Lecture 19: Ecosystems: Phosphorus cycle, terrestrial nutrient regeneration Flashcards
what element is essential as building blocks of amino acids, for building proteins, and DNA
nitrogen
Nitrogen exists in ____________________
many oxidized and reduced forms
Most nitrogen is found in the atmosphere (N2), which is _____________________________ — availability of usable nitrogen is often ______________
- not a useable form for organisms
- limiting for growth
Most useable nitrogen in biological systems originates from the process of _______________
nitrogen fixation
Five major steps in the nitrogen cycle
- Nitrogen fixation
- Nitrification
- Assimilation.
- Mineralization
- Denitrification
Five major steps in the nitrogen cycle - nitrogen fixation
Conversion of atmospheric nitrogen into forms producers can use
five major steps in the nitrogen cycle - Nitrification
The conversion by bacteria of unusable, excreted forms of organic nitrogen (ammonia) back into forms that can be used by producers (think of this as organic recycling).
five major steps in the nitrogen cycle - Assimilation
Conversion of useable forms of nitrogen into plant/producer tissue
five major steps in the nitrogen cycle - Mineralization
Breakdown of biological nitrogen into inorganic forms (e.g. ammonia)
five major steps in the nitrogen cycle - denitrification
The breakdown of organic nitrogen in the absence of oxygen, resulting in the release of molecular nitrogen back to the atmosphere
how is some nitrogen fixation driven by lightning strikes
lightning contains enough energy to convert Nitrogen gas into Nitrates that plants can use
Most biotic nitrogen fixation achieved by what three groups of bacteria
- Cyanobacteria
- Azotobacter
- Rhizobium
what are Cyanobacteria
free-living autotrophs
what are Azotobacter
free living soil microbe
what are Rhizobium
it forms symbiotic relationships with the roots of some plants
Which major group of plants has rhizobium?
legume (pea family) plants
rhizobium on legume plants
- Reaction requires limited oxygen
- Nodules provide very stable, low oxygen conditions
- Nitrogen gas used to make ammonium compounds.
- These compounds are absorbed by plants.
Phosphorus is a major component of what
- nucleic acids
- cell membranes
- energy transfer systems
- bones
- teeth.
The phosphorus cycle is __________ than the nitrogen cycle, because phosphorus is ______________ (no gas phase) and does not readily undergo oxidation and reduction.
- simpler
- bound to the land and water
_____________ result directly from ____________ of rocks.
- Phosphate ions
- weathering
_______________________ phosphorus in the form of ____________________.
- Plants assimilate
- phosphate ions
_____________ are taken up from __________ and used directly in organic molecules
- Phosphate ions
- water and soil
Excess phosphorus in the diet of organisms is also ________________________, making it readily available again.
excreted as phosphate ions
how is the phosphorous cycle different than the nitrogen cycle
there are no complex transitional and unusable forms in the Phosphorus cycle
____________ significantly impact phosphorus availability
Acidity levels
In _____________________________ conditions, phosphate ions bond tightly to other elements to form ______________ - including calcium, leading to _____________________ in aquatic systems
- moderately strong acidic and basic
- insoluble molecules
- precipitation and storage
The well oxygenated surface waters of aquatic systems can experience _______________________ in the warm summer months because of the ___________________________________________.
- reduced productivity
- elevated rates of phosphorus precipitation
Human activities have approximately _______________ the amount of nitrogen going into terrestrial systems.
doubled
Sources of human nitrogen inputs
- Fertilizer production and use
- Nitric oxide from fossil fuel burning
- Planting nitrogen fixing crops on large scales
Fertilizers also used extensively to __________________
elevate phosphorous levels
Natural systems have ___________________________________
evolved under nitrogen and phosphorus limitation
________________ not used by crops ________ to natural systems and ___________________________ in those systems
- Excess nutrients
- transfer
- destabilize primary production
define Cultural eutrophication
Excessive increase in productivity in an aquatic system due to human activity
The ____________________________________ feed algae that bloom (unnatural population density) and cloud the water.
nitrogen and phosphorus runoff from fertilizers and detergents
Decomposition of the dying algae from the bloom significantly reduces dissolved oxygen — ________________
respiration of the decomposers.
_____________ creates ______________ with too little oxygen for multicellular marine life like fish, crabs, etc.
- Reduced oxygen
- uninhabitable zones
eutrophication results in __________________ with large, continuous aquatic systems.
aquatic “dead zones”
explain the distribution of aquatic and marine dead zones world wide
- coastal
- near lands with lots of people
In the bay, ____________________ , fed by the naturally high nutrient levels of an estuary system, function as the primary producers for a _________________.
- healthy algae populations
- rich and stable food web
More people upstream of the Chesapeake bay means ________________________ (fertilizers and sewage)
less natural land cover filtering and abnormally high nutrient inputs
less natural land cover filtering and abnormally high nutrient inputs results in a ________________________, with over-abundant primary producers driving ______________ that heavily impacts higher trophic levels.
- destabilized food web
- eutrophication
Oysters are critical ______________ in estuarine systems, filtering up to 50 gallons of water per day, and consuming filtered plankton and other organic particles.
primary consumers
result of oyster filtering
positively impact water clarity (with cascading benefits), and reduce algae abundance
uptake by plants & decomposition by microorganisms are sensitive to what
temperature, moisture, and pH
Plant uptake of nutrients typically has the capacity to be faster than the regeneration rate within an ecosystem, or the inputs from outside — ________________________
resulting in nutrient limitations on growth.
______________ is the ________________ in nutrient regeneration _______________________________ — the brown food web limits the green food web.
- Decomposition
- limiting step
- within terrestrial ecosystems
Decomposition (release of nutrients) occurs via 4 processes:
- Water leaching soluble minerals and organic compounds.
- Consumption by large detritivores.
- Breakdown of woody components by fungi.
- Bacteria finishing off the rest.
Fungi break down components of the detritus that ________________________
cannot be broken down by other processes
Saprotrophic fungi
The groups of fungi that are involved in detritus decomposition
what are Fungal hyphae
- threadlike network of growing and feeding
structures - penetrate plant and wood material bacteria cannot reach
what is lignin
gives wood its key “woody” properties
what can break down lignin
it can only be broken down by a class of fungi known as the white rot fungi
Fungi release __________that break down surrounding material, then they __________ the resulting sugars and amino acids.
- enzymes
- absorb
what improves nutrient uptake by terrestrial plants.
Mycorrhizal associations between fungi and plant roots
two major forms of mycorrhizal
- Arbuscular mycorrhizae
- Ectomycorrhizae
define arbuscular mycorrhizae
- fungi penetrate the cell walls in root tissue and form branching vessels in close contact with root cell membranes
- common in herbaceous plants, including many crops.
define ectomycorrhizae
- Form a dense coating around the outside of small roots and penetrate the spaces between cells in the outer layer of the root
- common in woody plants
Mycorrhizae are _____________________, but are particularly __________ for plant uptake in systems with __________________
- found in all ecosystems
- valuable
- nutrient poor soils
Mycorrhizae help most in the __________________, like phosphorus - key limiting nutrient.
uptake of less soluble nutrients
Mycorrhizae penetrate more soil area than the original root structure is capable of, ________________ for nutrient assimilation
increasing surface area
The _________ secreted by the mycorrhizae further improve the ______________________.
- enzymes
- extraction of nutrients
Mycorrhizae, and especially ectomycorrhizae, can help ____________ by physically excluding pathogens or _____________
- prevent disease
- producing antibiotics
