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• Obligate halophytes vs glycophytes• Osmosis and osmolytes• Water potential and ions• Organic osmolytes (=osmotica):

– Sugar, polyol-based– N-based (proline, betaines) & S-based (DMS)

• 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=3http://generalhorticulture.tamu.edu/lectsupl/Water/water.html

Ψπ

Ψp

Ψi = Ψp (turgor) + Ψπ (osmotic)

Ψπ

Ψp

Ψπ

Ψp

Ψπ

Ψp

Ψi = Ψp (turgor) + Ψπ (osmotic)

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.

Pressure Conversions

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

Pressure Conversion Factors

• 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 transportThe 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.

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.

S-based osmolytes

Carbohydrate-based Osmotica

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)

• Polyols:

• Sugars: Monosaccharides and Disacch.

Glycerol

http://en.wikipedia.org/wiki/Monosaccharide

Fructose (a Hexose)

http://en.wikipedia.org/wiki/Disaccharide

Sucrose

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)

Photorespiration in C3 plants:RUBISCO (rhymes with Nabisco)Evolved in low O2 atmosphereO2 is competitive substrate for CO2 in this enzyme.

C4 – Calvincycle

CAM

Two modifications to maintain high CO2 for when stomata are closed in attempts to reduce water loss

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 sulfide-toxicity, 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• 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.

An

amm

ox

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 → NO3-

Aerobic 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-

METHANOGENESIS

AEROBIC OXIDATION

DENITRIFICATION

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.