Principles of terrestrial ecosystem ecology.pdf

example, show that some plants derive most
of their water from fog, whereas others use
soil water or ground water. These measurements
also differentiate water derived from
winter vs. summer precipitation (Dawson
1993). Similarly, D:H ratios of stream water
Figure 4.10. Isotopic signature
of water from various
sources. By sampling the
water in the xylem of plants,
one can determine the
main water supply used by
a plant. (Redrawn with permission
from Academic
Press; Dawson 1993.)
Day ψ day
Transpiration
-90
Precipitation
Fog
Summer
Winter
Fossil
water
Air
Water Movements Within Ecosystems 85
Soil water and
runoff
Ground
water
ψ night
-30
-4.2 Leaves -1.2
Surface
-4.0 soil -4.0
-4.1 Roots -1.2
-1.0
Figure 4.11. Patterns of soil water potential and
water movement in arid environments during the
day and at night. During the day, water moves from
soils (especially deep soils) to the atmosphere in
Deep
soil
identify the relative contributions of soil
water from recent precipitation events vs.
ground water. Oxygen isotope ratios in
water show patterns of variation similar to
those of hydrogen.
-1.0
?
Night
Xylem water
Hydraulic lift
response to the strong water potential gradient from
the plant to the atmosphere. At night, water moves
from wet soils at depth to dry surface soils through
the root system, the process of hydraulic lift.