1. Biology 561 Barrier Island Ecology
Halophytic Plants
Biology 561 Barrier Island Ecology

2. Niceties 80% of the earth is covered by saline water
Very few plants are able to tolerate saline conditions without serious damage
Plants that survive in saline environments are termed halophytes (c.f., glycophytes)
Most halophytes prefer saline conditions but can survive in freshwater environments
Most halophytes are restricted to
saline environments

3. What is a halophyte?
The term “halophyte” has not been precisely defined in the literature:
Plants capable of normal growth in saline habitats and also able to thrive on “ordinary” soil (Schimper, 1903).
Plant which can tolerate salt concentrations over 0.5% at any stage of life (Stocker, 1928).
Plants which grow exclusively on salt soil (Dansereau, 1957).

4. What is a halophyte? Categories of halophilism:
Intolerant Plants grow best at low salinity and exhibit decrease in growth with increase in salinity
Facultative Optimal growth at moderate salinity and diminished growth at both low and high salinities
Obligate Optimal growth at high or moderate salinity and no growth at low salinity

5. Hypothetical Glycophyte/Halophyte Growth in Various Salinities
Facultative Halophyte
Intolerant Halophyte
Growth 
Obligate Halophyte
Glycophyte
Salinity 

6. Halophytism in Higher Plants
Early plants developed in oceanic (i.e., high salinity) environments
Marine algae
Phytoplankton
Cyanobacteria
Land plants seem to have lost the
ability to thrive under high salt
conditions; most land plants are glycophytes
Cyanobacterium
Nostoc sp.
Marine algae (Codium sp.) grow and reproduce in waters with elevated salt content

7. Angiosperm Halophyte Types
Marine angiosperms
Mangroves
Coastal strand
Salt marshes

8. Saline Soils Possess large quantities of Na+
Na+ adsorption on clay particles reduces Ca++ and Mg++ content of soils
Marsh soils are typically:
Low in oxygen
High in carbon dioxide
High in methane
Marsh soils are constantly changing due to the ebb and flow of the tides

9. Osmotic pressure (atm)
Osmotic potentials of some halophytes of the eastern coast of United States
Species
Osmotic pressure (atm)
Seawater (New Jersey)
23.2
Spartina glabra
31.1
Spartina patens
Spartina michauxiana
Salicornia europaea
Distichlis spicata
28.8
Limonium carolinianum
Juncus gerardii
Baccharis halimifolia
26.1
Atriplex hastata
Hibiscus moschuetos
12.2

10. Contribution of NaCl to the osmotic potential (OP) of glycophytes and halophytes
Osmotic potential of plant sap (atm)
Species
OP of soil solution (atm)
OP calculated as NaCl
OP due to other substances
Total OP
Halophytes
Atriplex portulacoides
27.7
36.4
4.7
41.1
Salicornia fruticosa
20.6
31.7
9.6
41.3
Inula crithmoides
17.0
17.6
7.1
24.7
Statice limonium
10.5
18.5
5.0
23.5
Juncus acutus
9.3
11.9
7.5
19.4
Plantago coronopus
4.0
7.7
11.7
Glycophytes
Pistacia lentiscus A
4.5
20.1
24.6
Phillyrea latifolia
3.4
19.7
23.1
Pinus pinaster
6.9
15.0
21.9
Quercus ilex
2.2
26.8
A Osmotic potential was not measured but is presumably very low.

11. Water Potential
Water potential is a measure of the free energy (or potential energy) of water in a system relative to the free energy of pure water
The water potential symbol is psi, 
Unit of measure (pressure) = megapascals (Mpa) (10 Mpa = 1 bar [approx. 1 atmosphere])
Pure, free water w = 0 (the highest water potential value)

12. Components of Water Potential
w total water potential
m matric potential
s osmotic (solute) potential
p pressure (turgor) potential
g gravitational potential
Total water potential (w ) = m+s+p+ g

13. Typical Glycophyte w = m + s + p + g w = 0 + (-0.2) + 0.5 + 0
Plant
w = (-0.2)
w = -0.3
Water
w = m + s + p + g
Soil
w = (-0.2) (-4.0)
w = -0.2

14. Typical Halophyte w = m + s + p + g w = 0 + (-4.5) + 1.0 + 0
Plant
w = (-4.5)
w = -3.5
Water
w = m + s + p + g
Soil
w = (-3.0) (-4.0)
w = -3.0

15. Regulation of Salt Content in Shoots
Leaf surface containing salt gland of Saltcedar (Tamarix ramiosissima)
Secretion of salts
Salt exported via active
transport mechanism
Excretion includes Na+ and Cl- as well as inorganic ions
Photograph and schematic diagram of salt gland of Aeluropus litoralis
Two celled salt gland of Spartina

16. Salt Glands in Black Mangrove (Avicennia marina)
(a) sunken gland on upper epidermis; (b) elevated gland on lower epipermis b
Concentrations of secreted salts is typically so high that under dry atmospheric conditions, the salts crystallize

17. Regulation of Salt Content in Shoots
Salt leaching
Not well understood, but results from transport of salts to the near epidermis of leaves; precipitation leaches salts
Salt-saturated leaf fall
Leaves shed after accumulation of salts
Occurs in Hydrocotyle bonariensis and others

18. Responses to Increased Salts
Succulence Plant organs are thickened due to increased cellular water content
Increased growth Reduces cellular solute concentrations

19. Seed Dispersal in Halophytes
Most seeds of halophytes are buoyant
Examples are glasswort (Salicornia sp.), coconut (Cocos nucifera), sea rocket (Cakile sp.), and suaeda (Suaeda maritima)
Marine angiosperm seeds are not buoyant
Examples are Thalassia and Halophila

20. Germination in Halophytes
Germination inhibited by high salt concentrations
Chlorides are very toxic to germinating plants
Optimum germination is in freshwater
Germination response in salt water not necessarily correlated to later growth of a plant species under saline conditions
Higher temperatures slow germination in salt water

21. Physiological Response in Halophytes
Switch from Carbon-3 photosynthesis to CAM (crassulacean acid metabolism)
Stomates closed during
the day
CO2 fixation during
the night
Sugars accumulate in cells
Decrease osmotic pressure with organic ions (proteins)

22. Summary