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In lowland rainforest in Sulawesi, how many of the 1250 beetle species feed directly on fungal fruit bodies or on fungal mycelium in wood
40%
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What are mycorrhizas
mutualistic associations between fungi and plant roots
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what percentage of vascular rain forest plants regularly form associations with mycorrhizal fungi
75-80%
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According to Kiers et al (2000) why has the mutualism between mycorrhizal fungi and plant roots been formed?
transport of carbohydrate to the fungus, and mineral nutrients + water to the plant. This improves plant nutrient uptake and drought tolerance, reduces vulnerability to plant pathogens
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What is the difference between the two main mycorrhiza types: arbuscular and ectomycorrhizas?
- Arbuscular: limited ability to degrade organic matter (AM)
- Ectomycorrhizas- can access nutrients from labile organic material that is otherwise unavailable to plants (EM)
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AMs are common and widespread and grow into the root cortex forming what within cortex cells? what are these responsible for?
highly branched structures (arbuscules) which are responsible for nutrient exchange between host and fungus
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EMs are the second most abundant and evolved when
more recently
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what kind of habitats are EMs adapted to on a global scale
rich in organic material
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What select range of species are EMs associated with
predominantly woody spp (pinaceae, dipterocarpaceae, fagaceae, eucalyptus, fabaceae, nyctaginaceae) incl certain tree families and genera that form monodominant stands
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What are additional forms of mycorrhiza and what do they do?
ericoid mycorrhizas, associated with orchids and Ericaceae. They decompose humic material.
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These associations between ericoid mycorrhizas are generally viewed as mutualistic, but what may happen in some cases of orchid mycorrhizas
they can behave as pathogens and saphrophytes and may gain little from orchids
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what plants avoid mycorrhizal associations altogether?
colonists of open groud (Proteaceae), haustorial parasites (mistletoes), carnivorous species (Drosera, Droseraceae) and those like sedges (Cyperaceae) that live in waterlogged anoxic soils
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plants without mycorrhizas usually have what
finer roots, more root hairs and relatively advance chemical defences
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What did Hawksworth and Rossman 1997 estimate to be the number of extant fungal spp globally based on a plant-fungi ratio of 1:6?
1.5mil
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However, plant-fungal ratios of around 1:33 have been found in which two studies
Frohlich and Hyde 1999; Frohlich et al 2000
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current estimates of global fungal diversity range from what to what
0.5mil to 10 mil
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Why may the early estimate of 1.5mil be a gross underestimate?
there were overlooked groups such as lichens and endophytes
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plants harbour numerous non-pathogenic fungi called what, in their tissues?
endophytes
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why is the ecological significance of endophytes uncertain
they appear to have no -ive impacts on plant function, although may provide plants w protection against insects and pathogens
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endophytes have been found in how many plants
all
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what suggests that the tropical endophytes may be extremely diverse
evidence of host preference and spatial heterogeneity
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how many endophytes did Aptroot 2001 find n a single Elaeocarpus tree in Papua New Guinea
200, incl many new spp.
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What are 5 mechanisms by which different fungi mediate the process of atmospheric/ biotic nutrient cycling
- N-fixation: autotrophic/ heterotrophic/ symbiotic.
- Trace gas emissions
- Denitrification
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the mechanisms photosynthesis, respiration, and decomposition, carried out by fungi, mediate which key ecosystem process
carbon cycling
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competition for nutrients by fungi contributes to which key ecosystem process
regulation of primary production
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how do fungi affect regulation of secondary consumers
- pathogenic agents- viruses and bacterial pathogens of insect, birds and reptiles
- predators- nematode trapping fungi, including wood-rotting basidiomycetes; slime moulds
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what mechanisms to fungi carry out to mediate the key ecosystem process of nutrient cycling
decomposition, nutrient mineralisation; mutualisms for nutrient uptake; leaching losses of N; nutrient immobilisation
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decomposition of wood (ligning and cellulose) depends on
fungi and bacteria
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saprophytic fungi incl. diverse range of ___ and ____________ spp
macro and microscopic
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what do the enzymes and acid compounds saprophytic fungi discrete do?
they degrade large molecular complexes into simple compounds
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there is usually a succession of species, ranging from those that colonise fresh material to those that do what
mop up afterwards
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saprotrophic fungi form extensive ____ and networks of aligned _____ that connect and _____ nutrients over several metres (Boddy 1993)
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what do some fungi use these cords as
raised webs that catch litter before it reaches the ground
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in tropical rainforests, these fungal hyphae networks influence what (Guevara and Romero 2004)
local availability of nutrients
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wood decay polypore fungi can also be what
aggressive pathogens that attack living plants, destroying roots/ cambial tissue and ultimately killing trees/ making them more susceptible to windthrow
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what do other polypore fungi do
colonise trees but dont spread until after tree death
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what have studies of Panamanian large wood-decay polypore fungi found
although the most abundant spp colonise multiple hosts, fungal diversity in this group still exceeds that of the host trees.
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the majority of plant pathogens are
fungi and oomycetes
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how do they disperse
airborne spores
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where are they particularly prevalent
understorey where conditions for germination prevail such as high humidity, surface moisture and cool temperatures
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what are the most familiar and what do they cause
foliar pathgoens- necrosis, chlorosis or leaf deformation
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what are damping off diseases
kill seeds and seedlings
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what else can pathogens do
cause cankers in stems that block plants' vascular systems, decay wood in trunks and roots and also attack flowers and developing fruits
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their collective impact on plant performance and survival may be as great as, or even greater than, herbivores. why
their ubiquity and impact on a no. of life history stages and plant parts
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what are the main causes of damping off disease
Phytophthora, Pythium oomycete spp
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what did augspurger 1983 and augsperger and kelly 1984 find on barro colorado island
That Phytophthora and Pythium oomycete spp infected 80% of examine spp and seedling mortality of Platypodium elegans ranged from 35-81%
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once considered fungi, what are oomycetes more closely related to?
photosynthetic algae such as diatoms and to the malaria parasite
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pathology and persistence of Phtyophthora cinnamoni, the best known example, which is a major crop pest, is enhanced by what
moist conditions
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what are also vulnerable to fungal diseases
seeds in soil bank
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According to Hood et al 2004, what percentage annual mortality does Miconia argentea suffer
47%
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seed and seedling pathogenic agents are believed to be key players in what
the density dependent processes that contribute to the maintenance of high species diversity in the tropics.
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foliar pathogenic fungi affect many larger plants but are rarely lethal and mainly do what?
reduce the photosynthetic capacity of leaves
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foliar pathogenic fungi are remarkably what
widespread and abundant
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what did barone 1998 find in Panama on 10 tree spp?
fungal pathogens accounted for 34% of leaf damage
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How many out of 21 tree spp examined in several other localities in Panama and Brazil were affected by foliar diseases (Gilber and Sousa 2002)
21
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While foliar pathogens appear ubiquitous across sites and seasons, there is considerable variation in the degree of infection among spp. the probability of infection appears to be related to what
herbivory
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leaf damage caused by herbivores does what
renders leaves more susceptible to attack by foliar pathogens
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Reduction in plant growth due to fungi can be substantial, as in the case of the tree Erythrochiton gymnanthus in Costa Rica, which suffered what reduction in its growth rate due to an infection by the petiolar pathogen Phylloporia chrysita?
52% (Esquivel and Carranza 1996)
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many tropical forest insects are affect by what fungi
entomopathogenic fungi
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neotropical forest spores may contain as many as _____-_______ spores g-1 of Metarhizium anisopliae which infects various insects including leafcutter ants
1000-50000
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the large majority of ants remain uninfected despite the high exposure of leafcutter ants to pathogenic fungi, why is this
regular self grooming and secretion of antibiotics
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fungal spores that germinate and penetrate the host cuticle ultimately kill the insect when the fungus what
sporulates
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entomopathogens often bring about weird behavioural changes in their hosts like dying animals climbing as high as possible, why do they do this?
so fungal spores spread more widely
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What does the Cordyceps genera do once the mycelium has invaded the host
develop a club shaped organ containing fungal spores which is supported on the end of a stalk which may be as much as 10cm in length
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What are the Laboulbeniales?
minute ascomycetous fungi, obligately associated with arthropods, mostly insects.
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One genus of Laboulbeniales is Rickia, which has approx 145 spp. what is the host range?
encompasses distantly related arthropods such as mites, millipedes, mole crickets, ants and various beetles.
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What do the Rickia fungi do?
attach to arthropod cuticles through which they absorb nutrients, although this appears to have little consequence for the host.
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A study in North Sulawesi on Laboulbeniales collected from beetles indicates what? (Weir and Hammond 1997)
tropical diversity may be high because host species are numerous and parasites appear host specific.
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Vega and Dowd 2005 found that fungi are essential to the what of many insects
digestive processes
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What did Suh et al 2005 find when looking at digestive tracts of tropical beetles?
650 yeasts
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