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Water Regulati
on on Land
6.2
Allocation of
Organisms
???
Major Environmental
Challenges1.Massive losses of water due to evaporation.
2.Reduced access to water replacement.
In order to meet such Environmental Challenges…
Terrestrial Organisms regulate their internal water intake.
Howd
oorganisms theirintern
alwaterintak
e ?regulate
Internal WaterRegulation of Animals ()𝐖 𝐢𝐚=𝐖𝐝+𝐖 𝐟+𝐖𝐚−𝐖𝐞−𝐖𝐬
WATER SOURCES:Wd = DrinkingWf = FoodWa = Absorbed from the air
AVENUES OF WATER LOSS:We = water lost by EvaporationWs = Secretion / Excretion
𝐖𝐞𝐖𝐚
𝐖𝐝𝐖𝐟𝐖𝐬
(water acquisition through absorption)
(water acquisition through drinking &
food)
(water loss through evaporation)
(water loss through secretions)
Internal WaterRegulation of Plants ()𝐖 𝐢𝐩=𝐖 𝐫+𝐖𝐚−𝐖 𝐭−𝐖 𝐬WATER SOURCES:
Wr = Water taken by the rootsWa = Water absorbed from the
airAVENUES OF WATER LOSS:
Wt = Water lost by transpirationWs = Water lost by secretions
𝐖𝐬
𝐖𝐚
𝐖𝐭
𝐖𝐫
(water acquisition from moist air)
(water loss through transpiration) (water loss through
secretions such as nectar)
(water acquisition by roots)
Water Acquisiti
on by
Animals
Their need of acquiring water depends upon their environment.
Moist Environment
(forest)
Arid Environment
(desert)
Acquisition of Water in moist climates through…
Drinking
Food
Air
Acquisition of Water in dry climates through…
Metabolic Water
Air Moisture
Some desert animals acquire water in unusual ways.
(Lepidochora)
(Onymacris Unguicularis
)
Lepidochora
Collects moisture by
digging trenches on the face of sand dunes to condense and
concentrate fog.
Onymacris Unguicularis
Collects moisture by orienting its
abdomen upward.
Other MechanismWATER can also be gained via metabolism through oxidation of glucose:
C6H12O6 + 6O2 6CO2 + 6H2O
METABOLIC WATER refers to the water released during cellular respiration.
Kangaroo Rat
In every 100 g of barley that it eats, it gains 60 ml of water. 6 mL of it is the absorbed water that can be driven off by drying while the remaining 54 mL of water is released as the rat metabolizes the carbohydrates, fats, and proteins in the grain.
Water Acquisiti
on by
Plants
Plants acquire water through…
ROOTS
Plants in dry climates grow more roots than do plants in moist climates.
Moist Sites Dry Sites
In dry climates, plant roots tend to grow deeper in the soil and to constitute a greater proportion of biomass.
In deserts and semiarid grasslands, roots may account for up to 90% of total plant biomass while in coniferous forests, roots only constitute 25%.
Root Development
R. Coupland and R. Johnson (1965) compared the rooting characteristics of Artemesia frigida in the temperate grasslands of western Canada.
Soil moisture influences the extent of root development by Artemesia frigida.
OBSERVATION:Microclimate affects
root development.Deeper roots often
help plants from dry environment extract water from deep w/in soil.
Y.M. PARK studied two common grasses that grow in Japan
Digitaria adscendens Eleusine indica
Grows on coastal sand dunes
Does not grow on coastal sand dunes
Park’s Investigation on Root Growth
Park planted both grasses into tubes filled with sand from coastal dunes and kept them unwatered for 19 days.
He noticed that the root mass of Digitaria increased almost sevenfold over the 19 days of no watering, while the roots of Eleusine increased about threefold.
Leaf Water Potential
If a plant has lower root mass, its leaf water potential decreases.
If a plant has higher root mass, it maintains a higher leaf water potential.
Water Conservati
on by Plants & Animals
WaterproofingMany terrestrial
plants and animals cover themselves with a fairly waterproof “hide” impregnated with a variety of waterproofing waxes.
Neil Hadely & Thomas Shultz studied the waterproofing of 2 tiger beetles in different microclimates.
Cicendela oregona Cicendela obsoleta
(active in spring & fall)
(active in summer)
Waterproofing Cuticlesof Tiger Beetles
• The waterproofing cuticles of terrestrial insects are provided by hydrocarbons : Lipids & Waxes
“The lesser the hydrocarbon content, it is less waterproofed. The greater the hydrocarbon content, it is more waterproofed.”
Other Water-Conserving Mechanisms of Animals
Producing concentrated urine or feces with low water content
Condensing and reclaiming the water vapor in breath
Restricting activities to times and places that decrease water loss.
Plant Water Conservation
“How much water a plant can conserve depends in part on its leaf relative to its root area or length.”
Plants with more leaf surface per length of root lose more water.
Plants reduce leaf area by dropping of leaves.
Ocotillo
(produces leaves in times of rain)
(reduces leaf area to zero in times of
drought)
Temporary Wilting
It is a water-conserving mechanism that reduces leaf area exposed to solar radiation by 55% and leaf temperature up to 4⁰ to 5⁰C.
It decreases the rate of transpiration by 30% to 50%, which is a substantial water savings.
After 8 minutes, wilting reduces the surface area.
Other Plant Adaptations that Conserve Water
• Plants with thick leaves• Few stomata on leaves• Structures on the stomata that blocks
the movement of water• Dormancy during times when moisture
unavailable• Alternative water-conserving for
photosynthesis.
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