Final Study Guide - Biogeochemistry Flashcards
Why is decomposition so important?
It turns organic materials from identifiable plant, animal, and microbial residues into CO2, inorganic nutrients, and humus.
What large-scale ecosystem processes are supported by decomposition?
Decomposition is essential for:
(1) nutrient cycling, (2) ecosystem functioning, regulation of the accumulation of (3) organic matter and regulation of (4) atmospheric composition
What groups of soil biota have a direct and indirect role on decomposition?
Direct: microorganisms
Indirect: microfauna, mesofauna, macrofauna
Do microorganisms have a direct role on decomposition? How?
Yes, because they partake in biochemical decomposition
Do earthworms have an indirect role on decomposition? How?
Yes. They do this by breaking down the soil and being soil engineers
What are the steps in biochemical decomposition of organic compounds? What type of enzymes catalyze these steps?
First organic compounds are broken down into simpler molecules (catabolism). Then they are converted to inorganic forms (mineralization)
Extracellular and intracellular enzymes catalyze these steps, respectively
How does the particle size, recalcitrance, molecular complexity and C:N ratio drive the decomposition of an organic waste?
Smaller size = faster decomposition
Higher recalcitrance (molecular complexity) = slower decomposition
High C:N ratio: slower decomposition
High C:N ratio leads to slower decomposition because organisms take up C/N in proportions equal to their own biomass
What is a recalcitrant compound? What is the opposite concept of recalcitrance?
A recalcitrant compound is resistant to degradation. The opposite concept is lability, which refers to a substance that can be easily broken down
Which compound is more recalcitrant? Glucose or lignin?
Lignin is more recalcitrant (it is a more complex molecule)
In the process of decomposition who takes care of the breakdown of the more labile compounds? Bacteria or fungi?
Bacteria takes care of more labile compounds whereas fungi take care of more recalcitrant compounds
How does the composition of the microbial community change through the process of decomposition?
It looks like a bell curve that is low at first, increases to a peak, then decreases back to the original
See the biogeochemistry soil C lecture week 8 slide 22
Will a residue with C:N ratio result in immobilization of N? why?
When organic material with a high C:N ratio is added to the soil, microbes will cause N immobilization
What range of pH do bacteria and fungi prefer to carry out decomposition?
Bacteria: 6.5-8 pH
Fungi: 5.5-6.5 pH
Does oxygen concentration in soil accelerate or slow down decomposition? Why?
It accelerates decomposition because the aerobic organisms that carry out most of the decomposition in soil need oxygen
Are texture and structure important for decomposition? Why?
Yes, because they affect the air and water content in soil which is important for decomposition
In which soil ecosystem are decomposition rates higher, in a boreal bog in Canada or in a tomato cropping soil in California? Why?
The tomato cropping soil, because it has warmer temps, are more aerated, and have more labile organic compounds
Which soil horizon is more enriched (has higher concentration) of organic matter?
The O horizon
How did soil C contribute to the failure of the Biosphere 2 experiment?
There was too much organic matter in soil that was decomposed, leading to high CO2 production
How does soil C become chemically/biochemically or physically stabilized?
Chemical stabilization: flocculation
Physical stabilization: organic molecules become concealed or covered by mineral particles in soil aggregates
What is microbial necromass and how does it contribute to C stabilization?
Dead microbes. Contributes to C stabilization because it is sticky and binds to soil particles, protecting it from microbial degradation
How many different forms of N can be found in soil?
9 different forms
Arrange the forms of N from less to more oxidized
Least to most oxidized:
Soil organic N (R-NH3), ammonium (NH4+), ammonia (NH3), hydroxilamine (NH2OH), nitrogen gas (N2), nitrous oxide (N2O), nitric oxide (NO), nitrite (NO2-), nitrogen dioxide (NO2), nitrate (NO3-)
What is the most abundant form of N in soils?
Soil organic N
What are the two forms of plant available N in soils?
Nitrate (NO3-) and ammonium (NH4+)
