Transcript Water and Salt Balance in Aquatic Environments

Chapter 5
Water Relations
鄭先祐(Ayo)
靜宜大學 生態學系
Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/
Email add: [email protected]
Outline









Water Availability
Water Content of Air
Water Movement in Aquatic Environments
Water Movement Between Soils and Plants
Water Regulation on Land
Water Acquisition by Animals
Water Acquisition by Plants
Water Conservation by Plants and Animals
Water and Salt Balance in Aquatic Environments
2
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.

Must consider an organism’s microclimate (微氣候)
in order to understand its water relations.
3
Water Content of Air

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.
Evaporative coolers work best in dry climates.
於乾燥的氣候，蒸發的冷卻效果最好。

4
Water Content of Air

Relative Humidity: (相對溼度)
Water Vapor Density
Saturation Water Vapor Density


(x 100)
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.

Changes with temperature.
5
Water Content of Air

Total Atmospheric Pressure (大氣壓)


Water Vapor Pressure (水氣壓)


Partial pressure due to water vapor.
Saturation Water Vapor Pressure (飽和水氣壓)


Pressure exerted by all gases in the air.
Pressure exerted by water vapor in air saturated by
water.
Vapor Pressure Deficit (水氣壓赤字)

Difference between WVP and SWVP at a particular
temperature.
6
Evaporative Water Loss
7
Water Movement in Aquatic
Environments (水域環境)

Water moves down concentration gradient.


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.
8
Water Movement in Aquatic
Environments

If two environments differ in water or salt
concentrations, substances will tend to move
down their concentration gradients.
Diffusion (擴散)
 Osmosis (滲透): Diffusion through a semipermeable
membrane.

9
Water Movement in Aquatic
Environment



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.
Hyper-osmotic(高): Body fluids are at a lower
concentration than the external environment.
10
11
Water Movement Between Soils
and Plants


Water moving between soil and plants flows
down a water potential gradient.
Water potential () is the capacity to perform
work.
Dependent on free energy content.
 Pure Water  = 0.

 in nature generally negative.
 solute measures the reduction in  due to dissolved
substances.

12
13
Water Movement Between Soils
and Plants

plant = solute + matric + pressure
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.
 As long as plant > soil, water flows from the soil
to the plant.

14
Water Regulation on Land

Terrestrial organisms face (2) major challenges:
Evaporative loss to environment.
 Reduced access to replacement water.

15
Water Regulation on Land Animals

Wia= Wd + Wf + Wa - We - Ws

Wia= Animal’s internal water
Wd = Drinking
Wf = Food
Wa = Absorbed by air
We = Evaporation
Ws = Secretion / Excretion





16
Water Regulation on Land Animals
17
Water Regulation on Land Plants

Wip= Wr + Wa - Wt - Ws

Wip= Plant’s internal water
Wr =Roots
Wa = Air
Wt = Transpiration
Ws = Secretions




18
Water Regulation on Land - Plants
19
Water Acquisition by Animals

Most terrestrial animals satisfy their water needs
via eating and drinking.
Can also be gained via metabolism through
oxidation of glucose:
 C6H12O6 + 6O2  6CO2 + 6H2O
 Metabolic water refers to the water released during
cellular respiration.

20
Water Acquisition by Plants

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.
 Park found supportive evidence via studies
conducted on common Japanese grasses, Digitaria
adscendens and Eleusine indica.

21
Water Conservation by Plants and
Animals








Many terrestrial organisms equipped with
waterproof (不透水) outer covering.
Concentrated urine / feces.
Condensing water vapor in breath.
Behavioral modifications to avoid stress times.
Drop leaves in response to drought.
Thick leaves
Few stomata
Periodic dormancy
22
Dissimilar Organisms with
Similar Approaches to Desert Life

Camels

Can withstand water loss up to 20%.
Face into sun to reduce exposure.
 Thick hair: Increased body temperature lowers heat
gradient.


Saguaro Cactus
Trunk / arms act as water storage organs.
 Dense network of shallow roots.
 Reduces evaporative loss.

23
24
Two Arthropods with Opposite
Approaches to Desert Life

Scorpions
Slow down, conserve, and stay out of sun.
 Long-lived
 Low metabolic rates


Cicadas (Diceroprocta apache)
Active on hottest days.
 Perch on branch tips (cooler microclimates).
 Reduce abdomen temp by feeding on xylem fluid of
pinyon pine trees.

25
Water and Salt Balance in Aquatic
Environments

Marine Fish and Invertebrates
Isomotic organisms do not have to expend energy
overcoming osmotic gradient.
 Sharks, skates, rays - Elevate blood solute
concentrations hyperosmotic to seawater.
 Slowly gain water osmotically.
 Marine bony fish are strongly hypo-osmotic, thus need
to drink seawater for salt influx.

26
Osmoregulation by Marine Organisms
27
Water and Salt Balance in Aquatic
Environments


Freshwater Fish and Invertebrates
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.
28
Osmoregulation by Freshwater Organisms
29
Applications & Tools




Stable isotope analysis
Stable isotopes of hydrogen include 1H and 2H,
which is generally designated as D, an
abbreviation of deuterium.
Stable isotopes of carbon, for example, include
13C and 12C.
to study water uptake by plants
30
Review









Water Availability
Water Content of Air
Water Movement in Aquatic Environments
Water Movement Between Soils and Plants
Water Regulation on Land
Water Acquisition by Animals
Water Acquisition by Plants
Water Conservation by Plants and Animals
Water and Salt Balance in Aquatic Environments
31
32