Download Salt Marshes II

Salt Marshes II
Ecology and Adaptations
IDEAL ZONATION - MS
Abiotic tolerance
Biotic competition
Characs of Tidal Wetlands
• Soil is saturated, anoxic (H2S = smell)
• Rhizosphere = oxygenated zone around roots
(Redox chemistry)
• Plants adaptations to tolerate salt (halophytes)
• Innundated by tides – low energy coasts
• Sediment deposition = nutrient inputs
• Microbial community breaks down organic
matter (Redox chemistry).
• High diversity of plants, animals, microbes
Some key concepts
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Obligate halophytes vs glycophytes
Osmosis and osmolytes
Water potential and ions
Organic osmolytes (=osmotica):
– Sugar, polyol-based
– N-based (proline, betaines) & S-based (DMS)
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•
•
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Photosynthetic pathways (C3, C4, CAM)
Waterlogging and anaerobic soils
N- competition – denitrifying bacteria
Redox reactions in wetland soils
OSMOSIS
• Defn: Osmosis is the diffusion of a solvent through a
selectively-permeable membrane from a region of low
solute concentration to a region of high solute
concentration, or in other words, from a high water
concentration to a low water concentration. The
selectively-permeable membrane is permeable to the
solvent, but not to the solute, resulting in a chemical
potential difference across the membrane which drives
the diffusion. That is, the solvent flows from the side of
the membrane where the solution is weakest to the side
where it is strongest, until the solution on both sides of
the membrane is the same strength (that is, until the
chemical potential is equal on both sides).
• http://en.wikipedia.org/wiki/Osmosis
•
http://www.plantphys.net/chapter.php?ch=3
http://generalhorticulture.tamu.edu/lectsupl/Water/water.html
Ψi = Ψp (turgor) + Ψπ (osmotic)
Ψp
Ψp
Ψp
Ψπ
Ψπ
Ψπ
Ψi = Ψp (turgor) + Ψπ (osmotic)
Ψp
BALANCE of Turgor and Osmotic
pressures are achieved by
REGULATION of dissolved ions
(salts) and organic osmolytes.
IMBALANCE results in “wilting” or
“overfilling” of cell -> both are
undesirable.
Ψπ
Pressure Conversion Factors
To Convert
Multiply By
To Obtain
psi
0.06895
bar
psi
0.00689476
mPa
psi
6.89476
kPa
psi
0.068
atm
bar
14.4058
psi
mPa
145
psi
kPa
0.145
psi
atm
14.696
psi
• GLYCOPHYTE = Cell osmotic potential (Ψπ)
= -0.5MPa at 100mol/m3 ions (20% SW = 7ppt).
• HALOPHYTE: -2.5 MPa = -360 psi (12 x car
tire!) = -25 atm at 500mol/m3 ions (35ppt).
Salt-tolerance
• Salt = Na+Cl• Salt regulation:
– Ion exclusion at roots
– Succulent growth = dilution
– Concentration and shedding of leaves
– Secretion (salt glands = trichomes)
– Root discharge to rhizosphere
– Reduce water loss (e.g. C4 photosynthesis)
Apoplastic vs Symplastic transport
The symplast of a plant is the space at the inner side of the plasma membrane,
the apoplast is the free diffusional space outside the plasma membrane.
Example of SYMPLASTIC transport
The apoplast is interrupted by the Casparian strip in roots.
Osmolytes = osmotica
• 2 groups:
– sugar/polyol based
– N- or S-based
• GLYCOPHYTE = Cell osmotic potential (Ψπ) =
-0.5MPa at 100mol/m3 ions achieved by 30g/L
hexose (monosaccharide) or 60g/L of disacch.
• The production of these is NOT free – a
photosynthetic cost, energy not available for
growth, reproduction, etc.
N-based osmolytes
Proline – amino acid
Quaternary ammonium cation.
Any or all of the R groups may
be the same or different alkyl
groups. Also, any of the R
groups may be connected.
S-based osmolytes
Dimethylsulfoniopropionate ((CH3)2S+CH2CH2COO−; more frequently abbreviated
to DMSP), is a metabolite found in marine phytoplankton and some species of terrestrial
plants. Although originally considered to act only as an osmolyte, several other
physiological and environmental roles have also been discovered. DMS is thought to
play a role in the earth's heat budget by decreasing the amount of solar radiation that
reaches the earth's surface.
Carbohydrate-based Osmotica
• Polyols:
Glycerol
A sugar alcohol (also known as a polyol, polyhydric alcohol, or polyalcohol) is a
hydrogenated form of carbohydrate, whose carbonyl group (aldehyde or ketone,
reducing sugar) has been reduced to a primary or secondary hydroxyl group. (USED AS
ARTIFICIAL SWEETENERS)
• Sugars: Monosaccharides and Disacch.
Fructose (a Hexose)
Sucrose
http://en.wikipedia.org/wiki/Monosaccharide
http://en.wikipedia.org/wiki/Disaccharide
Reduce water loss
• Osmolyte balance – need to retain water
• Photosynthetic adaptations similar to DESERT
plants!
• Spartina (& other grasses) – C4 modification
• Succulents (Fam. Crassulacea) – CAM
modification, does not appear to be used in
saltmarsh plants even tho potentially beneficial.
• C4 and CAM are spatial or temporal storage of C
for the C3 fixation reaction that each promote
higher [CO2] in leaf tissues, thereby reducing
photorespiration inefficiency of Rubisco.
Photosynthetic
pathways
• Light (ATP+NADPH)
vs Dark (CO2 ->
sugars) reactions
• C3 (PGA) is dark rct
(Calvin cycle)
C4 – Calvin
cycle
Two modifications to maintain high CO2 for when
stomata are closed in attempts to reduce water loss
Photorespiration in C3 plants:
RUBISCO (rhymes with Nabisco)
Evolved in low O2 atmosphere
O2 is competitive substrate for
CO2 in this enzyme.
CAM
Photosynthetic
pathways
• Light (ATP+NADPH) vs
Dark (CO2 -> sugars)
reactions
• C3 (PGA) is dark rct
(Calvin cycle)
• C4 is modified C3 with
storage in mesophyll cells
(mainly grasses)
• CAM is modified C4, with
Calvin cycle at night
(mainly succulent plants).
Reduce water loss
• Osmolyte balance – need to retain water
• Photosynthetic adaptations similar to DESERT
plants!
• Spartina (& other grasses) – C4 modification
• Succulents (Fam. Crassulacea) – CAM
modification, does not appear to be used in
saltmarsh plants even tho potentially beneficial.
• C4 and CAM are spatial or temporal storage of C
for the C3 fixation reaction that each promote
higher [CO2] in leaf tissues, thereby reducing
photorespiration inefficiency of Rubisco.
Waterlogged soils
• Anaerobic – oxygen used up rapidly in
upper few cms. Rich in organic matter.
• Soil microbial community very diverse
• N-denitrifiers compete with plants.
• Sulfate-reducers produce toxic sulfides.
• Plants need to get oxygen to roots –
aerenchyma system of air spaces
WATERLOGGING
• Rhizosphere is the zone of soil that is directly
influenced by roots and associated soil
microorganisms. This effect is by transfer of root
exudates and root tissue to soil.
• Oxygenation by aerenchyma reduces sulfidetoxicity, promotes aerobic bacterial action
(nitrification!).
• Exclusion of ions may increase “saltiness”
altering the osmotic potential required to
maintain positive water gain into plant.
Aerenchyma
• Tidal flooding in mid-low marsh submerses roots
for minutes-hours each day – anaerobic soils.
• Increase O2 diffusion to roots from leaves
• Pore space in tissues of wetland plants (60%) vs
terrestrial plants (2-7%).
• Can be loosely packed cortical parenchyma
cells or organized “vascular” system.
• Very extensive in Juncus, S. alterniflora, D.
spicata
Aerenchyma
• Tidal flooding in mid-low marsh submerses roots
for minutes-hours each day – anaerobic soils.
• Increase O2 diffusion to roots from leaves
• Pore space in tissues of wetland plants (60%) vs
terrestrial plants (2-7%).
• Can be loosely packed cortical parenchyma
cells or organized “vascular” system.
• Very extensive in Juncus, S. alterniflora, D.
spicata
• http://www.tau.ac.il/~ecology/virtau/danalm
/finalproj2.htm
http://www.plantstress.com/Articles/waterlogging_i/waterlog_i.htm
N-cycle
Anammox
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•
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Plants get nitrogen from the soil by
absorption at their roots in the form of
either nitrate ions or ammonia.
Ammonia is produced in the soil by
nitrogen fixation by nitrogen fixing
organisms
Another source of ammonia is the
decomposition of dead organic matter
by bacteria called decomposers, which
produce ammonium ions (NH4+). In
well-oxygenated soil, these are then
oxygenated first by bacteria into nitrite
(NO2-) and then into nitrate. This
conversion of ammonia into nitrate is
called nitrification.
During anaerobic (low oxygen)
conditions, denitrification by
bacteria occurs. This results in
nitrates being converted to nitrogen
gas and returned to the
atmosphere. In addition Anammox
can directly convert nitrite +
ammonium to nitrogen gas.
Anammox Reaction
• Discovered in early 1980’s
• Biological process, in
which nitrite and ammonium are converted
directly into dinitrogen gas.
• This process contributes up to 50% of the
dinitrogen gas produced in the oceans.
• It is thus a major sink for fixed nitrogen
and so limits oceanic primary productivity.
Detailed N-cycle reactions
• Nitrogen fixation: N2 (g) + 6 H+ + 6 e− → 2 NH3 by anaerobic
bacteria, cyanobacteria.
(http://en.wikipedia.org/wiki/Nitrogen_fixation )
• Nitrification: 2 step process, with step (1) usually rate limiting
1) NH3 + CO2 + 1.5 O2 + Nitrosomonas → NO2- + H2O + H+
2) NO2- + CO2 + 0.5 O2 + Nitrobacter → NO3Aerobic bacteria & archaea oxidize ammonia into nitrite
followed by the oxidation of nitrite into nitrate.
(http://en.wikipedia.org/wiki/Nitrification )
• PLANTS can use NH4+ and NO3- (preferred) as N-source.
• Denitrification: reaction steps include NO3− → NO2− → NO
+ N2O → N2 (g), anaerobic bacteria decomposing organic
matter. (http://en.wikipedia.org/wiki/Denitrification )
• Anammox reactions: NH4+ + NO2− → N2 (g), anaerobic bacteria,
are v. specialized. (http://en.wikipedia.org/wiki/Anammox)
Liebig’s Law of the Minimum (1840)
• The yield potential of a
crop is like a barrel with
staves of unequal length.
The capacity of the barrel
is limited by the length of
the shortest stave (in this
case, nitrogen), and can
only be increased by
lengthening that stave.
When that stave is
lengthened, another one
becomes the limiting
factor.
• Plant Macronutrients (6)
and micronutrients (7)
Plant Essential Nutrients
REDOX reactions
• The term redox comes from the two concepts of
reduction and oxidation.
– Oxidation describes the loss of an electron by a
molecule, atom, or ion; loss of hydrogen, or gain of
oxygen. It also means an increase in oxidation
number.
– Reduction describes the uptake of an electron by a
molecule, atom, or ion; loss of oxygen or gain of
hydrogen. It also means a decrease in oxidation
number.
• OiL RiG = Oxidation Loss <–> Reduction Gain e-
AEROBIC OXIDATION
DENITRIFICATION
METHANOGENESIS
SUMMARY
• Are saltmarsh plants obligate halophytes?
• Osmosis, Water potential, and ionic osmolytes
• Organic osmolytes (=osmotica):
– Sugar, polyol-based
– N-based (proline, betaines) & S-based (DMS)
• Photosynthetic pathways (C3, C4, CAM) to reduce water
loss in these “wetland” plants.
• Aerenchyma and rhizosphere – importance of O2 in the
root zone.
• Redox chemistry affects nutrient availability, anaerobic
conditions promote diversity of bacteria.