Decomposition 2

Is decay partly influenced by plant biochemistry?

• yes

What is the difference in nutritional value in plants in terms of C:N ratio?

• Higher C:N ratio = poor nutritional quality

• Lower C:N = has a higher nutritrional value

How is C:N a measure of resistance?

• higher cn indicates more structiural and secondary compounds

Changes of cn for a substrate over time is an indicative of decay stage. What is the difference between the ratio from tissue transforming from plant material to humic material?

• 60-90 to 12-15

what are the three stages of the generalised model of microbial decomposition of OM?

• Complex polymers like cellulose get broken down by extracellular enzymes

• The breaking down chop and divides the complex polymers into monomeric units i.e sugars

• depends on aerobic and anerobic conditions for the products produced

In anaerobic conditions, where only some bacteria and archaea survive, what products are produced?

• co2

• methane

• alcohols

• less energy and biomass

In aerobic conditions, what products are made by bacteria, archaea and non filamentous fungi?

• co2

• water

• more energy

• more biomass

What is the link between community and decomposition?

• in order for efficient decomposition to occur, there is a requirement for the collaberation of a mixed species community to break things down

• fungi deal with large compounds

• bacteria deal with the small stuff!

what does it mean by co metabolism?

• microbes use energy from a more labile C source to partially degrade a more complex one

What is the primary effect?

• input of more labile organic matter stimulates or accelerates the decomposition of more complex material

why is lignin difficult to decompose?

• large macromolecule

• poorly soluble

• random structure

• requires non specific enxymes to break down the non hydrolysable bonds

• encased in crystalline cellulose matrix

is lignin degradation an example of co metabolism?

yes

How do the non specific enzyme breakdown lignin?

create hydroxide free radicals which bombard lignin

Which other structural polysaccharides deem more diffucult to break down?

• cellulose

• pectin

what are the 5 main environmental controls on decomposition?

• temperatire

• moisture and redox potential

• organic matter quality

• soil physical and chemical properties

• decomposer community and fauna

what are modulatig and indirect factors that affect decomposition?

• seasonality like shifts in climate and conditions

• vertical position : temperature, moisture, o2 and resources are stratified with depth

• topography and aspect - alter local hydrology and temperature

How does soil warming affect microbial community composition?

Reduced moisture and available substrates favour K-strategists over R-strategists.

what is the role of rhizosphere in soil decomposition?

• root exudates feed microbes

• this supports microbial growh

• priming and increased co2 release

what does girdling demonstrate about soil respiration?

It blocks sugars reaching roots, reducing root respiration and exudate-fed microbial activity; the CO₂ decrease helps separate respiration sources.