Water Balance in Terrestrial Plants. Water Regulation on Land - Plants. W ip = W r + W a - W t - W s W ip = Plantâ€™s internal water W r =Roots W a = Air W t = Transpiration W s = Secretions. Water Regulation on Land - Plants. Water Balance in Terrestrial Plants.
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Wip= Wr + Wa - Wt - Ws
Water flows along energy gradients.
Gravity—water flows downhill. The associated energy is gravitational potential.
Pressure—from an area of higher pressure, to lower. The associated energy is pressure (or turgor) potential.
Osmotic potential—water flows from a region of high concentration (low solute concentration) to a region of low concentration (high solute concentration).
Matric potential—energy associated with attractive forces on surfaces of large molecules inside cells or on surfaces of soil particles.
Salt glands exuding salt droplets
California poppies and other ephemerals from the Mojave Desert of the American Southwest
Blue Phacelia from the Sonoran and Mojave Deserts
Enhanced cuticle, a waxy covering, which prevents water loss.
Leaves of plants like the Jojoba and Compass Plant face N-S, minimizing exposure to most intense sunlight.
Spines and hairs discourage herbivores and help shade plant.
Aloes in Namib Desert
Lichens on rock in Big Bend Nat’l Park
Note countersunk guard cells and thick cuticle
CO2 converted to a 3 C compound
Occurs in palisade mesophyll cells
CO2 converted to a 4C compound in mesophyll cell
RUBISCO operates in bundle sheath cell where CO2 conc. is high.
C4 plants have spatial separation of the C4 and C3 pathways of carbon fixation.
C4 pathway used at night when water loss is low
Stomata completely closed during day
Crassulacean acid metabolism plants have a temporal separation of C4 and C3 pathways of carbon fixation.
Take up CO2
Produce crassulacean acid
stores CO2 as a C4 acid
Use stored CO2 for standard C3 photosynthesisCrassulacean acid metabolism (CAM)Light and dark reactions of photosynthesis are uncoupled so stomates are closed during the day
Air spaces in a water lily stem
HETEROPHYLLY Condition where the same organ has a change in form.
The submerged aquatic leaf is simple, (upper diagram) and only three cells thick, while the floating leaf (lower diagram) contains numerous intercellular airspaces and has a columnar mesophyll arrangement.