decomposition Flashcards
what is decomp
the physical and chemical breakdown of detritus into CO2 and inorganic
nutrients through chemical alteration, leaching and fragmentation
what does decomp balance
balance between primary production and decomposition strongly
influences carbon and nutrient cycling (no cycle, if no recycling
through decomposers)
what happens if no decomp? ex?
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.
what three processes does decomp involve?
- Leaching by water
- Fragmentation
- Chemical alterations
Describe leaching by water
Mineral ions and soluble materials transported through soil, away from
decomposing OM
- Most important early in decomposition
- Pulsing by solubilization of decomposition
describe fragmentation
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
what is impacted by break down of OM/SA
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 -
describe chemical alteration
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
microbes? what do they do?
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
what accounts for most decomp in aerobic environments
fungi
describe fungi
Intolerant to low O2 (if water is saturated there isn’t room)
- Secrete enzymes that penetrate plant cuticles and cell walls (lignin, cellulose,
hemicellulose)
How do fungi differ from bacterial
- 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
describe bacteria
-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)
role of protozoans
- Predators of bacteria
role of nematodes
Predators of bacteria, fungi and also root herbivores (invertebrates)
describe mesofauna- two common types?
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
describe macofauna
- Ecosystem engineers that alter soil physical properties (tunnels change the flow of water,
change interactions between organisms)
-Earthworms (temperate) or Termites (tropical)
role of macrofauna
Fragment liter
-Alter soil structure
-Mix OM into the soil
how is decomp rate calculated?
Decomposition = Lt = L0 * e-kt
L = litter loss
decomp calc example
Lt= 30
Loe = 40
30/40 = e- k (12)
Ln (0.75)/12 = -k
-Ln (0.75)/12 = k
= 2.3% reduction per week
what is k=? higher k means?
K = litterfall/litterpool/ decomp constant
Higher k = higher decomp
Lower littler pool , less OM on ground , decoop is being done fast
how IS DECOMP measured as
Mass loss in litterbags
- Carbon dioxide release
- Mass balance (physical mass decomposition
look at graph of litter loss
ok
how does spatial variation in decomp work - soil surface
most decomp = soil surface
- litter inputs concentrated
- greater temporal variation in temp and moisture and decomp rates
- principally by fungi (aerobic env)
how does spatial variation in decomp work- mineral soil
temp + moisture more stable (and decomp rates)
- rhizosphere = major zone of decomp; high inputs of C (root exudates)
-supports microbial activity
- lower O2
what controls decomp rates (K)
- Physical Environment
2.characteristics of soil community - Substrate or litter quality
how does physical environment control decomp
indirect effects
Temperature increases microbial activity thus decomp but can cause
decreases in soil moisture and decomp in some cases
how does temp increase decomp
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
when does moisture increase decomp
if sufficient O2 available
how does soil properties affect decomp
clay = lower decop (binding of enzymes, help breakdown OM) - decome usually lower in acidic soils (fungi intolerant)
how does substrate/litter quality affect decomp
substrate quality – how easily broken down (labile) -> predom control on decomp
animals> deciduous leaves> evergreen leaves> wood
ratio of lignin to N
lignin impact on decomp
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
how does lignin ratio differ by biome?
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
what is left in humus by end of decomp
primarily recalcitrant items (lignin, chitin, microbial cell walls)
What is the relationship between NPP and decomposition?
Increases NPP, there is increased plant material for decomposition thus increase in
decomposition
why does increased NPP mean an increase in Decomp
increases NPP = decrease amount of structural investment and increase in leaf investment
why is NPP increased by decomp
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
