BIOL 4120: Principles of Ecology
Lecture 2: Adaptation to
Physical Environment: Water
and Nutrients
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Topics (Chapter 2):
2.1 Global water cycling
2.2 Water has many properties favorable to life
2.3 Many inorganic nutrients are dissolved in
water
2.4 Plants obtain water and nutrients from soil
2.5 Maintain salt and water balance by plants and
animals
2.1 Global Hydrologic (water) cycle
between Earth and atmosphere


Water is essential for life
(75-95% weight of living
cell)
Over 75% of the Earth’s
surface is covered by
water
• Oceans contain 97%.
• Polar ice caps and
glaciers contain 2%.
• Freshwater in lakes,
streams, and ground
water make up less
than 1%.
(Saltwater and fresh water)
Water Cycles between Earth and
the Atmosphere


The water (or hydrologic) cycle is
the process by which water travels in
a sequence from the air to Earth and
returns to the atmosphere
Solar radiation is the driving force
behind the water cycle because it
provides energy for the evaporation
of water
The Hydrologic Cycle







Distribution of water is not static (processes)
Precipitation
(PPT)
Interception
Infiltration
Groundwater
recharge
Runoff
Evaporation
(E)
Transpiration
(T)
Global water budget
Land
Pools (10^3 km3):
Glaciers: 29,000
Groundwater:4,000
Lake: 229
Soil: 67
Fluxes (km3/yr):
PPT: 111,000
ET: 71,000
River flow:40,000
Ocean
Pools: (10^3 km3)
Ocean:1.37*10^6
Fluxes: (km3/yr)
PPT:385,000
ET: 425,000
2.2 Properties of water that favorable to
life
Basic Structure
1. Covalent bonding of 2H + O atoms
2. Polar-covalent bond
3. Inter-molecule attraction
4. H-bonds among water moleculars
Physical and chemical properties
Thermal properties of water: High specific heat
capacity
1.Specific Heat: 1.0 (also called Heat Capacity)
• calories required to raise 1 g H2O 1oC high
• (e.g. from 10 to 11oC) (Stable T in lakes
and organisms)
2. Latent heat: energy released or absorbed in the
transformation of water from one state to another.
1 calorie to raise 1oC; 536 calories to change 100oC
water to vapor; 86 calories ice to 1oC water


3. Peculiar density-temperature relationship
Density increases as T decreases (when T> 4oC),
then decrease to 0oC, freezing (ice), float.

Cohesion
Due to the hydrogen bonding, water
molecules tend to stick firmly to each
other, resisting external forces that would
break the bonds (drop of water,
transpiration).

Surface tension
Strong attraction within
the water body and
weaker attraction in the
surface caused that
molecules at the surface
are drawn downward.



High viscosity
Viscosity: measures the force necessary to
separate the molecules and allow passage of an
object through liquid.
Frictional resistance is 100 times greater than air.
Water is 860 times denser than air.
• Organisms in water have similar density to
water, the neutral buoyancy helps against the
force of gravity, thus require less investment
in structure material such as skeletons
• Organisms in deep water need to adapt to the
high pressure (20 to 1000 atm).
2.3 Many inorganic nutrients are
dissolved in water
Solution: a homogeneous liquid
with 2 or more substances mixed.
Solvent: dissolving agent
Solute: substance that is dissolved
Aqueous solution: water as
solvent
Ions: Compounds of electrically
charged atoms
Cations: positive
Anions: negative
Practical salinity units (PSU,
o/oo): grams of salt per
kilogram of water.
Ocean: 35 unit, Fresh water:
0.065-0.30 unit)
Hydrogen ions in ecological systems
Hydrogen ions are very active: 1) affect enzyme
activities, and thus influence life processes; 2)
dissolve minerals from rocks and soils.
Acidity: the abundance of hydrogen ions (H+) in
solution.
Alkalinity: abundance of hydroxyl ions (OH-) in
solution
Acidity in water is related to carbon dioxide (CO2).
Forms of carbon in water

Carbon-bicarbonate equilibrium
• Carbon dioxide:
CO2
• Carbonic acid:
H2CO3
• Bicarbonate:
HCO3• Carbonate:
CO32-
CO2 + H2O H2CO3 HCO3- + H+ CO32- + 2H+

Measurement: pH =-log([H+])
(value between 1-14)


Pure water: 7 Acidic: <7 Alkaline: >7
Ocean water tends to be slightly
alkaline with a pH range of 7.5-8.4
2.4 Plants obtain water and
nutrients from soil

Plants and animals need water and
nutrients to growth and reproduce.
Plants acquire the inorganic
nutrients as ions dissolved in water
N: ammonium (NH4+), nitrate (NO3-)
3 P: phosphate ions (PO4 )
 K: K+
 Na: Na +
 Ca: Ca2+
The availability in soil is determined by
their chemical forms in soil,
temperature, acidity, and presence
of other ions.

2.4.1 Ion exchange capacity is
important to soil fertility
Soil soluble nutrients are charged
particles, ions.
Cations: positively charged (Ca2+, Mg2+,
NH4+)
Anions: negatively charged (NO3–, PO34–)
Ions are attached to soil particles, so
they do not leach out of the soil.
Ion exchange capacity: total number of
charged sites on soil particles in a
standard volume of soil.
Soils have an excess of negative
charged sites


Cationic exchange
dominant (colloids)
Cation exchange
capacity (CEC): total # of
negatively charged sites, located on
the leading edges of clay particles
and Soil Organic Matter.

Concentration and
affinity
Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+
> Na+
Process of cation exchange in soils
In soils with high Mg++ or Ca++, K+ is lacking, why?
2.4.2 Soil properties and water-holding
capacity

Texture
• Variation in size and
shape of soil particles
 Gravel (NOT)
• >2mm



Sand
• 0.05mm to
2mm
Silt
• 0.002mm to
0.05mm
Clay
• <0.002mm
Soil texture is percentage of sand, silt
and clay. (Texture chart)
Sand: 58%
Clay: 14%
Silt: 28%
Water holding capacity is an essential feature of
soils



Soil can become saturated if
all pores filled
All water is hold by soil
particulars, at field capacity
(FC)
Capillary water is usually
present
• Extractable by plants

Wilting point (WP)
• Plant no long extract water
Available water capacity (AWC)

All affected by soil texture
• Sand

Lower capacity
• Clays

Higher capacity
Water content at different soils
2.4.3 Water moves from soil to plant to atmosphere
Water potential


Water moving between soil and plants
flows down a water potential gradient.
Water potential ( ) is the capacity of
water to do work, potential energy of
water relative to pure water.
• Pure Water  = 0.
 in nature generally negative.
 due to dissolved
  solute measures the reduction in
substances.

Water potential of compartment of soil-plant-atmosphere
•

w
=

p
+

o
+

m
• Hydrostatic pressure or physical pressure
(cell wall).
• Osmotic potential: tendency to attract water
molecule from areas of low concentrations
to high. This is the major component of total
leaf and root water potentials.
• Matric potential: tendency to adhere to
surfaces, such as container walls. Clay soils
have high matric potentials.
Water moves from soil to plant to atmosphere
The cohesion-tension
theory explains the
movement of water from
the roots to a leaf of a
plant.
1. Through Xylem
2. No metabolic energy
required
3. Depends on physicalchemical properties of
water, driven by water
potential.
Stick to each other and
adhere to cell wall.
BIOL 4120: Principles of Ecology
Lecture 2: Adaptation to
Physical Environment: Water
and Nutrients
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Recap:
Water properties
Many inorganic nutrients are dissolved in water
Nutrients, pH
Plants obtain water and nutrients from soil
Soil and nutrient (CEC)
Soil properties and water (water holding
capacity)
Water movement from roots to plants to air
2.5 Maintenance of salt and water
balance


To maintain proper amount of water and dissolved substances in
their bodies, organisms must balance losses with intake.
When organisms take in water with solute concentration differs
from that of their bodies, they must either acquire more solutes to
make up the deficit or get rid of excess solutes:




Uptake of water with solutes
Evaporation from surface of terrestrial organisms into
atmosphere
Solutes left behind, high salt concentration
Solutes determine osmotic potential of body fluids, the
mechanisms that organisms use to maintain a proper salt
balance are referred to as osmoregulation.
2.5.1 Management of salt balance
by plants
Transpiration – water uptake – dissolved salts along water will
get into roots
When salts concentrations in soil water are high, plants pump
excess salts back into soil by active transport across their root
surface, function as plant’s “kidneys”.
One example:
Mangroves on
coastal mudflats
Salt glands on
the leaf surface
2.5.2 Water and salt balance in
terrestrial animals

Terrestrial
• Input
 Drinking
 Eating
 Produced by metabolism (respiration)
• Output – Need to control in extreme environments
 Urine
• Concentrated to avoid water loss (Kidneys). Human: 4
times high than in blood; Kangaroo rat: 14 times
 Feces
 Evaporation
• No sweat glands in some mammals;
• “salt glands” in birds and reptiles
 Breathing
What happens to ungulates in a hot
dry climate like Africa?
No pants, no
sweating to save
water, store heat in
body (T up to 46oC
at daytime, release
heat at night 36oC)
Countcurrent heat
exchange to lower
head T
Eat at nighttime,
more water in plants
Respiration to
produce water
Oryx
2.5.3 Water and salt balance in
aquatic animals
• Freshwater (hyper-osmotic, high salt in
body)


Prevent excess uptake of water
Remove excess water
• Large amounts of very dilute urine
• Retain salt in special cells (gills, kidneys)
• Saltwater (hypo-osmotic, low salt in body)

If salt concentration is higher than in body,
dehydrate
• Drinking a lot to gain water
• Some sharks: retain urea in the bloodstream
(balance body surface water loss)
• Ion pumps, gill (fish)
• Kidneys (eliminate salts, marine mammals)
• Salt secreting glands in birds
The End
Proportions of the forms
of CO2 in Relation to pH
Free
Bicarbonate
Carbonate
pH
CO2
HCO3–
4
0.996
0.004
1.26 x 10-9
5
0.962
0.038
1.20 x 10-7
6
0.725
0.275
0.91 x 10-5
7
0.208
0.792
2.60 x 10-4
8
0.025
0.972
3.20 x 10-3
9
10
0.003
0.000
0.966
0.757
0.031
0.243
CO3=
Recap:
Water properties
Many inorganic nutrients are dissolved in water
Nutrients, pH
Plants obtain water and nutrients from soil
Soil and nutrient (CEC)
Soil properties and water (water holding
capacity)
Water movement from roots to plants to air
Recap:
Physical environment: water and nutrient
Water properties
Inorganic nutrients need to be dissolved in
water, Nutrients uptake from soil
Ion exchange capacity is a measure of soil
fertility
Soil texture and water holding capacity
Water movement from soil to plant to
atmosphere