Module 6 - Microbes in the Environment Flashcards
Define autotrophic respiration
CO2 flux (rate) that is strongly influenced by recently photosynthesised carbon from plants (e.g., root respiration, root-associated microbial respiration)
Define heterotrophic respiration
CO2 flux (rate) that is strongly influenced by decomposition of older carbon such as organic matter (e.g., many free-living organisms)
What are the two main pathways of carbon into soils (and which of these involves more labile carbon)?
Litter (e.g, dead shoots, roots, symbionts)
EXUDATES (active carbon via live roots and mycorrhizal fungi) -> more labile carbon, faster pathway
What have large-scale forest girdling experiments shown about photosynthesis and soil respiration?
That Current Photosynthesis largely drives soil respiration (~50% less CO2 released from soil when trees have been girdled)
Define Priming
An increase in degradation of native (often recalcitrant) carbon, because of inputs of labile carbon
What is the difference between the degradation caused by White Rot fungi vs Brown Rot?
Brown Rot: degrades cellulose -> lignin
White Rot: degrades lignin -> cellulose
Name 3 examples from the suite of enzymes required to break down complex molecules such as cellulose
Endoglucanase, Exoglucanase, Cellubiase
Name 3 monomers that make up lignin
p-coumaryl alcohol; coniferyl alcohol; sinapyl alcohol
Name the two enzymes found in White Rot fungi which can transfer electrons from H2O2 to lignin
Lignin peroxidase or manganese peroxidase
Name the non-peroxidase enzyme which is found in White Rot fungi, and what it does
Laccase - directly oxidises lignin (demethylation)
What happens to increase the rate of lignin breakdown when White Rot fungi start to degrade it?
Uncontrolled chain reaction splits open ring structures
What are the three (mentioned) examples of important symbioses?
Lichens, Nitrogen-Fixing Bacteria and Mycorrhizal Fungi
What are the two components of lichen?
Mycobiont (fungus) and Photobiont (algae or cyanobacteria)
What do the two components of lichen each contribute?
Alga provides sugars via photosynthesis; fungus protects alga from dessication
What is noticeable about where lichen grow (2 things)?
They are tolerant of extremes (pioneer colonisers on rock faces etc) and SOME are sensitive to air pollution - bioindicators
What is the name of the family of plants that can fix nitrogen?
Fabaceae
How does nitrogen fixation occur in Fabaceae?
Due to mutualistic bacteria (alpha- and beta-proteobacteria) that colonise Fabaceae roots; catalysed by the enzyme nitrogenase
How do plants prevent “cheating” by some bacteria, when multiple species colonise a plant?
They control oxygen supply to nodules to “reward” co-operative bacteria
What are Mycorrhizas?
A mutualistic association between plant roots and soil fungi [based on transfer of soil derived nutrients, N + P, to the plant, and reciprocal transfer of photosynthate (carbon) to the fungus]
What is the defining feature of Arbuscular Mycorrhizal Fungi?
Arbuscules - the site of nutrient exchange (between plant and fungus) within the root
What is the other feature of arbuscular mycorhizzas besides arbuscules?
The Extra-Radical (or external/extramatrical mycelium) -> grows beyond roots into soils and forms extensive networks to facilitate nutrient and water uptake
Which types of plants are the most common ectomycorrhizal host plants?
Woody, perennial plants
What are the effects of increased Arbuscular Mycorrhizal diversity on plants?
Increased shoot biomass, root biomass, hyphal length and phosphorus content of plants
What “dogma” of inorganic nutrient use by plants, has been challenged recently?
That plants can only take up inorganic forms, and rely on free living microbes to convert organic forms with enzymes;
It is possible that plants, aided by Mycorrhizal Fungi, could also mineralise or take up simple organic forms directly
Name the species of parasitic fungus that mainly infects ants?
Cordyceps sp.
What three types of relationship are technically considered to be “symbiosis”?
Mutualism, Commensalism and Parasitism
What does Cordyceps sp. do once it has infected an insect?
It causes the host to move to an area where conditions are optimal for fungal spore dispersal, then the host dies.
Describe what is meant by “fungal gardeners”
Some ants “harvest” particular genotypes of fungi so they can use the substrates that the fungus breaks down
Some also harvest bacteria that produce antibiotics to reduce competition for the “farmed” fungus
Name a species of nematophagous fungi
Drechslerella sp.
In what kind of soil are nematophagous fungi usually found?
Nitrogen-deficient
What animal species do some Ectomycorhizzal Fungi (EMF) predate?
Springtails (Collembola)
What effect did the presence/absence of Collembola have on CO2 release from soils with AMF?
CO2 release was LOWER when Collembola were present - “Collembola reduce flux of recent plant assimilate from Mycorrhizal Fungal networks”
What is meant by PSF?
Plant soil feedback - plants have an effect on both their biotic and abiotic community, which can effect subsequent generations of plants
What is the common plant response to aphid attacks?
Plants release Volatile Oxygen Compounds (VOCs) which are repellant to aphids and attractive to aphid predators (e.g., wasps)
Is the increased attractiveness to aphids when plant roots are colonised by AMF due to increased Phosphorus?
NO - adding AMF increased aphid attractiveness, but adding P did NOT. “Must be something else”
What is believed to be the reason that AMF presence affects plant attractiveness to aphids?
Hyphal network signalling
What is the benefit to the fungus of hyphal network signalling to repel aphids?
The fungus benefits from a good carbon source from all the plants in the network
Name the three main families of plants (mentioned) that are involved in ectomycorrhizae
Pinaceae, Dipterocarpaceae and Fagaceae
