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Ecological significance of mycorrhizae in ferns
Overview of Mycorrhizae
My “Predicted patterns”
G.T.S Baylis' theory of root morphology (1976)
Boullard confirms theory applies to pteridophytes (1979)
Further research supports theory (S. M. Berch, B. Kendrick, 1982)
Hawaiian contradiction ( J. N. Gemma, et al 1992)
Cheilanthes lanosa study (Palmieri and Swatzell, 2004)
Other Significant VAM occurrences in ferns
Overview of Mycorrhizae
Two types of associations
Endomycorrhizal fungi- (Vasicular Arbuscular) mycorrhizal fungi-colonize hosts roots intracellularly
Ectomycorrhizal- colonize hosts roots extracellularly, form hyphal sheath that surrounds root tip
All Mycorrhizae are symbiotic, usually mutualistic, sometimes pathogenic
Focus on VAM in ferns
Vesicular-arbuscular mycorrhizas (VAM)
No known sexual state
Fungal hyphae penetrate root cells and form intricately branched, shrub-like arbuscles within the cells
Over 200 species described, most can colonize most VAM plant species
Top picture-”infection” site
Bottom- arbuscule (nutrient transfer)
How does it work?
Fungi release powerful enzymes that dissolve tightly bound minerals like phosphorus, sulfur, iron and all the major and minor nutrients used by plants
Fungi receive translocated root sugars from the host plant
Fungi translocates these sugars to surrounding mycelium
Benefits of Mycorrhizal relationships
Increase establishment and survival chance by;
-Increase root uptake potential by ten to several thousand fold
-Reduce drought stress by storing water during dry periods
VAM increases plant uptake of Phosphorus, Nitrogen Potassium, Magnesium, Copper, Zinc, Calcium, Iron, Cadmium, Nickel, and Uranium
Possible uses for bioremediation, agriculture, and restoration
(S. Bray et. Al 2003, Gail W.T. Wilson et. Al, 2001,, Janos, 1980)
Patterns seen in vascular plants
Mycorrhizae increased either growth or survival in 24 of 28 species studied.
No ferns included in study
Do ferns adhere to this pattern?
(Janos, 1980)
What I expected to find in Ferns
Ferns, being among the oldest vascular plants found today would take advantage of mycorrhizal symbiosis.
Ferns in extreme habitats would predominantly have symbiosis with fungi
Dispersal would be more likely to occur in habitats where AMF is present
Baylis Theory of root morphology
Theory put forth in 1972, states;
“Primitive” fleshy roots lack root hairs and are thus highly colonized by hyphae to maintain uptake ability
“Advanced” fine roots less so, already having sufficient nutrient uptake
Boullard 1979 confirms that Baylis' theory holds true in pteridophytes, stated further that evolution in pteridophytes is accompanied by mycotrophy decline
(Berch, Kendrich, 1982)
Vesicular-Arbuscular Mycorrhizae of Southern Ontario Ferns and Fern-Allies(Shannon M. Berch and Bryce Kendrick 1982)
Three features of VAM sparked the need for study
1) The mycorrhiza-dependance of certain agriculturally valuable plants under conditions of poor nutrition
2) The apparant lack of host-specificity of the fungus
3) The ubiguity of the symbiosis in nature
This Study
39 Species from 17 genera from the Southern Ontario flora studied
Vesicular-Arbuscular Mycorrhizae of Southern Ontario Ferns and Fern-Allies(Shannon M. Berch and Bryce Kendrick 1982)
Methods
39 Fern species collected, including 4 Equisetum, and 2 Lycopodium species
Root segments were placed in 50% formalin-acetic acid-alcohol (FAA) for >3 months
Washed and heated in 10% KOH for >2h
Second wash, roots teased apart to isolate “fine” roots
These fine roots were cut into 5-mm long segments
100 segments per plant were stained and searched for arbuscule presence
Results
Ferns on bare rock and crevices showed no VAM
Most fern species showed VAM associations to some extent
Infestation varied drastically in several species, see Onoclea sensibilis, from 0%-80% infection
Root hairs and Mycorrhizae clusters and patterns varied significantly from plant to plant
State that results support Baylis' and Boullard's theory due to ophioglossales findings
(Berch, Kendrich, 1982)
Interpretation
Pattern of epilithic ferns lacking mycorrhizae most likely due to lack of microorganism competition for nutrients
Findings “support” Baylis theory of root development, although these findings were mostly in Ophioglossales
Plants vary in the presence of VAM, pattern of infection and abundance
Questions
Does root hair presence affect infection of roots?
Does infection of roots prevent root hair development?
No studies found testing this correlation
Mycorrhizae in Hawaiian Pteridophytes: Occurrence and Evolutionary Significance
J. N. Gemma, R. E. Koske and T. Flynn (1992) The unique flora of Hawaii offered an
opportunity to study a large proportion of the population for the presence of VAM
VAM presence in ferns largely unknown in Hawaii, Angiosperms largely mycorrhizal
Do the patterns seen in the US hold true in HI?
Roots collected over a two year period on several of the Hawaiian islands from varied substrates and habitats from 45% of fern species-(72 native and 17 naturalized)
Mycorrhizae in Hawaiian Pteridophytes: Occurrence and Evolutionary Significance
J. N. Gemma, R. E. Koske and T. Flynn (1992)
Methods
Methods very similar to previous study
Plant species were identified as either
M = consistently mycorrhizal
N = consistently non-mycorrhizal
M + N = facultative mycorrhizal (presence and absence seen in same species)
MI (mycorrhizal index) used to quantify intensity of infection
Mycorrhizae in Hawaiian Pteridophytes: Occurrence and Evolutionary Significance
J. N. Gemma, R. E. Koske and T. Flynn (1992)
Results
Higher percentage of epilithic VAM found (86%)
Higher percentage of epiphytic VAM found (55%)
These were previously consider rare or absent (Berch and Kenrich 1982)
Contradiction to Boullard-mycotrophy was found to occur with equal frequency in primitive and advanced ferns
Fossil records show high percentage of non-mycotrophic ferns, (not current flora)
Mycorrhizae in Hawaiian Pteridophytes: Occurrence and Evolutionary Significance
J. N. Gemma, R. E. Koske and T. Flynn (1992)
Interpretation
Extremely low percentage of Mainland ferns surveyed for VAM as compared to HI (1.5% TO 44.5%)
Evolutionary correlation put forth by G.T.S. Baylis may be unfounded, more research needed
As VAM is established, facultative and obligate species flourish
Mycorrhizal Fungi associated with Cheilanthes LanosaM. Palmieri and L.J. Swatzell (2004)
Cheilanthes lanosa- (lip fern) xerophytic fern, grows on dry, exposed rocky outcrops
Least resistant to desiccation when compared to Selaginella lepidophylla,(Resurrection Plant), and Notholaena sinuatA var. cochisensis, (Waxy Cloak Fern)
Ability to thrive as successfully as those mentioned unclear
Spore germination requirements do not vary from their mesic counterparts
How are these ferns thriving in arid conditions?
Palmieri and Swatzell hypothesized that survival could depend upon mycorrhizal symbionts
VAM not previously described for cheilanthoid ferns (Boullard 1979)
Mycorrhizal Fungi associated with Cheilanthes LanosaM. Palmieri and L.J. Swatzell (2004)
13 plants surveyed from 3 sites in Illinois and Missouri
Methods, once again similar
Isolated spores from the soil matrix and an attempt was made to try and identify them
Pictured-cross section of root segment
Results
Ferns collected from 3 sites, 1 in Missouri, 2 in Illinois
All roots found to be associated with VAM
Interpretation
VAM may enable Cheilanthes ferns to thrive in areas previously unsuitable
Results went against pattern put forth by Boullard
In Polypodiaceae family, one of the more advanced families of ferns
Questions
What are the morphological and environmental differences between VAM and non-VAM ferns of extreme habitats?
What is the driving force behind VAM association?
A Couple of interesting findings
(Agely et. Al 2004) found that VAM increase Arsenic uptake by the Chinese Brake Fern
(K. Turnau et. Al 2004) found that The presence of VAM fungi in both gametophytes and sporophytes of Pallaea viridis resulted in larger leaf area and root length of the sporophyte
Future research
What role has VAM played in the dispersal pattern of ferns
-Has it enabled ferns to live in extreme conditions?
-Do VAM ferns have an advantage over non-VAM species?
Does VAM presence or absence impact root hair development?
Is the pattern seen in Hawaii typical of other island? Mainland?
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