1. Salt Marshes II Ecology and Adaptations

2. IDEAL ZONATION - MS Abiotic toleranceBiotic competition

3. Characs of Tidal Wetlands Soil is saturated, anoxic (H 2 S = 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

4. 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 (C 3, C 4, CAM) Waterlogging and anaerobic soils N- competition – denitrifying bacteria Redox reactions in wetland soils

5. 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. C 4 photosynthesis)

6. 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).diffusion selectively-permeable membrane soluteconcentration selectively-permeable membranechemical potential chemical potential http://en.wikipedia.org/wiki/Osmosis

7. http://www.plantphys.net/chapter.php?ch=3 http://generalhorticulture.tamu.edu/lectsupl/Water/water.htmlhttp://www.plantphys.net/chapter.php?ch=3

8. Ψπ ΨpΨp Ψi = Ψp (turgor) + Ψπ (osmotic) Ψπ ΨpΨp ΨpΨp

9. ΨpΨp 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.

10. Pressure ConversionsPressure Conversions To ConvertMultiply ByTo Obtain psi0.06895bar psi0.00689476mPa psi6.89476kPa psi0.068atm bar14.4058psi mPa145psi kPa0.145psi atm14.696psi Pressure Conversion Factors GLYCOPHYTE = Cell osmotic potential (Ψ π ) = -0.5MPa at 100mol/m 3 ions (20% SW = 7ppt). HALOPHYTE: -2.5 MPa = -360 psi (12 x car tire!) = -25 atm at 500mol/m 3 ions (35ppt).

11. 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. C 4 photosynthesis)

12. 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.plant Example of SYMPLASTIC transport

13. The apoplast is interrupted by the Casparian strip in roots.Casparian striproots

14. Localization of Ions Hofmeister s. the sequence of ions arranged with respect to their effects on the solubility of proteins, e.g., on their salting-out effects. The lyotropic series was discovered in 1888 by Hofmeister and describes the effect of solutes on the structure and physical chemistry of the aqueous phase.

15. Osmolytes = osmotica 2 groups: – sugar/polyol based –N- or S-based GLYCOPHYTE = Cell osmotic potential (Ψ π ) = -0.5MPa at 100mol/m 3 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.

16. 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.metabolitephytoplanktonDMSsolar radiation S-based osmolytes

17. 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) hydrogenatedcarbohydratecarbonyl groupaldehydeketone reducing sugarhydroxyl group Polyols: Sugars: Monosaccharides and Disacch. Glycerol http://en.wikipedia.org/wiki/Monosaccharide Fructose (a Hexose) http://en.wikipedia.org/wiki/Disaccharide Sucrose

18. Reduce water loss Osmolyte balance – need to retain water Photosynthetic adaptations similar to DESERT plants! Spartina (& other grasses) – C 4 modification Succulents (Fam. Crassulacea) – CAM modification, does not appear to be used in saltmarsh plants even tho potentially beneficial. C 4 and CAM are spatial or temporal storage of C for the C 3 fixation reaction that each promote higher [CO 2 ] in leaf tissues, thereby reducing photorespiration inefficiency of Rubisco.

19. Photosynthetic pathways Light (ATP+NADPH) vs Dark (CO 2 -> sugars) reactions C 3 (PGA) is dark rct (Calvin cycle)

20. Photorespiration in C 3 plants: RUBISCO (rhymes with Nabisco) Evolved in low O 2 atmosphere O 2 is competitive substrate for CO 2 in this enzyme. C 4 – Calvin cycle CAM Two modifications to maintain high CO 2 for when stomata are closed in attempts to reduce water loss

21. Photosynthetic pathways Light (ATP+NADPH) vs Dark (CO 2 -> sugars) reactions C 3 (PGA) is dark rct (Calvin cycle) C 4 is modified C 3 with storage in mesophyll cells (mainly grasses) CAM is modified C 4, with Calvin cycle at night (mainly succulent plants).

22. Reduce water loss Osmolyte balance – need to retain water Photosynthetic adaptations similar to DESERT plants! Spartina (& other grasses) – C 4 modification Succulents (Fam. Crassulacea) – CAM modification, does not appear to be used in saltmarsh plants even tho potentially beneficial. C 4 and CAM are spatial or temporal storage of C for the C 3 fixation reaction that each promote higher [CO 2 ] in leaf tissues, thereby reducing photorespiration inefficiency of Rubisco.

23. 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

24. 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.zone of soilroots 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.

25. Aerenchyma Tidal flooding in mid-low marsh submerses roots for minutes-hours each day – anaerobic soils. Increase O 2 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

26. Aerenchyma Tidal flooding in mid-low marsh submerses roots for minutes-hours each day – anaerobic soils. Increase O 2 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/danal m/finalproj2.htm

27. http://www.plantstress.com/Articles/waterlogging_i/waterlog_i.htm

28. 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 organismssoilnitrateammonia 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.ammoniumnitritenitrification 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.denitrification atmosphere Anammox

29. Anammox Reaction Discovered in early 1980’s Biological process, in which nitrite and ammonium are converted directly into dinitrogen gas.nitriteammoniumdinitrogen 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.

30. Detailed N-cycle reactions Nitrogen fixation: N 2 (g) + 6 H + + 6 e − → 2 NH 3 by anaerobic bacteria, cyanobacteria. (http://en.wikipedia.org/wiki/Nitrogen_fixation )http://en.wikipedia.org/wiki/Nitrogen_fixation Nitrification: 2 step process, with step (1) usually rate limiting 1) NH 3 + CO 2 + 1.5 O 2 + Nitrosomonas → NO 2 - + H 2 O + H + 2) NO 2 - + CO 2 + 0.5 O 2 + Nitrobacter → NO 3 - Aerobic bacteria & archaea oxidize ammonia into nitrite followed by the oxidation of nitrite into nitrate. (http://en.wikipedia.org/wiki/Nitrification )ammonianitritenitrate.http://en.wikipedia.org/wiki/Nitrification PLANTS can use NH 4 + and NO 3 - (preferred) as N-source. Denitrification: reaction steps include NO 3 − → NO 2 − → NO + N 2 O → N 2 (g), anaerobic bacteria decomposing organic matter. (http://en.wikipedia.org/wiki/Denitrification )http://en.wikipedia.org/wiki/Denitrification Anammox reactions: NH 4 + + NO 2 − → N 2 (g), anaerobic bacteria, are v. specialized. (http://en.wikipedia.org/wiki/Anammox)http://en.wikipedia.org/wiki/Anammox

31. 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)

32. Plant Essential Nutrients

33. 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.electron moleculeatomionhydrogen oxygen –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.electron moleculeatomionoxygen hydrogen OiL RiG = Oxidation Loss Reduction Gain e -

36. METHANOGENESIS AEROBIC OXIDATION DENITRIFICATION

41. 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 (C 3, C 4, CAM) to reduce water loss in these “wetland” plants. Aerenchyma and rhizosphere – importance of O 2 in the root zone. Redox chemistry affects nutrient availability, anaerobic conditions promote diversity of bacteria.