Host Preferences of Arbuscular Mycorrhizal Fungi Colonizing Annual Herbaceous Plant Species in
Mycorrhizal Plant Interactions
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Transcript of Mycorrhizal Plant Interactions
Plant Nutrients
Just like us, plants require nutrients
C HOPKINS CaFe Mg- essential plant nutrients
Unlike us, (usually) plants do not get their nutrients from the food they eat. Instead get their nutrients from the surrounding environment
Major Sources of Nutrients Absorbed by Plants
Chapin, Matson, Mooney
Table 7.1. Major Sources of Nutrients that Are Absorbe d by Plantsa.
Source of plant nutrient (% of total)
Nutrient Deposition/fixation We athe ring Recycling
Temperate fore st ( Hubbard Brook)
Nitroge n 7 0 93
Phosphorus 1 < 10? > 89
Potassium 2 10 88
Calcium 4 31 65
Tundra (Barrow)
Nitroge n 4 0 96
Phosphorus 4 < 1 96
a Data from [Chapin, 1980 #1564; Whittaker, 1979 #2812]
Most Nutrients Are Picked Up By Diffusion
– Rates of diffusion depend on concentration gradient
• Rates of nutrient uptake are higher when the soil nutrient concentration is higher
– Rates of Mineralization and decomposition
– Amount of Fertilization
Depletion Zones
• Nutrient uptake by the root causes there to be a zone of nutrient depletion around the root
– Roots need to keep growing to explore new soil
Chapin, Matson, Mooney
Increasing root area is main way plants can increase nutrient
uptake
• Increased root:shoot ratio
– Increased investment in roots
• Root proliferation in nutrient hot spots
– Root growth occurs where it does the most good
• Longer root hairs
Root Shoot Ratios Depend on Soil Nutrient Supply
Effect of Soil Phosphorous on Root: Shoot Ratios
Low Soil Phosphorous Content
Root Mass (mg Shoot Mass (mg) Root:Shoot Ratio223 877 0.24
High Soil Phosphorous Content
Root Mass (mg Shoot Mass (mg) Root:Shoot Ratio209 1324 0.16
Q: Why are fine structures like hyphae and root hairsparticularly effective at nutrient absorption?
A: Have high surface area.
Q: For a given volume (or mass) of roots, what size rootpresents the most surface area?
Surface area of a cylinderSA = circumference x length
SA = x diam x lengthSA = x 2r x length
Volume = area x lengthVol = x r2 x length
SA/Vol = ( x 2r x length)/( x r2 x length)
SA/Vol = 2/r
As the radius decreases, the surface area per volume increases.
Importance of Diameter For Nutrient Uptake
Fungi
• Unique, weird, interesting, and important group of organisms
– You should be able to tell us
– About their basic biology
• How they are unique
• Why they are weird
• Why they are interesting
• Why they are important
Fungi
• Eukaryotic, spore-bearing, heterotrophic organisms that produce extracellular enzymes and absorb their nutrition.
• Functional definition
Fungi vs. "fungi"
• Based on the functional definitions of fungi, fungi do not comprise a single monophyletic group of organisms
• more than one evolutionary origin
• not all "fungi" are members of the Kingdom Fungi Fungi
Fungi
• The Kingdom Fungi includes some important organisms, both in terms of their ecological and economic roles. – break down dead organic material
• Nutrient cycling
– most vascular plants have mycorrhizae– provide numerous drugs
• E.g., penicillin
– Provide food • mushrooms, truffles and morels• Involved in producing bread, wine. champagne, and beer.
Fungi
• Cause a number of plant and animal diseases
– Humans
• ringworm, athlete's foot, and several more serious diseases are caused by fungi.
– Because fungi are more chemically and genetically similar to animals than other organisms, this makes fungal diseases very difficult to treat.
– Plant diseases
• rusts, smuts, and leaf, root, and stem rots, and may cause severe damage to crops.
Fungi
• About 100,000 species have been described
– Some have suggested that there might be over 1 million species of undescribed Fungi
Fungi Systematics
• Fungi are usually classified in four divisions: – Chytridiomycota (chytrids),
– Zygomycota (bread molds)
– Ascomycota (yeasts and sac fungi)
– Basidiomycota (club fungi).
• Classification based on the way in which the fungus reproduces sexually. – The shape and internal structure of the
sporangia, which produce the spores
Fungi Systematics
• The Deuteromycota includes all fungi which have lost the ability to reproduce sexually.
– Don’t know which group they should be placed
• Deuteromycota becomes a convenient place to dump them until someone gets around to working out their biology.
Fungi Systematics
Lichens are not a single organism, but rather a symbiotic association between a fungus and an alga.
– The fungus is usually an ascomycete or basidiomycete
– the alga is usually a cyanobacterium or a green alga.
• Often the fungal partner is unable to grow without the algal symbiont, making it difficult to classify these organisms.
fungi that are not Fungi
• It should also be noted that some organisms carry the name of mold or fungus, but are NOT classified in the Kingdom Fungi.
• These include the slime molds and water molds (Oomycota).
– The slime molds are now known to be a mixture of three or four unrelated groups
– oomycetes are now classified in the Chromista, with the diatoms and brown algae.
Fungal Organelles
• Fungi are eukaryotes so they share the normal eukaryotic organelles
– Lack cholorplasts
• Fungal organelles
– Spitzenkorper
• associated with growing hyphal tips in septate fungi
– chitosome
• microvesicles transporting chitin synthases to growing cell wall
Cell Wall
• chitin
1-4 n-acetyal glucosamine
• -glucans
polymers of glucose
1-3 glucose
• cellulose
• Key Point
• Fungal cell walls
different from plant
cell wallsin some
Chitin
Cellulose
1-3 glucan
Body Plan• unicellular (yeast), filamentous, or both (=dimorphic)
• Hypha (pl. hyphae) is the basic “cellular” unit in filamentous fungi; they may be septate or coenocytic(aseptate);
• collectively known as a mycelium
• limited tissue differentiation and division of labor
Nuclear Status
• Eukaryotic; uni, bi- or multinucleate
• Haploid, diploid (less frequent)
• Monokaryon
(1 nucleus per hyphal compartment)
• Dikaryon
(2 nuclei per hyphal compartment)
• Homokaryotic
• Heterokaryotic
Feeding• Heterotrophic
• Secrete extracellular enzymes
• Absorptive nutrition
• Saprobes
• decay dead organic matter
• pathogens
• symbionts
• Parasites, commensals, mutualists
Reproduction
• Sexual reproduction:
• spores meiotically produced nuclei
• Asexual reproduction
• Spores with mitotically produced nucleiierivenuclei
Spores - a minute propagative unit functioning as a seed, but differing from it in that a spore does not contain a preformed embryo
Fruiting body - any complex fungal structure that contains or bears spores; a sporocarp
Sexual Reproduction in Fungi
• Homothallic (selfing)
• Heterothallic (outcrossing)– Monoecious or dioecious
• Genetic mating system
– Different Mating Types• Generally can’t mate with someone with same mating type
– 1 to hundreds of mating types
– Some people use “mating types” and “sexes” as synonyms
What is a “Sex”?
• I prefer to distinguish between mating types and sex.
• Questions:
– How many sexes in humans?
– How many sexes are you?
Sexes in Humans
• We consider that humans have two sexes– Females and males
• What distinguishes males and females?– In humans individuals that produce eggs (female
gametes) are called females
– Individuals that produce sperm (males gametes) are called males
• Humans are “dioecious”– Female and male gametes are produced in different
individuals
Hermaphrodites• Some species (earthworms, sea hares, lots of
plants) produce both male and female gametes
– Hermaphrodites
– Monoecius
Do All Sexually Reproducing Species Produce Two Species?
• What does it mean to have two sexes?
• What would it mean to have one, three, or eleven species?
What Would It Mean to Have Other Than Two Sexes?
• We produce two types of gametes
– Consider that we have two sexes
• Let’s think about our life cycle?
Human Life Cycle
• Gametes (haploid) produced by meiosis
• Haploid gametes join to make zygote (diploid)
• We have “alternation of generations”
– Both diploid and haploid stage of our life cycles
Aside
• When does life begin?• Actually a very difficult
question to answer because of the life cycle, life never really stops.
• Not a question that science can answer
Back to Number of Sexes
• We produce 2 types of gametes – Therefore we have two sexes
• Difference in Size and Function of Gametes– Female gametes (eggs)
• Large
• Immobile
– Male gametes (sperm)• Small
• mobile
What Would It Mean to Have Three Sexes
• Three sizes and function of gametes?
– Small mobile gametes
– Large immobile gametes
– Intermediate-sized mobile gametes
• What happens during fertilization?
• No species that have three sexes
What Would it Mean To Have Only One Sex?
• One size and function of gamete.
– Mobile
– Contain resources
• Swimming Egg
• Huge Sperm
Isogametes
• Chlamydamonas– Green algae– Single celled– Haploid as adults– aquatic
• Single celled• Photosynthetic• Eye spot
• Haploid adult produces isogametes by mitosis– Haploid, mobile, contain
energy
Isogametes
• Isogametes are evolutionarily “primitive”
– First organisms that reproduced sexually via gametes were isogamous
• Oogametes (egg and sperm) are evolutionarily advanced
• Oogametes arose from isogametes via disruptive selection
Large gametes- contain more
resources, thus mighthave higher survival once fertilized
Small gametes- can make more of
Them and the might be More mobile, thusFertilize gametes more often
SelectionAgainst middle-Sized gametes
Female gametes- specialized for
Providing resources to embryo
Male gametes- specialized for
mobility during fertillization
Mycorrhizae
• Mycorrhizas are symbiotic associations essential for one or both partners, between a fungus and a root of a living plant, that is primarily responsible for nutrient transfer. – Mycorrhizas occur in a specialized plant organ where
intimate contact results from synchronized plant-fungus development.
• The name mycorrhizas, which literally means fungus-root, was invented by Frank (1885) for non-pathogenic symbiotic associations between roots and fungi.
Types of Mycorrhizae
• Ectomycorrhizal fungi
– are mostly basidiomycetes that grow between root cortical cells of many tree species, forming a Hartig net.
• Arbuscular mycorrhizal fungi
– form highly branched structures called arbuscules, within root cortical cells of many herbaceous and woody plant species.
Ectomyhcorrhizae
• Produce hyphae between root cortical cells producing a netlike structure called the Hartignet
Ectomycorrhizae
• Found on woody plants ranging from shrubs to forest trees
– Pinaceae (Pines)
– Fagaceae (Oaks)
– Betulaceae (Beeches)
– Myrtaceae (Myrtles)
Ectomycorrhizae
• Over 4,000 fungal species, belonging primarily to the Basidiomycotina, and fewer to the Ascomycotina, are known to form ectomycorrhizae.
• Many of these fungi produce mushrooms and puffballs on the forest floor.
• Some fungi have a narrow host range while others have very broad host range– Some species of fungi forms ectomycorrhiza with
more than 46 tree species belonging to at least eight genera.
Vesicular Arbuscular Mycorrhiza
Inside root
• Intercellular mycelium
• Intracellular arbuscule
• tree-like haustorium
• Vesicle with reserves
Outside root
• Spores (multinucleate)
• Hyphae
•thick runners
•filamentous hyphae
Form extensive network of hyphae
even connecting different plants
Arbuscular Mycorrhiza
• Form highly branched arbuscule within root cortical cells.
• The fungus initially grows between cortical cells, but soon penetrates the host cell wall and grows within the cell.
• The general term for all mycorrhizal types where the fungus grows within cortical cells is endomycorrhiza. I
Arbuscular Mycorrhizae
• Glomales (130 species – infects 300,000 plant species)
• Found on roots of herbaceous angiosperms, most trees, mosses, ferns…
• not present on Cruciferae, Chenopodiaceae, Proteaceae
• small biomass compared to roots
Mycorrhizae and Orchids
• Orchids typically have very small seeds with little nutrient reserve.
• The plant becomes colonized shortly after germination, and the mycorrhizal fungus supplies carbon and vitamins to the developing embryo.
Root hair Smallest hyphae
• Roots and root hairs
cannot enter the smallest
pores
• Hyphae is 1/10th
diameter of root hair
• Increased surface area
•Surface area/volume of a
cylinder:
SA/vol ≈ 2/radius
Why Mycorrhiza?
Plant-Mycorrhizal Interactions
• Mycorrhiza have been shown to increase rates of nutrient (especially phosphorous) uptake
• May also increase rates of water uptake
Plant-Mycorrhizal Interactions
• General Trends
– Because mycorrhiza increase rates of nutrient uptake plants “infected” with mycorrhizae have lower root/shoot ratios
– Usually mutualistic relationship
• Plants benefit from increased nutrient uptake
• Mycorrhiza benefit from carbon
Importance of Animal-Generated Disturbances
• Open potential germination sites by removing leaf litter
• Create patches that differ
– Nutrient content
– Microbial content
Experimental Approach
• As part of a larger experiment we grew plants in soil from different disturbances
– Gopher mounds
– Bare space
– Rabbit mounds
• With and without mycorrhiza
Schizachyrium scoparium
Experimental Design
• Grew seedlings in “conetainers” in greenhouse
• Sterilized soil (heat)• Selectively added back
microbes (sterilized, + mycorrhiza, + bacteria, + both)
• Grew seedlings– Growth rate, root &
shoot biomass, mycorrhizalifection
Some Results
• Plants infected with mycorrhiza had lower root/shoot ratios
• Soil from rabbit mounds– Higher in nitrogen
than surrounding soil (equal in all other nutrients)
Results
• Prediction– If mycorrhiza-plant interaction is mutualism then
plants infected with mycorrhiza should grow better than plants grown in sterilized soil
• Observation– Plants grown in sterilized soil were larger than
plants infected with mycorrhiza
– Mycorrhiza acted as parasite in high nutrient environments.