Ecosystem Processes Flashcards
What are the 3 subsystems of an ecosystem?
The herbivore subsystem, the plant subsystem and the decomposer subsystem.
What % of NPP is above ground in forests?
10%
What % of above ground NPP in forest enters the herbivore subsystem?
5%
What % of NPP is above ground in grassland?
Up to 50%
What % of above ground NPP in grassland enters the herbivore subsystem?
25%
What makes up humin?
Soil components not soluble in alkali.
What makes up humic acids?
Soil components soluble in alkali and insoluble in acid.
What makes up fulvic acids?
Soil components soluble in alkali and soluble in acid.
Why is humus important?
Acts as a nutrients pool, maintains soil structure and provides water holding capacity.
What are the 4 main processes in decomposition?
Leaching + volatilisation.
Comminution.
Non-enzymatic chemicals.
Catabolism.
Define leaching.
Water passing through/over resources and the subsequent removal of nutrients.
Define volatilisation.
The evaporation of oils, waxes and resins. Only significant in certain plant matter.
Define comminution.
The breaking up of resources into smaller parts.
What are some examples of non-enzymic chemical processes?
Cellulose oxidation by sunlight.
Weakening of chain bonds by UV.
Degradation by weak acids.
What organisms perform catabolism?
1-15% is invertebrate based; the majority is microbial.
How can you estimate decay rate?
By measuring: weight loss, density change, O2 consumption, CO2 evolution etc.
What factors affect decay rate?
Temperature.
Water regime.
Actual evapotranspiration.
Resource quality.
How does temperature affect decay rate?
Higher temperatures result in higher decay rates but there is a ceiling.
How does water regime affect decay rate?
Highest decay rate occurs when the water regime is balanced.
How does resource quality affect decay rate?
Lignins + polyphenols inhibit enzyme activity. Phosphorus + nitrogen increase resource quality.
How does the C:nutrient ratio change as decay proceeds?
It changes to favour nutrients - CO2 is lost as decay proceeds.
How does nitrogen content inhibit decay?
High and low nitrogen content inhibit decay. High nitrogen content means microbes don’t need to decay as much litter.
When are nitrogen and phosphorus released during decay?
As a result of invertebrate grazing and mycelial antagonism (conflict between fungi).
What is the most oxidised form of carbon?
CO2
What is the most reduced form of carbon?
CH4
What is the most oxidised form of nitrogen?
NO3-
What is the most reduced form of nitrogen?
NH4+
Define annamox.
Oxidisation of ammonium to dinitrogen gas.
What are nitrogenases and where are they produced?
Enzymes produced by cyanobacteria that reduce nitrogen to ammonia.
What is the function of nitrate reductase?
To reduce NO3- to NO2-.
Define primary productivity.
Rate at which biomass is produced per unit area by plants.
Define gross primary productivity.
The total fixation of energy by photosynthesis.
Define autotrophic respiration.
The proportion of energy fixed by photosynthesis that is lost by respiration.
Define net primary productivity.
The difference between GPP and Ra - the actual rate of production of new biomass available for heterotrophic organisms.
What are the 2 opposing processes that drive the organic carbon cycle?
Photosynthesis and respiration.
Describe the latitudinal trend in primary productivity.
Higher latitudes have lower mean primary productivity. This somewhat reverses underground.
Define autochthonous organic matter.
Organic matter produced by photosynthesis within an ecosystem’s boundaries.
Define allochthonous organic matter.
Organic matter imported from outside the ecosystem.
What is the production/biomass ratio?
The rapidity with which living material can replace itself.
Define net ecosystem productivity.
The difference between GPP and total ecosystem respiration.
Give examples of factors that limit productivity.
Inefficient use of solar energy.
Water availability.
Temperature.
What is a constitutive plant defence?
A defence always present in the plant.
What is an induced plant defence?
A defence produced or mobilised to where a plant has been injured.
What is the carbon nutrient balance model (CNBM)?
The theory that the carbon-nutrient status of plants (determined by resource availability) controls the allocation of secondary metabolites.
What are feeding inhibitors?
Compounds in plants that control decomposition rate.
Define turnover time.
The period of time during which certain materials remain within a particular system.
