Sept. 2 and 11, 1997
Adaptations to Aquatic Environments
Aquatic plants evolved from terrestrial plants. Like whales and othermarine mammals, aquatic plants evolved from land back to aquatic habitats.Aquatic plants modified terrestrial features to withstand emerged, submerged,or floating conditions.
Types of Challenges
Emergent Submerged Floating
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Aeration of Roots :don't have thisproblem,
Solutions: theiradventituous roots
1) formation of aerenchyma: stayabove the aerobic
large, open spaces between cells, zone to collect oxygen
important for carrying oxygen
down to the root zone to oxidize/
aerate nutrients
2) formation of prop roots, pores, :proproots most lenticels: lets more oxygen in common on red mangroves
black mangroves use
pnuematophores
3) anaerobic respiration: plant will
form ethylene-then will form more
aerenchyma, adventituous roots,
and plant will elongate, form fatty
acids (ethylene is a common gas
in swamps due to decay)
Sexual Reproduction ________________________________________________________________
-sexual reproduction is rare: the Vallisneria:coiled peduncle
most common forms: (female)will straighten out so
1) fragmentation: most common form, the stigma will reach above the
pieces break off and float away to watersurface. The spathe(male)
again become embedding in the willalso straighten out so its
substrate tepalsfloat on the surface. Its
2) rhizome: underground stems, threeleaves and anthers form a
part of root strays and comes back sailboat.The spathe floats along
up to surface to start another plant untilhopefully its anthers touch
3) stolon: aboveground stems, astigma floating at the surface.
this is the same as the rhizome but Ceratophyllum:uses strategy of
root is aboveground hydrophyily:male releases pollen
intothe water where it floats
alonguntil it sinks again, hopefully
landing on a female plant.
AChinese lotus can lay dormant
over1,000 years, some other
fragmentsand seeds do this too.
Seed Germination ____________________________________________________________________________
Strategies:
1) Timing of seed production
in the non-flood season either
by delated or accelerated
flowering.
2) The production of bouyant
seeds that float on high
unflooded ground
3) germination of seeds while
the fruit is still attached to the
tree (vivpary).
Photosynthesis (Gas Exchange) ________________________________________________________________
Problems:
-As water gets deeper, Algaeblooms block most
wavelengths of light get shorter ofthe light and nutrients from
until gone. The red and blue wave- otherplants
lenghts are lost, only the greens left
which are not very good for
phototsynethsis.
Solutions:
1) Wetland plants use C4
biochemical pathway of
photosynthesis instead of C3.
-C4 provides a possible pathway
for recycling CO2 from cell
respiration
-plants using C4 have low
photorespiration rates and the
ability to use even the most
intense sunlight efficiently.
-C4 plants more efficient than
C3 plants in rate of carbon
fixation and amount of water
used per unit carbon fixed.
Salinity ___________________________________________________________________________________
Solutions:
1) barriers prevent or control
the entry of salts
-root and leaf cell memebrane
act like ultrafilters
2) organs specialized to excrete
salts
-selectively remove certain ions
from the vascular tissus of the leaf
Aeration of Roots -
Oxygen is transmitted from the leaves to the roots and rhizomes by lacunae(air spaces forming channels in leaves, stems, and roots). Lacunae alsohave a structural role. Lacunae take up about 60% of the plants volume.
An experiment was done to demonstrate the oxygen gradient in plants.It was found that a plant has 20% oxygen in its leaves, 15% in its stem,10% in the root parts, and only 2- 5% in the root hairs. The oxygen istaken in from the air by photosynthesis and travels through the plant andout the root hairs.
When low oxygen levels are present, plants use other mechanisms to adjustfor respiration. Aquatic plants can respire anaerobically. This has beenshown experimentally by bubbling N2 or O2 into the water with rhizomes,and then measuring the ethanol production. At <3% O2 , ethanol is producedby Typha, Scirpus, Nuphar, and others. Some aquatic plants have developedair roots along their stems for respiration in water. Aquatic trees havedeveloped pnuematophores which are extensions of the root system reachingabove the water level. Pnuematophores take in oxygen through small holesat their tips.
Other challenges that aquatic plants must adapt to include: floodingdesiccation (drying out) nutrient uptake vegetative reproduction