΨmatric + matric + ΨΨpressurepressure

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

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

As long as As long as ΨΨplant < plant < ΨΨsoil, water flows from soil, water flows from the soil to the plant.the soil to the plant.


Water always moves from a system of Water always moves from a system of higher higher ΨΨ to lower to lower ΨΨ, following the energy , following the energy gradient.gradient.

Atmospheric water potential is related to Atmospheric water potential is related to relative humidity. If less than 98%, water relative humidity. If less than 98%, water potential is low relative to organisms. potential is low relative to organisms. Terrestrial organisms must thus prevent Terrestrial organisms must thus prevent water loss to the atmosphere.water loss to the atmosphere.


Resistance—a force that impedes water Resistance—a force that impedes water movement along an energy gradient.movement along an energy gradient.

To resist water loss, terrestrial organisms To resist water loss, terrestrial organisms have waxy cuticles (insects and plants) or have waxy cuticles (insects and plants) or animal skin.animal skin.


Terrestrial plants and soil microorganisms Terrestrial plants and soil microorganisms must take up water from the soil to replace must take up water from the soil to replace water lost to the atmosphere.water lost to the atmosphere.

Water potential of soils is mostly Water potential of soils is mostly dependent on matric potential.dependent on matric potential.

Amount of water in soil is determined by Amount of water in soil is determined by balance of inputs and outputs, soil texture, balance of inputs and outputs, soil texture, and topography.and topography.

Classification of Plants According Classification of Plants According to Habitat Typeto Habitat Type

MesophytesMesophytes

PhreophytesPhreophytes

HalophytesHalophytes

XerophytesXerophytes

HydrophytesHydrophytes

MesophytesMesophytes

Grow where there is a moderate amount of Grow where there is a moderate amount of waterwater

May also have some of the xerophyte adaptations May also have some of the xerophyte adaptations for drought conditionsfor drought conditions

Many of our midwest native treesMany of our midwest native trees

OaksOaks

MaplesMaples

ElmsElms

HickoriesHickories

PhreophytesPhreophytes

Long roots to reach water tableLong roots to reach water table e.g.e.g. mesquite shrubs may have roots 175 feet long mesquite shrubs may have roots 175 feet long Prairie grasses and forbsPrairie grasses and forbs

HalophytesHalophytes

Adapted for high salt environmentsAdapted for high salt environments are able to take up water from soils with high are able to take up water from soils with high

solute concentrationssolute concentrations many do most of their growing during rainy many do most of their growing during rainy

periods when salt conc is lowestperiods when salt conc is lowest desert holly - uses accumulated salt as desert holly - uses accumulated salt as

reflective surface on leavesreflective surface on leaves

Desert Holly Salicornia

Salt glands exuding salt droplets


Plants adapted to dry Plants adapted to dry conditionsconditions

SucculentsSucculents: e.g. Cacti, : e.g. Cacti, euphorbiaseuphorbias Fleshy tissue in which water Fleshy tissue in which water

can be storedcan be stored Waxy leavesWaxy leaves Insulating hairsInsulating hairs

TrichomesTrichomes


Desert EphemeralsDesert Ephemerals Annuals; adaptation is in Annuals; adaptation is in life history strategylife history strategy

Plant activity is limited to periods that are optimal Plant activity is limited to periods that are optimal for growth and development, i.e. After a heavy for growth and development, i.e. After a heavy rain. rain.

Plants die after flowering and producing seedsPlants die after flowering and producing seeds

Produce seed bankProduce seed bank

Seeds remain dormant in the soil (seed bank) until Seeds remain dormant in the soil (seed bank) until the next rains. This may be many years away.the next rains. This may be many years away.

California poppies and other ephemerals from the Mojave Desert of the American Southwest

Blue Phacelia from the Sonoran and Mojave Deserts

Seed Bank

Common Adaptations Common Adaptations Seen in Desert Plants Seen in Desert Plants

Enhanced cuticle, a waxy Enhanced cuticle, a waxy covering, which prevents covering, which prevents water loss.water loss.

Leaves of plants like the Leaves of plants like the Jojoba and Compass Plant Jojoba and Compass Plant face N-S, minimizing face N-S, minimizing exposure to most intense exposure to most intense sunlight. sunlight.

Spines and hairs discourage Spines and hairs discourage herbivores and help shade herbivores and help shade plant. plant.

Spines are leavesSpines are leaves Small narrow leaves Small narrow leaves

decrease heating from the decrease heating from the sun, less surface area for sun, less surface area for water loss. water loss.

Rotating leaves enable the Rotating leaves enable the plant to orient its leaves away plant to orient its leaves away from maximum exposure to from maximum exposure to the sun.the sun.

Paired leaves of Paired leaves of creosote bush can close creosote bush can close to conserve water.to conserve water.

Common Adaptations Common Adaptations Seen in Desert PlantsSeen in Desert Plants


Succulent leaves reduce the surface-to-volume Succulent leaves reduce the surface-to-volume ratio and favor water conservation. ratio and favor water conservation.


TrichomesTrichomes, hair-like , hair-like projections, that projections, that create a thick create a thick boundary layer which boundary layer which will deflect excess will deflect excess light as well as infra light as well as infra red wavelengths. red wavelengths.

A crew of intrepid Biologists with a Haleakala Silversword


Small, hard leavesSmall, hard leaves Drought-deciduousDrought-deciduous

Drop leaves/twigs when soil Drop leaves/twigs when soil dries up. dries up.

OcotilloOcotillo


Long vertical roots enabling a plant to reach water Long vertical roots enabling a plant to reach water sources beneath the soil. sources beneath the soil.

Shallow, radial roots, those which extend horizontally, Shallow, radial roots, those which extend horizontally,

which maximize water absorption at the surface.which maximize water absorption at the surface.

Mesquite


Leaf polymorphism in Leaf polymorphism in which broad leaves are which broad leaves are formed when soil formed when soil moisture is high and moisture is high and narrow leaves follow as narrow leaves follow as that water is used up. that water is used up.

Increased leaf surface Increased leaf surface area which increases the area which increases the rate of heat dissipation.rate of heat dissipation.


Use shady microhabitatsUse shady microhabitats Stomates regulate exchange of gasesStomates regulate exchange of gases

Recessed and reduced stomates which Recessed and reduced stomates which decreases water loss.decreases water loss.

Shade Microhabitats

Aloes in Namib Desert

Lichens on rock in Big Bend Nat’l Park

Hornwort stomate (wet habitat)

Xerophyte stomates

Note countersunk guard cells and thick cuticle

Adaptive Variations of Adaptive Variations of Photosynthesis: Photosynthesis:

CC33, C, C44 & CAM & CAM

PhotosynthesisPhotosynthesis

RUBISCORUBISCO: key enzyme that catalyzes the : key enzyme that catalyzes the reduction of COreduction of CO22 to organic C, but also to organic C, but also

catalyzes the reverse rxn.catalyzes the reverse rxn. Photorespiration -- uses OPhotorespiration -- uses O22 and releases CO and releases CO22

COCO22 enters the leaf through stomates. enters the leaf through stomates.

Open stomata decrease photorespiration, but Open stomata decrease photorespiration, but increase water lossincrease water loss

C3 PhotosynthesisC3 Photosynthesis

Called C3 because the COCalled C3 because the CO22 is first incorporated into a 3- is first incorporated into a 3-carbon compound. carbon compound.

Stomata are open during the day. Stomata are open during the day.

RUBISCO, the enzyme involved in photosynthesis, is also RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of COthe enzyme involved in the uptake of CO22. .

Photosynthesis takes place throughout the leaf. Photosynthesis takes place throughout the leaf.

Adaptive ValueAdaptive Value: more efficient than C4 and CAM plants : more efficient than C4 and CAM plants under cool and moist conditions and under normal light under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no because requires less machinery (fewer enzymes and no specialized anatomy). specialized anatomy).

Most plants are C3. Most plants are C3.

C3 Photosynthesis

CO2 converted to a 3 C compound

Occurs in palisade mesophyll cells


Called C4 because the COCalled C4 because the CO22 is first incorporated is first incorporated into a 4-carbon compound. into a 4-carbon compound.

Stomata are open during the day. Stomata are open during the day.

Uses PEP Carboxylase for the enzyme involved Uses PEP Carboxylase for the enzyme involved in the uptake of COin the uptake of CO22. This enzyme allows CO. This enzyme allows CO22 to to be taken into the plant very quickly, and then it be taken into the plant very quickly, and then it "delivers" the CO"delivers" the CO22 directly to RUBISCO for directly to RUBISCO for photsynthesis. photsynthesis.

Photosynthesis takes place in inner cells Photosynthesis takes place in inner cells (requires special anatomy called Kranz (requires special anatomy called Kranz Anatomy) Anatomy)

C4 Photosynthesis

CO2 converted to a 4C compound in mesophyll cell

RUBISCO operates in bundle sheath cell where CO2 conc. is high.

C4 plants have spatial

separation of the C4 and

C3 pathways of carbon

fixation.

CC44 Plants Plants Grasses, corn, sugar caneGrasses, corn, sugar cane

CC44 photosynthesis photosynthesis COCO22 fixed by mesophyll cells as a C fixed by mesophyll cells as a C44 compound compound

CC44 cpd is transported to adjacent bundle sheath cells cpd is transported to adjacent bundle sheath cells

CC44 cpd is split, and CO cpd is split, and CO22 is refixed by C is refixed by C3 3 pathwaypathway

Keeps COKeeps CO22 level high in bundle sheath cells level high in bundle sheath cells

COCO22 doesn’t leak out through stomates doesn’t leak out through stomates

Since stomates don’t have to open so much don’t lose so Since stomates don’t have to open so much don’t lose so much watermuch water

Very efficient; CVery efficient; C44 plants do better at high temps but plants do better at high temps but

not when temps are below about 40not when temps are below about 40ooCC


Adaptive Value: Adaptive Value: Photosynthesizes faster than C3 plants under Photosynthesizes faster than C3 plants under

high light intensity and high temperatures high light intensity and high temperatures because the CObecause the CO22 is delivered directly to is delivered directly to RUBISCO, not allowing it to grab oxygen and RUBISCO, not allowing it to grab oxygen and undergo photorespiration. undergo photorespiration.

Has better Has better Water Use EfficiencyWater Use Efficiency because PEP because PEP Carboxylase brings in COCarboxylase brings in CO22 faster and so does faster and so does not need to keep stomata open as much (less not need to keep stomata open as much (less water lost by transpiration) for the same water lost by transpiration) for the same amount of COamount of CO22 gain for photosynthesis. gain for photosynthesis.


Stomata can be more closed and Stomata can be more closed and decrease water loss while photorespiration decrease water loss while photorespiration is kept low --spatial separation is kept low --spatial separation

but, this costs extra energy, 2 ATPbut, this costs extra energy, 2 ATP

ATP used to split C4 compoundATP used to split C4 compound

CAM PhotosynthesisCAM Photosynthesis

CAM stands for Crassulacean Acid MetabolismCAM stands for Crassulacean Acid Metabolism Called CAM after the plant family in which it was first Called CAM after the plant family in which it was first

found (Crassulaceae) and because the COfound (Crassulaceae) and because the CO22 is stored is stored in the form of an acid before use in photosynthesis. in the form of an acid before use in photosynthesis.

Stomata open at night (when evaporation rates are Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. usually lower) and are usually closed during the day. The COThe CO22 is converted to an acid and stored during is converted to an acid and stored during the night. During the day, the acid is broken down the night. During the day, the acid is broken down and the COand the CO22 is released to RUBISCO for is released to RUBISCO for photosynthesis photosynthesis

CAM plants include many succulents such as CAM plants include many succulents such as cactuses and agaves and also some orchids and cactuses and agaves and also some orchids and bromeliadsbromeliads

CAM Photosynthesis

C4 pathway used at night when water loss is low

Stomata completely closed during day

Crassulacean acid metabolism plants have a temporal separation of C4 and C3 pathways of

carbon fixation.

Crassulacean acid metabolismCrassulacean acid metabolism (CAM) (CAM)Light and dark reactions of photosynthesis are Light and dark reactions of photosynthesis are uncoupled so stomates are closed during the uncoupled so stomates are closed during the dayday

NightNight

Stomates openStomates open

Take up CO2Take up CO2

Produce Produce crassulacean acidcrassulacean acid

stores CO2 as a stores CO2 as a CC44 acid acid

DayDay

Stomates closedStomates closed

Use stored CO2 for Use stored CO2 for standard Cstandard C33

photosynthesisphotosynthesis


Adaptive Value: Adaptive Value: Better Water Use Better Water Use

Efficiency than C3 plants Efficiency than C3 plants under arid conditions due under arid conditions due to opening stomata at to opening stomata at night when transpiration night when transpiration rates are lower (no rates are lower (no sunlight, lower sunlight, lower temperatures, lower wind temperatures, lower wind speeds, etc.). speeds, etc.).


Plants may CAM-idlePlants may CAM-idle. .

When conditions are extremely arid, CAM plants can just When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given off leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and COin photosynthesis is used for respiration and CO22 given off in given off in

respiration is used for photosynthesis. respiration is used for photosynthesis.

This is a little like a perpetual energy machine, but there are This is a little like a perpetual energy machine, but there are costs associated with running the machinery for respiration costs associated with running the machinery for respiration and photosynthesis so the plant cannot CAM-idle forever. and photosynthesis so the plant cannot CAM-idle forever. But CAM-idling does allow the plant to survive dry spells, But CAM-idling does allow the plant to survive dry spells, and it allows the plant to recover very quickly when water is and it allows the plant to recover very quickly when water is available again (unlike plants that drop their leaves and available again (unlike plants that drop their leaves and twigs and go dormant during dry spells). twigs and go dormant during dry spells).

HydrophytesHydrophytes

Aquatic plantsAquatic plants

Plants may bePlants may be

submerged and free-floatingsubmerged and free-floating

Submerged and anchored to the substrateSubmerged and anchored to the substrate

anchored to the substrate with the upper anchored to the substrate with the upper leaf surfaces exposed to the airleaf surfaces exposed to the air

Free-floatingFree-floating

Hydrophytes maintain Hydrophytes maintain buoyancy by developing buoyancy by developing intercellular spaces that intercellular spaces that can trap gas bubbles. can trap gas bubbles.

Air spaces in a Air spaces in a water lily stemwater lily stem

HETEROPHYLLY Condition where the same organ has a change in form.

The submerged aquatic leaf is simple, (upper diagram) and only three cells thick, while the floating leaf (lower diagram) contains numerous intercellular airspaces and has a columnar mesophyll arrangement.

malate

Water Balance in Terrestrial Plants. Water Regulation on Land - Plants W ip = W r + W a - W t - W s ...

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