Chapter 5 Water relations Life on earth linked closely with water

Metabolic rate and salt concentration in body fluids Ionic concentrations affect shape of enzymes (performance) Loss of enzyme function = ? Water uptake, loss, active transport of water

Water movement = high concentration to low concentration Or, low salt concentration to high salt concentration

Measuring Water Gradients In Terrestrial Environments Water Vapor Pressure: Amount of atmospheric pressure due to water molecules Vapor density = g water / m3 air Relative Humidity 100 x Actual vapor density / Saturation Water Content

Water content of air Water vapor Relative humidity = Changes with T water vapor density saturation water vapor density Changes with T warm air can hold more water

Fig 6.2

So what? At saturation vapor pressure, water precipitates from air as fast as it is evaporated

The effect? Greater difference between saturation vapor pressure and actual vapor pressure: = more rapidly water will evaporate This term = vapor pressure deficit

Fig 6.3

Terrestrial environments have high variation in water: Temporal variation mainly seasonal Solar warming and evaporation

Terrestrial environments have high variation in water: Hadley cells Tropical rainforests tend to be equatorial Deserts tend to be ~ 30˚

Spatial variation due to: Oceans, mountains, prevailing winds Environmental T Topographic position + draining Soil type = water retention by roots

Terrestrial organisms: Regulate water by balancing acquisition with losses Consumption, root uptake Evaporation, excretion, transpiration

Warm/hot terrestrial environ: Many species evaporate water

Aquatic environments Water availability based on water potential gradient Body fluid to environment

Water moves from high to low potential Water concentration gradient Water into roots - soil particles Up stem = xylem tube Evaporates out of leaves (vpd) Fig 6.5

Freshwater environments: Environment has higher water potential (lower salt concentration) Freshwater organisms are hyper-osmotic Organisms tend to gain water and lose salts

Freshwater environments: Adaptations? Use energy to take-up salts Excrete large amounts dilute urine

Freshwater fish + inverts Hyperosmotic => tend to gain water, lose salts In gills, cells absorb NaCl Kidneys produce much dilute urine

Energy Expended Fig 6.28

Marine environments: Environment has lower water potential (higher salt concentration) Organisms tend to lose water and gain salts = hypo-osmotic Adaptations? Drink much, use energy to excrete salts, excrete little and concentrated urine

Marine fish + inverts Hypo-osmotic = lose water, gain salts Drink seawater Gill cells secrete NaCl Kidneys produce concentrated urine

Isosmotic marine organisms: Same concentration inside as outside Sharks, many marine invert’s (e.g., crabs, shrimps)

Fig 6.4

Case history: desert beetle p. 133 Water budget Water intake = 50 mg/g body mass per day 40 mg from fog 1.7 mg from food 8.4 mg from metabolic water

Fig 6.8

Tiger beetles in Arizona One species adjacent to streams Another in dry grasslands How much water is lost through cuticle by each? Lab chamber (30 C , dry)

Fig 6.15 Cuticle is more waterproof

less = more lipids + wax

Fig 6.14

Fig 6.25

Cicadas can evaporate water to cool their body In lab chamber - T = 45.5 C Body T = 42.5 C When relative humidity = 100 % Body T = 45.5 C When relative humidity = 0 % Body T = 41.5 C

Fig 6.22

Root growth and water Grassland plants in western Canada Fringed sage Moist microclimate = Lower root biomass Higher aboveground biomass

Fig 6.11 - silver sage

The End