decomposition

Question 1

what is decomp

Answer 1

the physical and chemical breakdown of detritus into CO2 and inorganic
nutrients through chemical alteration, leaching and fragmentation

Question 2

what does decomp balance

Answer 2

balance between primary production and decomposition strongly
influences carbon and nutrient cycling (no cycle, if no recycling
through decomposers)

Question 3

what happens if no decomp? ex?

Answer 3

Detritus accumulation, the lack of availability of nutrients that are readily available and the
depletion of atmospheric carbon dioxide
Massive accumulation of cattle dung because dung beetle was evolved to using native
marsupials.

Question 4

what three processes does decomp involve?

Answer 4

1. Leaching by water
2. Fragmentation
3. Chemical alterations

Question 5

Describe leaching by water

Answer 5

Mineral ions and soluble materials transported through soil, away from
decomposing OM
- Most important early in decomposition
- Pulsing by solubilization of decomposition

Question 6

describe fragmentation

Answer 6

Fragmentation – physically breaking own the matter
- Freeze and thaw cycles
- Wet and dry cycles
- Surface area and volume such that as you break it down OM, surface
are gets larger compared to volume thus changes how minerals react
with ions in soil

Question 7

what is impacted by break down of OM/SA

Answer 7

Photosynthesis - lower surface area to volume more allocation to
biomass of photosynthetic structures
- breaking down OM into smaller matter through fragmentation
increases surface area to volume ratio
- Soil texture -

Question 8

describe chemical alteration

Answer 8

Changes chemical composition of detritus
- Primarily from microbes (bacteria and fungi)
- Less usable (organic) à usable (inorganic) forms
- Mineralization – the conversion of carbon and nutrients from organic
to inorganic

Question 9

microbes? what do they do?

Answer 9

bacteria (animal material) and fungi (plant material) = microbes
- Secrete enzymes specialized to the niche to breakdown litter macromolecules into inorganic
forms to contribute to gross mineralization

Question 10

what accounts for most decomp in aerobic environments

Answer 10

fungi

Question 11

describe fungi

Answer 11

Intolerant to low O2 (if water is saturated there isn’t room)
- Secrete enzymes that penetrate plant cuticles and cell walls (lignin, cellulose,
hemicellulose)

Question 12

How do fungi differ from bacterial

Answer 12

• Differentiates from bacteria because they have hyphal networks – allows them to import
  and transfer nutrient over long distances
• Tolerant lower availability of nutrients in a place due to transportation,
• Adapted to processing ligand and cellulose which are hard molecules hard to
  break down

Question 13

describe bacteria

Answer 13

-Specialized on labile substrates (animals)
- Tolerate low oxygen
- Differentiates from fungi such that they can continue processes under waterlog
conditions and low oxygen (Example: extreme soil compaction)

Question 14

role of protozoans

Answer 14

• Predators of bacteria

Question 15

role of nematodes

Answer 15

Predators of bacteria, fungi and also root herbivores (invertebrates)

Question 16

describe mesofauna- two common types?

Answer 16

Taxonomically diverse
- Most common:
a) Springtails (Collembola): small insects that feed on fungi
b) Mites (Acari): trophically diverse, consume decomposing litter, predators of bacteria and
fungi

Question 17

describe macofauna

Answer 17

• Ecosystem engineers that alter soil physical properties (tunnels change the flow of water,
  change interactions between organisms)
  -Earthworms (temperate) or Termites (tropical)

Question 18

role of macrofauna

Answer 18

Fragment liter
-Alter soil structure
-Mix OM into the soil

Question 19

how is decomp rate calculated?

Answer 19

Decomposition = Lt = L0 * e-kt
L = litter loss

Question 20

decomp calc example

Answer 20

Lt= 30
Loe = 40
30/40 = e- k (12)
Ln (0.75)/12 = -k
-Ln (0.75)/12 = k
= 2.3% reduction per week

Question 21

what is k=? higher k means?

Answer 21

K = litterfall/litterpool/ decomp constant
Higher k = higher decomp
Lower littler pool , less OM on ground , decoop is being done fast

Question 22

how IS DECOMP measured as

Answer 22

Mass loss in litterbags
- Carbon dioxide release
- Mass balance (physical mass decomposition

Question 23

look at graph of litter loss

Answer 23

ok

Question 24

how does spatial variation in decomp work - soil surface

Answer 24

most decomp = soil surface
- litter inputs concentrated
- greater temporal variation in temp and moisture and decomp rates
- principally by fungi (aerobic env)

Question 25

how does spatial variation in decomp work- mineral soil

Answer 25

temp + moisture more stable (and decomp rates)
- rhizosphere = major zone of decomp; high inputs of C (root exudates)
-supports microbial activity
- lower O2

Question 26

what controls decomp rates (K)

Answer 26

1. Physical Environment
   2.characteristics of soil community
2. Substrate or litter quality

Question 27

how does physical environment control decomp

Answer 27

indirect effects
Temperature increases microbial activity thus decomp but can cause
decreases in soil moisture and decomp in some cases

Question 28

how does temp increase decomp

Answer 28

increase temp = microbial activity = increase soil respiration
- Adapted to temperature it is typically found in (once at optimal it
declines decomp rate)
- Increases temperature = increase evaporation = decreases water availability = increases oxygen availability
increase temperature = increase weather = increases nutrient availability = increases microbial activity = increases soil respiration

Question 29

when does moisture increase decomp

Answer 29

if sufficient O2 available

Question 30

how does soil properties affect decomp

Answer 30

clay = lower decop (binding of enzymes, help breakdown OM) - decome usually lower in acidic soils (fungi intolerant)

Question 31

how does substrate/litter quality affect decomp

Answer 31

substrate quality – how easily broken down (labile) -> predom control on decomp

animals> deciduous leaves> evergreen leaves> wood
ratio of lignin to N

Question 32

lignin impact on decomp

Answer 32

ratio of lignin: nitrogen – in litter often a good predictor of decomposition
Higher k = higher decomp rate
Higher lignin:N ratio = lower decomp rate
More nitrogen available = lower rate of decomp b/c plants don’t need to extract it from the
soil

Question 33

how does lignin ratio differ by biome?

Answer 33

structures in coniferous have higher lignin to nitrogen ratio thus have lower rates of
decomposition compared to deciduous which has less structurally enforced material, soft
tissues thus the rate of decomposition is high

Question 34

what is left in humus by end of decomp

Answer 34

primarily recalcitrant items (lignin, chitin, microbial cell walls)

Question 35

What is the relationship between NPP and decomposition?

Answer 35

Increases NPP, there is increased plant material for decomposition thus increase in
decomposition

Question 36

why does increased NPP mean an increase in Decomp

Answer 36

increases NPP = decrease amount of structural investment and increase in leaf investment

Question 37

why is NPP increased by decomp

Answer 37

Rate of respiration by bacteria decreased =
Increase n = reduced rate of respire
b/c increased n , plants don’t have as many myhroziall relationship thus reduced fungi in soil

therefore overall rate of respiration is lower
more n = plant don’t produce exudates thus less microbial activity = less respiration, reduced mibroial biomass and eudates = reduced in liginal enzymes which are needed to break
down OM