Lecture #3Water

IntroductionIntroduction

Of all the factors that one has managing in aOf all the factors that one has managing in agreenhouse or greenhouse or interiorscapeinteriorscape, water is the most, water is the mostdifficult. It is an art and a science. difficult. It is an art and a science.

Too much, too little, too soon,Too much, too little, too soon,too late, too cold, too hot, too too late, too cold, too hot, too acidic, too alkaline or too full acidic, too alkaline or too full of certain materials can cause of certain materials can cause death in tropical plants.death in tropical plants.

You must understand how water works and is You must understand how water works and is circulated in plants, to manage it properly. circulated in plants, to manage it properly.

How much water is this tree holding up?How much water is this tree holding up?

Given how much water weighs,Given how much water weighs,there must be a great amount of there must be a great amount of weight generated by water weight generated by water in this tree? in this tree?

How does it get up to the top? How does it get up to the top? There are no pumps in plants! There are no pumps in plants! How does it stay in the plant?How does it stay in the plant?

If a lower branch breaks, why If a lower branch breaks, why doesn’t water come pouring out? doesn’t water come pouring out?

We use gravity to to distribute water to communities.We use gravity to to distribute water to communities.Water towers use strong pumps to slowly bring the water Water towers use strong pumps to slowly bring the water up to a reservoir. The effect of gravity acting on this tank up to a reservoir. The effect of gravity acting on this tank full of water is enhance by forcing the water to flow down full of water is enhance by forcing the water to flow down through a small pipe. The result is massive water pressure!through a small pipe. The result is massive water pressure!

If gravity is such a potent force…If gravity is such a potent force…why doesn’t the water in trees rush out why doesn’t the water in trees rush out of the roots, or spill out of cut branches?of the roots, or spill out of cut branches?

The answer lies blowing in the wind,The answer lies blowing in the wind,within fancy tree anatomy, and in the within fancy tree anatomy, and in the chemical properties of water.chemical properties of water.

Opposite charges attractOpposite charges attractLike charges repelLike charges repel

The first thing to review is the concept of magnetic The first thing to review is the concept of magnetic charges. Many things have positive or negative charges, charges. Many things have positive or negative charges, including magnets and most molecules. “Like” charges including magnets and most molecules. “Like” charges repel each other as is seen in the first video clip below. repel each other as is seen in the first video clip below. “Opposite” magnetic charges are attracted to each other, “Opposite” magnetic charges are attracted to each other, as is demonstrated in the second video clip. Lucky for us, as is demonstrated in the second video clip. Lucky for us, water molecules work in the same way! water molecules work in the same way!

Cohesion Forces

Water molecules have a charge !

+H and +H and O- = +H2O-

+H2O- +H2O- +H2O- +H2O-

Opposite charges attract, and thereforeOpposite charges attract, and thereforewater molecules easily become a chain!water molecules easily become a chain!

If the molecular bond is If the molecular bond is strong enough, and you can pull strong enough, and you can pull one molecule with enough one molecule with enough force, the rest of the water force, the rest of the water chain will follow. chain will follow. This is called cohesion! However, you must However, you must never break the chain! Too never break the chain! Too much force and you can cause much force and you can cause a break in the chain. a break in the chain.

Cohesion Of MoleculesCohesion Of Molecules

Adhesion ForcesCharges on the molecules of plastic in the straw are Charges on the molecules of plastic in the straw are sufficient to pull the water to the sides of the straw. sufficient to pull the water to the sides of the straw. This force is greater than the force of gravity on that This force is greater than the force of gravity on that volume of water. The smaller the straw, the more the side volume of water. The smaller the straw, the more the side charges overcome gravity. Phloem and xylem are very, charges overcome gravity. Phloem and xylem are very, very small tubes, and have a very strong attractive forcevery small tubes, and have a very strong attractive forcecompared to relatively small gravity force exerted on the compared to relatively small gravity force exerted on the very small volume of water.very small volume of water.

Note the Note the raised raised

“meniscus”“meniscus”

Kitchen PaperKitchen Paper Typing PaperTyping PaperToilet PaperToilet Paper

Adhesion/Cohesion PrincipleAdhesion/Cohesion PrincipleFrom which came the “quickerFrom which came the “quicker--pickerpicker--upper!”upper!”

Fibers of xylem quality in paper towels Fibers of xylem quality in paper towels are actually very, very tiny tubes!are actually very, very tiny tubes!

The tubes of xylem are intact and interlaced. If The tubes of xylem are intact and interlaced. If sheets are orientated up and down, the solution will sheets are orientated up and down, the solution will appear to defy gravity. The liquid will move internally appear to defy gravity. The liquid will move internally and externally, fiber to fiber via the forces of and externally, fiber to fiber via the forces of Adhesion and Cohesion, along the water gradient, until Adhesion and Cohesion, along the water gradient, until the entire volume of water weighs more than the holding the entire volume of water weighs more than the holding force of the fibers and the gradient. Then flow stops.force of the fibers and the gradient. Then flow stops.

The Down Fall of Adhesion / Cohesion!The Down Fall of Adhesion / Cohesion!

In drought, or when stems are cut, or when cuttings In drought, or when stems are cut, or when cuttings are taken, the chain of water is broken. There is no are taken, the chain of water is broken. There is no longer a passive supply of new water molecules. The longer a passive supply of new water molecules. The chain of water continues chain of water continues until it evaporates from until it evaporates from the leaves. The remaining the leaves. The remaining water below the breakwater below the breakstops and may slowly stops and may slowly return back to the roots.return back to the roots.

When the water chain is When the water chain is broken, wilting and death broken, wilting and death of the plant part cut off of the plant part cut off from the flow is almost inevitable !from the flow is almost inevitable !

CavitationCavitation

In trees, when the chain In trees, when the chain of water is broken in a of water is broken in a xylem vessel, it makes a xylem vessel, it makes a discernable “pop”. This discernable “pop”. This event is called event is called cavitationcavitation. .

During extreme drought, During extreme drought, sensors can pick up sensors can pick up repetitive repetitive cavitationcavitation in in trees….it can sound like trees….it can sound like a small machine gun!a small machine gun!

EmbolismEmbolism

Now we know how water is held up in trees. We have Now we know how water is held up in trees. We have yet to determine how water is pulled up trees, despite yet to determine how water is pulled up trees, despite the tremendous force of gravity. As there are no pumps, the tremendous force of gravity. As there are no pumps, what could possibly provided enough energy to pull the what could possibly provided enough energy to pull the chains of water molecules up?chains of water molecules up?

The answer The answer is not is not

in this picture!in this picture!

The answer is in this one!The answer is in this one!The force that pulls water to the top of the plantis sun and wind driven evaporation from the leaves!

Temperature affects molecular bonds. TheTemperature affects molecular bonds. Thewarmer the molecule, the faster it moves around.warmer the molecule, the faster it moves around.

If enough heat is applied, the energy causes theIf enough heat is applied, the energy causes thecohesion bonds of water to break. cohesion bonds of water to break.

Plant leaves can become very warm when bright Plant leaves can become very warm when bright light from the sun bombards them. light from the sun bombards them.

This can generate very active water molecules This can generate very active water molecules and increase the number that can break free of the and increase the number that can break free of the chain and become vapor. These molecules can then chain and become vapor. These molecules can then escape to the outside through the numerous stomata in escape to the outside through the numerous stomata in the leaf ! Therefore sunlight enhances evaporation!the leaf ! Therefore sunlight enhances evaporation!

Factor #1 – Sunlight !

Leaf Anatomy Is Very Important!Leaf Anatomy Is Very Important!

A cross section of leavesA cross section of leavesclearly shows the air spacesclearly shows the air spaces

in the spongy parenchyma cells.in the spongy parenchyma cells.

The spongy parenchyma cells are very special. TheseThe spongy parenchyma cells are very special. Theseair spaces allow for gas exchange in addition to providingair spaces allow for gas exchange in addition to providinga membrane surface for water evaporation. Gasses sucha membrane surface for water evaporation. Gasses suchas COas CO2 2 and Oand O22 are freely exchanged. In many ways, are freely exchanged. In many ways, this area of plant tissue acts very much like our lungs. this area of plant tissue acts very much like our lungs.

Factor 2: Gas Exchange & Wind!

For best results, plants need to For best results, plants need to be kept relatively stress free sobe kept relatively stress free sothat that stomates stomates stay open and stay open and allow gasses to exchange freely.allow gasses to exchange freely.A droughtA drought--stricken plant is notstricken plant is notlikely to have optimal gas exchange.likely to have optimal gas exchange.

The air outside the leaf is much dryer that theThe air outside the leaf is much dryer that the

air between the parenchyma cells. The greater the air between the parenchyma cells. The greater the

difference in humidity levels, the faster evaporation difference in humidity levels, the faster evaporation

can occur. can occur.

Transpiration is the term we use to describe theTranspiration is the term we use to describe the

heatheat-- driven, humidity gradientdriven, humidity gradient--enhanced, mechanismenhanced, mechanism

for water evaporation from plant leaves.for water evaporation from plant leaves.

The Leaf Water Pump

Cold Cold HotHot

DiffusionSubstances flow from an area of Substances flow from an area of high concentration, to an area of high concentration, to an area of low concentration.low concentration.

Temperature can affect the speed Temperature can affect the speed of the process, as can differences of the process, as can differences in density or concentration.in density or concentration. Cold Cold HotHot

Cold HotCold Hot Cold HotCold Hot

Number of Stomata Per Square Inch of Leaf

100,000100,00055,00055,000SunflowerSunflower175,000175,00018,00018,000PumpkinPumpkin290,000290,00000OrangeOrange

375,000375,00000Black OakBlack Oak64,00064,00039,00039,000CornCorn160,000160,00026,00026,000BeanBean250,000250,00000AppleApple

Lower EpidermisUpper EpidermisPlant

Mid-Summer Water Loss per Day

PlantA single corn plantA single corn plantA single giant ragweed plantA single giant ragweed plantA single young 10A single young 10--ft apple treeft apple treeA 12A 12--foot columnar cactusfoot columnar cactusA coconut palm in moist tropicsA coconut palm in moist tropicsA date palm living near an oasisA date palm living near an oasis

Water Loss (in quarts)3-46-7

10-200.02

70-80400-500

Water Losses from Single Plants During A Growing Season

35,00035,000365365Date PalmDate Palm

4,2004,200365365CoconutCoconut1,8001,800188188Apple treeApple tree1401409090RagweedRagweed

1251259090SunflowerSunflower

5050100100CornCorn3030100100TomatoTomato

LossDaysPlant

The Pump !

Water is pulled Water is pulled upward by vapor upward by vapor pressure deficit pressure deficit established by the established by the transpiration of transpiration of water from the open water from the open leafleaf stomatesstomates..

The Pump’s Location

Light and Heat DriveThe Process!

Relative HumidityRelative HumidityEffect of relative humidity on a plant leaf Effect of relative humidity on a plant leaf

!! !!

Relative Relative Humidity =Humidity =

Relative Relative Humidity =Humidity =

HH22OO

HH22OO

HH22OO HH22OO

HH22OO

HH22OO

HH22OO707000FF 707000FF

10%10% 50%50%

Relative HumidityRelative HumidityEffect of relative humidity and air temperature on a Effect of relative humidity and air temperature on a

plant leafplant leaf

!! !!

Relative Relative Humidity = 50%Humidity = 50%

Relative Relative Humidity = 50%Humidity = 50%

HH22OO

HH22OO

HH22OO HH22OO

HH22OO

HH22OO

HH22OO909000FF 707000FF

HH22OO

HH22OO

Stomates Regulate Water Loss

Water potential Water potential (water status in (water status in cells) regulates cells) regulates opening and opening and closing of the closing of the stomatesstomates..

Presence or absence of light also regulates thePresence or absence of light also regulates thestomatesstomates. Thus drought can impair leaf gas . Thus drought can impair leaf gas exchange and limit exchange and limit photosynthatephotosynthate production. production.

Many tropical plants require numerous Many tropical plants require numerous stomatesstomates to to allow sufficient water to be drawn out of the leaves allow sufficient water to be drawn out of the leaves under high humidity. under high humidity.

Cacti and many dryCacti and many dry--subtropical plants have fewsubtropical plants have fewstomatesstomates to conserve water. to conserve water.

What happens if a tropical plant is grown in a dry, warm office environment?

What if a cactus is grown in a fairly dark, humid atrium environment?

So Why Worry About Stomates?

Air Movement Drives Nutrient Uptake!

Air movement across the leaf surface strips away Air movement across the leaf surface strips away water molecules that have emerged from the water molecules that have emerged from the stomatesstomates, , intensifying the water loss gradient and speeding up wholeintensifying the water loss gradient and speeding up whole--plant water loss. plant water loss.

As more water is released, more nutrients from the As more water is released, more nutrients from the soil solution are drawn up with the water entering the roots. soil solution are drawn up with the water entering the roots.

Therefore, air movement does more than just keep water moving, it aids in nutrient uptake and distribution in the plant.

So what happens when a plant is put in a small,

cool, dark interiorscape with very little air

movement … and the plant is fertilized weekly?

What happens when a plant is put in a very warm

interiorscape with low humidity, high air movement

and bright sunlight … and fertilized weekly?

You lose money ! You lose money !

WiltingAn early warning sign that there is not sufficient An early warning sign that there is not sufficient water in the plant vascular system is “Wilting.”water in the plant vascular system is “Wilting.”

Water pressure in the cells aids the structural Water pressure in the cells aids the structural strength and integrity of the plant. If strength and integrity of the plant. If evaporation is greater than root absorption, or evaporation is greater than root absorption, or drought prevents replenishment, the waterdrought prevents replenishment, the water“pressure” drops, causing cells to become flaccid, “pressure” drops, causing cells to become flaccid, causing stems and leaves to droop. causing stems and leaves to droop.

This is a temporary problem..

Wilting and Future Growth

Maintaining water Maintaining water turgorturgor (pressure) in a plant (pressure) in a plant is important. is important.

The drop in pressure causesThe drop in pressure causes stomatesstomates to close, to close, reducing water loss. The plant may be OK but reducing water loss. The plant may be OK but the long term effects on growth can be very the long term effects on growth can be very serious and take time to show up. serious and take time to show up.

What effects can you think of?

The Permanent Wilting PointThere is also a point in the process of wilting when the plant cell structure, which uses water to aid in cell rigidity, finally collapses irreversibly.

This point of no return is called the “permanent wilting point” or PWP.

You may add all the water you like to the plant system,but the cells will not recover, and the plant will stay wilted, and likely die.

We need to provide cuttings a film of water over their We need to provide cuttings a film of water over their leaves to reduce evaporation, and the loss of water from leaves to reduce evaporation, and the loss of water from the stems. Remember, there are no roots to replace the stems. Remember, there are no roots to replace the water! It must be adsorbed by the stem cut surface the water! It must be adsorbed by the stem cut surface and the leaves, and this is very inefficient!and the leaves, and this is very inefficient!

Root AnatomyThere are several distinct There are several distinct growth zones on a healthy growth zones on a healthy 2” root. The tip of the root 2” root. The tip of the root is primarily undifferentiatedis primarily undifferentiatedcells. The next 1/3 are cells cells. The next 1/3 are cells that are elongating and arethat are elongating and aredifferentiating. The upperdifferentiating. The upper1/3 are mature cells with 1/3 are mature cells with developing root hairs.developing root hairs.

Farther up the root, the Farther up the root, the root hairs die and the root hairs die and the epidermis becomes less epidermis becomes less permeable. Therefore, only permeable. Therefore, only the last inch of a growing the last inch of a growing root is involved in uptakeroot is involved in uptake

Root Hair AnatomyRoot Hair AnatomyRoot hairs work by the cell nucleus Root hairs work by the cell nucleus forming an extension of the cell forming an extension of the cell membrane, this forming the root hair. membrane, this forming the root hair.

There is only one nucleus, if the There is only one nucleus, if the membrane appendage is damaged, membrane appendage is damaged, the nucleus is usually killed and no the nucleus is usually killed and no new hair can be formed. The new hair can be formed. The epidermal cell usually dies. epidermal cell usually dies.

Over WateringOver WateringRoots need oxygen and water!

Roots are a membrane interface to the outside environment.Roots are a membrane interface to the outside environment.Like the leaves, gas exchange does take place in the roots. Like the leaves, gas exchange does take place in the roots. In this case, roots need oxygen to respire, and give off CO2.In this case, roots need oxygen to respire, and give off CO2.

If you provide water too often, If you provide water too often, the air spaces with the soilthe air spaces with the soilstay filled with water, and do stay filled with water, and do not allow gasses to flow throughnot allow gasses to flow throughthe soil. The plant roots actuallythe soil. The plant roots actuallysuffocate. Proper wateringsuffocate. Proper wateringflushes old air out and draws influshes old air out and draws innew air. new air. Can you determine why? Roots will not grow into oxygenRoots will not grow into oxygen--depleted soil.depleted soil.

Over-FertilizationAdding fertility in excess of Adding fertility in excess of the rate it is use by the plant the rate it is use by the plant causes build up, especially in causes build up, especially in containers with no weep holes.containers with no weep holes.

Excess fertilizer can cause bigExcess fertilizer can cause bigproblems for roots, and canproblems for roots, and canactually cause nutrient toxicityactually cause nutrient toxicityand deficiency. and deficiency.

Fertility levels must be checkedFertility levels must be checkedregularly, and soils flushed out at regularly, and soils flushed out at least twice a year. That, or pay least twice a year. That, or pay good money for a repotting! good money for a repotting!

Salt DamageSalts Actually Rob Water From Roots !

When fertilizerWhen fertilizer--laden soils dry out, the salts concentrateladen soils dry out, the salts concentrateand literally form crusts. To stay stable, salts need to and literally form crusts. To stay stable, salts need to bind with water. This water binds very tightly. If manybind with water. This water binds very tightly. If manysalt crystals form, and water is scarce, the salt formationsalt crystals form, and water is scarce, the salt formationprocess will actually cause a reverse gradient and pull process will actually cause a reverse gradient and pull water out of the outerwater out of the outerroot cells, root cells, dessicating dessicating and killing them. This and killing them. This is called is called salt burn,

Note salts below thewater evaporation zone!

The Economics Of Root FormationRegardless of whether you Regardless of whether you have a cutting or a salt have a cutting or a salt damaged plant, new roots damaged plant, new roots are what you need, fast!are what you need, fast!

Constant humidity, and plenty Constant humidity, and plenty of air spaces in the soil will of air spaces in the soil will encourage new root hairs to encourage new root hairs to form, and newform, and new meristemmeristem tissue to develop new root tissue to develop new root initials. You must concurrently reduce stress, initials. You must concurrently reduce stress, control temperature, maintain or improve light and yet control temperature, maintain or improve light and yet maintain low fertility and low water loss from leaves. maintain low fertility and low water loss from leaves.

This takes time, patience, consistent care and $$$!

New Installations Are Like Cuttings!

Providing water to plants in a new installations a tricky Providing water to plants in a new installations a tricky business. Watering must be only when needed, and never business. Watering must be only when needed, and never too late. Mulch, such as too late. Mulch, such as TillandsiaTillandsia ((spanishspanish moss), or bark moss), or bark chips can be added to reduce direct evaporation from chips can be added to reduce direct evaporation from soil. Plants can also be soil. Plants can also be moved into less direct moved into less direct light to reduce light to reduce evaporation until evaporation until roots reroots re--grow and grow and the plants settle in. the plants settle in.

Frequent site visitation is essential !

Overview Of Water Transport System In PlantsOverview Of Water Transport System In Plants

Know Your Plants!Each Plant Is Different

Trees Are Amazing!