Chapter 22: Decomposition and Nutrient Cycling Flashcards
1
Q
Primary production depends on the up take of what by?
A
- essential mineral nutrients by plants
2
Q
What is the original source of mineral nutrients for plants to up take?
A
- Atmosphere (carbon) or weathering of rocks and minerals (N, P, K, Ca, Mg, S etc)
3
Q
What happens to the nutrients once in the food chain?
A
- a lot of them get tied up…you have lots of nutrients but they get locked up in biomass until they are released via decomposition
4
Q
What is a large proportion of total nutrient pool in most ecosystems?
A
- nutrients in living tissues
5
Q
Nutrients in dead organic matter are mineralized by?
A
microbial decomposers
6
Q
Once nutrients in dead organic matter are mineralized by microbial decomposers what can happen?
A
- they can be taken up and incorporated by plants again via internal cycling
7
Q
Give a generalized model of nutrient cycling in a terrestrial ecosystem!
A
- NPP
- retranslocation via litter fall of leaves
- dead organic matter accumulates on forest floor
- decomposition/mineralization of organic matter
- yields soil nutrients
- these are taken up by plant
- incorporated into plant tissues
- NPP again
8
Q
What is up with decomposition?
A
- key process in recycling of nutrients within ecosystems
- results in release of energy and conversion of organic compounds into inorganic nutrients
- decomposers deed on dead organic matter or detritus
9
Q
What are microbial decomposers?
A
- bacteria, particularly for dead animal matter
- fungi, particularly for cellulose plant matter
- they secrete enzymes that break down compounds. Some products absorbed as food (we eat mushrooms)
- succession of microflora (theres a change in communities over time, maybe other things move in after another had broken down the material a bit )
- decomposers are eating by microbivores
10
Q
Detritivores?
A
- animals that feed on dead material (including dung)
- result in fragmentation of dead organic matter (detritus )
- characterized by body with
- fragmentation helps decomposition - better to break signs up not pieces and it break down easier
11
Q
Rate of decomposition is related to?
A
- quality of plant litter as substrate for decomposers : types and quantities of carbon compounds present
- Physical environment: soil properties (texture and pH) and climate (temperature and precipitation)
* moisture and temp are two big ones!
ex: ripe tmato will break down faster than a stick…lol
- warm and wet vs cool and dry
12
Q
Explain decomposition of spartina on exposure to air!
A
- hangs around a lot longer in anaerobic environment
- oxygen (aerobic) helps break down quicker
- of you want to enhance decomposition, bubble it
13
Q
Mineralization?
A
- during decomposition, microbial decomposers transform elements contained in organic compounds into inorganic forms
14
Q
Explain the mineralization example pertaining to the litter bag!
A
- litter bag C:N (50:1 - 100:1)
L> plant litter - consumption of plant litter as source of energy (carbon) and nutrients
- C:N (10:1 - 15:1)
fungi bacteria
L> CO2 loss from microbial respiration - mineralization: transform orgnaic compounds into mineral nutrients
- immobilization: uptake and assimilation of mineral nutrients by decomposers -> necessary to supplement the relatively low N content of plant litter!
- Net mineralization rate = mineralization rate = immobilization rate
15
Q
What affects rate of nutrient cycling?
A
- climate affects rate of primary production and decomposition and therefore rates of nutrient cycling (greater in warm, wetter climate)
- nature of organisms (life span, growth rate) also affects nutrient cycling e.g. plankton vs trees
- trees take long time to break down. Plankton recycle quickly (small - high surface area to volume ration in the water column to break down faster)
16
Q
____ determines rate of nutrient uptake.
A
- primary productivity
17
Q
___ determines rate of nutrient release.
A
- decomposition
18
Q
What occurs between nutrient uptake and release?
A
feedback between the two
**balance between PS and nutrient cycling when one stops the other does too
19
Q
Explain feedback in nutrient cycling in a low nutrient availability area!
A
-low nutrient availability –> low nutrient uptake –> low leaf nutrient concentration –> low net primary productivity–> low nutrient return to soil n litter –> low net mineralization rate –> low nutrient availability
20
Q
Explain feedback in nutrient cycling in a high nutrient availability area!
A
- high nutrient availability –> high nutrient up take –> high leaf nutrient concentration –> high net primary productivity –> high nutrient return it to soil in litter –> high net mineralization rate –> high nutrient availability
21
Q
Terrestrial vs Aquatic Ecosystems ?
A
- primary production an grazing vary between land and aquatic
- standing crop biomass on land accumulates and is stored
- blooms in the aquatic occur but it doesn’t accumulate in the water column
- vertical separation between sones of production and decomposition
- in terrestrial systems, plants bridge these two zones
- in aquatic environments, not always the case
- Terrestrial: Zone of primary production = canopy…Zone of decomposition = forest floor
- Aquatic: Zone of primary production = photic zone/ surface waters. Zone of decomposition = benthic zone/ bottom sediments
22
Q
Long term biological retention of nutrients in forests occurs where?
A
- stored in tree limbs, trunk, bark , roots and soil organic matter
23
Q
In aquatic environments, availability of nutrients depends on? Long term storage?
A
- turnover in phytoplankton and zooplankton
- deep bottom sediments
- aquatic has much more turnover …on land nutrients don’t really move a lot from where they were produced
24
Q
Open-water Ecosystems
- In deeper waters, primary production and decomposition locations? What is special about temperate and polar regions?
A
- In deeper water, separation between surface waters where primary production occurs and decomposition in bottom sediments
- in temperate and polar regions, this separation (thermocline) breaks down in fall and spring
- *nutrients sit on tourmaline (so dense - act as a barrier to primary production, nutrients can’t get to the bottom or back up until there is a turnover)
25
Q
Explain epilimnion, hypolimnion and thermocline with respect to turn over!
A
- in the summer the wind comes down hitting the epilimnion, thermocline is under it with nutrients and then hypolimnion
- warm, low density, low nutrient waters = epilimnion
- hypolimnion = cold, high density, high nutrient waters
- turn over occurs in fall and spring
26
Q
What is the relationship between availability of light.temp and nutrients?
A
- inverse
- NEED both lights and nutrients to have primary production taking off
- productivity is highest in between spring and summer ..very low in all other seasons
27
Q
Nutrients in streams and rivers?
A
- nutrient spiralling since nutrients are constantly being transported down stream
- some physical (wood detritus) and biological (uptake and storage in animals and plant tissue) retention
- strongly affected by inputs from adjacent terrestrial systems
- *nutrients NEED to be recycled and reused for primary production to occur. As nutrients move down the stream there is an opportunity to work on it.
28
Q
Explain the nutrient spiralling in streams and rivers!
A
- As the flow of water movies causing spirals :
- uptake: incorporation of mineral nutrients into biomass in water column
- turnover: decomposition and mineralization of nutrients in dead organic matter ..particulate component
29
Q
Costal ecosystems?
- impacted by?
- has what linking zones?
A
- impacted by terrestrial inputs and by currents
- has attached algae, like plants in terrestrial systems which link zones of decomposition and production
30
Q
Costal ecosystems:
- salt marshes are primarily what kind of system?
A
- detrital
31
Q
Costal ecosystems:
- what does Estuarine circulation result in?
A
- salt wedge of seawater on the bottom trapping sediment and nutrients
- freshwater flowing down and flowing the other way is seawater
- salt wedge - big chunk of seawater that comes up, gets less and less as it goes (great for nutrients)
32
Q
Surface ocean currents?
- global pattern of ocean surface currents affects?
- describe areas
A
- global pattern of ocean surface currents affects productivity and nutrient cycling
- in some areas, upwelling of cooler nutrient rich water from depth occurs. Can result in high productivity
33
Q
Terrestrial patterns in nutrient availability and use?
- much of the northern hemisphere has soils derived from?
- volcanic areas ?
- other parts of the world?
A
- much of the northern hemisphere has fertile soils derived from glacial till
- volcanic areas can have such soils
- other parts of the world have old , highly weathered and mostly infertile soils ex Australia, South America and India
34
Q
Nutrient poor areas?
- vegetation adaptations ?
- forest?
- humus layer?
A
- vegetation in nutrient poor areas has adapted and uses nutrients very efficiently
- forests productivity can be high
- large biomass n humus layer of soil
- layer of fine roots and humus critical for nutrient cycling and conservation
35
Q
Slash and burn agriculture?
- tropical rainforests?
- why do we do this?
- rotating crops importance?
A
- tropical forests are cut and burned to clear them
- when crops are planted, yields usually good in the first year but then decrease quickly afterwards. Bigger problem in tropical than in temperate areas.
- this occurs bc materials are used up. This is why you rotate your crops (say one plant uses a lot of phosphate, then you don’t want to just keep replanting it there)
36
Q
Describe why the rainforest is fragile!
L> is slash and burn good idea?
A
- most of the rainforests nutrients locked in its plants and animals
- harvesting trees, plants and animals removes valuable nutrients and can disrupt the nutrient recycling system within the rain forest
- topsoil shallow and held together by tree roots
- tree canopy scatters the power of heavy rainfall. Removal can cause erosion
- *Most of the nutrients in these areas are held up in plants NOT the soil so slash and burning would remove all the nutrients
37
Q
Rainforests:
- growth rate of trees?
- relationships ?
A
- trees grow very slowly here. Many trees don’t even bloom until 60 years old!
- most rainforest trees depend on complex relationship of animal pollinators and seed dispersers.
- changes that affect these animals affect the trees ability to recover
38
Q
How is the Rainforest is an intricate web?
A
- huge diversity of plants and animals but few individuals of each. Some found unrestricted areas.
- destruction of relatively small areas of rainforest can result in losses of many species
- A lot of specialists: complex interdependence among the niches and their inhabitants
- *they have thousands of species (very diverse) but there are only a few of each species. When you clear an area, you could wipe out several species (small populations). Lot of specialist species too! So they need the ecosystem to stay just as it is, not like species here (generalists) that can survive change
39
Q
Farming rainforests?
A
- 130,000km^2 a year of rainforest is destroyed
- cleared for large scale commercial plantations or livestock ranching and small farms and other uses
- rainforest soils are notoriously poor and generally cannot support human agriculture for more than a few years
- crops may grow well at first, mostly subsisting on the minerals released when reforest is brunt
- decomposition is slow bc nutrients are low in these areas
40
Q
Why are nutrients not recycled easily in rainforests?
A
- minerals are locked up in living plants and animals NOT the soil
- minerals wash away quickly without protection from forest canopy
- when there are few farmers, land can be left long enough to recover: sustainable on a small scale
- but when there are many farms/migrant farmers, large areas affected
- once it is cleared it takes A LONG ASS TIME to grow back
41
Q
Logging rainforests?
A
- they contain 50% of global standing timber
- take decades to reach economic size so it is not easy to harvest them in a sustainable manner
- logging road allow other commercial exploitation to follow e.g. access for farmers
- logging removes biomass, nutrients, effects the soil and on top of all this they put roads in to there (makes the ecosystem apathy creating more issues)
42
Q
What are other reasons the rainforests are cleared for?
A
- housing
- infrastructure: damns, roads, electrical and communication installations
- to extract minerals: mining for oil, gold and other minerals
- small scale gold prospectors use mercury to extract gold. Mercury is highly toxic and can seriously damage the ecosystem
- recreation activities: resorts
43
Q
Other effects of humans ?
A
- collection of wild animals and plants
- pollution of rivers
- fragmentation of rainforests destabilizes the forest interior (temperature and humidity
- fragmentation may prevent movement of individuals from one part of the forest to another
- fragmentation may reduce chance of reproduction if individuals live far apart
44
Q
Solutions to these issues with human activity in the rainforests? Slash and burn agriculture?
A
- alternatives to slash and burn program
- small scale farmers slash and burn because of poverty and lack of other land
- alternative cropping systems introduced: cover crops and fruit trees to reduce erosion, leguminous crops (nitrogen), alternative crops, diversification of crops
- initial investment needed (e.g. for improved seeds, better pasture management)
