Water Relations Chapter 5 鄭先祐 (Ayo) 靜宜大學 生態學系 Ayo 台南站： add:

2 Outline Water Availability Water Availability Water Content of Air Water Content of Air Water Movement in Aquatic Environments Water Movement in Aquatic Environments Water Movement Between Soils and Plants Water Movement Between Soils and Plants Water Regulation on Land Water Regulation on Land Water Acquisition by Animals Water Acquisition by Animals Water Acquisition by Plants Water Acquisition by Plants Water Conservation by Plants and Animals Water Conservation by Plants and Animals Water and Salt Balance in Aquatic Environments Water and Salt Balance in Aquatic Environments

3 Water Availability The tendency of water to move down concentration gradients, and the magnitude of those gradients, determine whether an organism tends to lose or gain water from its environment. The tendency of water to move down concentration gradients, and the magnitude of those gradients, determine whether an organism tends to lose or gain water from its environment. Must consider an organism ’ s microclimate ( 微氣候 ) in order to understand its water relations. Must consider an organism ’ s microclimate ( 微氣候 ) in order to understand its water relations.

4 Water Content of Air Evaporation accounts for much of water lost by terrestrial organisms. Evaporation accounts for much of water lost by terrestrial organisms. As water vapor in the air increases, the water concentration gradient from organisms to air is reduced, thus evaporative loss is decreased. As water vapor in the air increases, the water concentration gradient from organisms to air is reduced, thus evaporative loss is decreased. Evaporative coolers work best in dry climates. Evaporative coolers work best in dry climates.於乾燥的氣候，蒸發的冷卻效果最好。

5 Water Content of Air Relative Humidity: ( 相對溼度 ) Relative Humidity: ( 相對溼度 ) Water Vapor Density Water Vapor Density Saturation Water Vapor Density (x 100) Water vapor density is measured as the water vapor per unit volume of air. Water vapor density is measured as the water vapor per unit volume of air. Saturation water vapor density is measured as the quantity of water vapor air can potentially hold. Saturation water vapor density is measured as the quantity of water vapor air can potentially hold. Changes with temperature. Changes with temperature.

6 Water Content of Air Total Atmospheric Pressure ( 大氣壓 ) Total Atmospheric Pressure ( 大氣壓 ) Pressure exerted by all gases in the air. Pressure exerted by all gases in the air. Water Vapor Pressure ( 水氣壓 ) Water Vapor Pressure ( 水氣壓 ) Partial pressure due to water vapor. Partial pressure due to water vapor. Saturation Water Vapor Pressure ( 飽和水氣壓 ) Saturation Water Vapor Pressure ( 飽和水氣壓 ) Pressure exerted by water vapor in air saturated by water. Pressure exerted by water vapor in air saturated by water. Vapor Pressure Deficit ( 水氣壓赤字 ) Vapor Pressure Deficit ( 水氣壓赤字 ) Difference between WVP and SWVP at a particular temperature. Difference between WVP and SWVP at a particular temperature.

7 Evaporative Water Loss

8 Water Movement in Aquatic Environments ( 水域環境 ) Water moves down concentration gradient. Water moves down concentration gradient. Water is more concentrated in freshwater ( 淡水 ) environments than in the oceans. Water is more concentrated in freshwater ( 淡水 ) environments than in the oceans. Aquatic organisms can be viewed as an aqueous solution bounded by a selectively permeable membrane floating in an another aqueous solution. Aquatic organisms can be viewed as an aqueous solution bounded by a selectively permeable membrane floating in an another aqueous solution.

9 Water Movement in Aquatic Environments If two environments differ in water or salt concentrations, substances will tend to move down their concentration gradients. If two environments differ in water or salt concentrations, substances will tend to move down their concentration gradients. Diffusion ( 擴散 ) Diffusion ( 擴散 ) Osmosis ( 滲透 ): Diffusion through a semipermeable membrane. Osmosis ( 滲透 ): Diffusion through a semipermeable membrane.

10 Water Movement in Aquatic Environment Isomotic ( 同等 ): Body fluids and external fluid are at the same concentration. Isomotic ( 同等 ): Body fluids and external fluid are at the same concentration. Hypo-osmotic( 低 ): Body fluids are at a higher concentration than the external environment. Hypo-osmotic( 低 ): Body fluids are at a higher concentration than the external environment. Hyper-osmotic( 高 ): Body fluids are at a lower concentration than the external environment. Hyper-osmotic( 高 ): Body fluids are at a lower concentration than the external environment.

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12 Water Movement Between Soils and Plants Water moving between soil and plants flows down a water potential gradient. Water moving between soil and plants flows down a water potential gradient. Water potential (  ) is the capacity to perform work. Water potential (  ) is the capacity to perform work. Dependent on free energy content. Dependent on free energy content. Pure Water  = 0. Pure Water  = 0.  in nature generally negative.  in nature generally negative.  solute measures the reduction in  due to dissolved substances.  solute measures the reduction in  due to dissolved substances.

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14 Water Movement Between Soils and Plants  plant =  solute +  matric +  pressure  plant =  solute +  matric +  pressure Matric Forces: Water ’ s tendency to adhere to container walls. Matric Forces: Water ’ s tendency to adhere to container walls.  pressure is the reduction in water potential due to negative pressure created by water evaporating from leaves.  pressure is the reduction in water potential due to negative pressure created by water evaporating from leaves. As long as  plant >  soil, water flows from the soil to the plant. As long as  plant >  soil, water flows from the soil to the plant.

15 Water Regulation on Land Terrestrial organisms face (2) major challenges: Terrestrial organisms face (2) major challenges: Evaporative loss to environment. Evaporative loss to environment. Reduced access to replacement water. Reduced access to replacement water.

16 Water Regulation on Land - Animals W ia = W d + W f + W a - W e - W s W ia = W d + W f + W a - W e - W s W ia = Animal ’ s internal water W ia = Animal ’ s internal water W d = Drinking W d = Drinking W f = Food W f = Food W a = Absorbed by air W a = Absorbed by air W e = Evaporation W e = Evaporation W s = Secretion / Excretion W s = Secretion / Excretion

17 Water Regulation on Land - Animals

18 Water Regulation on Land - Plants W ip = W r + W a - W t - W s W ip = W r + W a - W t - W s W ip = Plant ’ s internal water W ip = Plant ’ s internal water W r =Roots W r =Roots W a = Air W a = Air W t = Transpiration W t = Transpiration W s = Secretions W s = Secretions

19 Water Regulation on Land - Plants

20 Water Acquisition by Animals Most terrestrial animals satisfy their water needs via eating and drinking. Most terrestrial animals satisfy their water needs via eating and drinking. Can also be gained via metabolism through oxidation of glucose: Can also be gained via metabolism through oxidation of glucose: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O Metabolic water refers to the water released during cellular respiration. Metabolic water refers to the water released during cellular respiration.

21 Water Acquisition by Plants Extent of plant root development often reflects differences in water availability. Extent of plant root development often reflects differences in water availability. Deeper roots often help plants in dry environments extract water from deep within the soil profile. Deeper roots often help plants in dry environments extract water from deep within the soil profile. Park found supportive evidence via studies conducted on common Japanese grasses, Digitaria adscendens and Eleusine indica. Park found supportive evidence via studies conducted on common Japanese grasses, Digitaria adscendens and Eleusine indica.

22 Water Conservation by Plants and Animals Many terrestrial organisms equipped with waterproof ( 不透水 ) outer covering. Many terrestrial organisms equipped with waterproof ( 不透水 ) outer covering. Concentrated urine / feces. Concentrated urine / feces. Condensing water vapor in breath. Condensing water vapor in breath. Behavioral modifications to avoid stress times. Behavioral modifications to avoid stress times. Drop leaves in response to drought. Drop leaves in response to drought. Thick leaves Thick leaves Few stomata Few stomata Periodic dormancy Periodic dormancy

23 Dissimilar Organisms with Similar Approaches to Desert Life Camels Camels 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 lowers heat gradient. Thick hair: Increased body temperature lowers heat gradient. Saguaro Cactus Saguaro 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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25 Two Arthropods with Opposite Approaches to Desert Life Scorpions Scorpions Slow down, conserve, and stay out of sun. Slow down, conserve, and stay out of sun. Long-lived Long-lived Low metabolic rates Low metabolic rates Cicadas (Diceroprocta apache) Cicadas (Diceroprocta apache) Active on hottest days. Active on hottest days. Perch on branch tips (cooler microclimates). Perch on branch tips (cooler microclimates). Reduce abdomen temp by feeding on xylem fluid of pinyon pine trees. Reduce abdomen temp by feeding on xylem fluid of pinyon pine trees.

26 Water and Salt Balance in Aquatic Environments Marine Fish and Invertebrates Marine Fish and Invertebrates Isomotic organisms do not have to expend energy overcoming osmotic gradient. Isomotic organisms do not have to expend energy overcoming osmotic gradient. Sharks, skates, rays - Elevate blood solute concentrations hyperosmotic to seawater. Sharks, skates, rays - Elevate blood solute concentrations hyperosmotic to seawater. Slowly gain water osmotically. Slowly gain water osmotically. Marine bony fish are strongly hypo-osmotic, thus need to drink seawater for salt influx. Marine bony fish are strongly hypo-osmotic, thus need to drink seawater for salt influx.

27 Osmoregulation by Marine Organisms

28 Water and Salt Balance in Aquatic Environments Freshwater Fish and Invertebrates Freshwater Fish and Invertebrates Hyper-osmotic organisms that excrete excess internal water via large amounts of dilute urine. Hyper-osmotic organisms that excrete excess internal water via large amounts of dilute urine. Replace salts by absorbing sodium and chloride at base of gill filaments and by ingesting food. Replace salts by absorbing sodium and chloride at base of gill filaments and by ingesting food.

29 Osmoregulation by Freshwater Organisms

30 Applications & Tools Stable isotope analysis Stable isotope analysis Stable isotopes of hydrogen include 1 H and 2 H, which is generally designated as D, an abbreviation of deuterium. Stable isotopes of hydrogen include 1 H and 2 H, which is generally designated as D, an abbreviation of deuterium. Stable isotopes of carbon, for example, include 13 C and 12 C. Stable isotopes of carbon, for example, include 13 C and 12 C. to study water uptake by plants to study water uptake by plants

31 Review Water Availability Water Availability Water Content of Air Water Content of Air Water Movement in Aquatic Environments Water Movement in Aquatic Environments Water Movement Between Soils and Plants Water Movement Between Soils and Plants Water Regulation on Land Water Regulation on Land Water Acquisition by Animals Water Acquisition by Animals Water Acquisition by Plants Water Acquisition by Plants Water Conservation by Plants and Animals Water Conservation by Plants and Animals Water and Salt Balance in Aquatic Environments Water and Salt Balance in Aquatic Environments

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