Midterm 2

Question 0

Define mineralization

Answer 0

A term refers to processes that release carbon as CO2 and other nutrients in inorganic forms. Mineralization involves mostly biotic processes.

Question 1

Define decomposition

Answer 1

general term for the breakdown of organic matter either from complex forms to simpler forms or from simpler forms to inorganic forms. Although decomposition may involves both biotic processes and abiotic processes, soil microorganisms do most of the work

Question 2

Define immobilization

Answer 2

refers to the accumulation of nutrients in soil microbial biomass resulted from microbial growth or assimilation

Question 3

Why are mineralization and decomposition linked to plant production?

Answer 3

Decomposition and mineralization are linked to plant production because most plants take up inorganic nitrogen only.

Question 4

How is litter decomposition correlated with lignin nitrogen ratio?

Answer 4

Litter decomposition rate is negatively correlated to initial lignin:nitrogen ratio

Question 5

What is soil respiration used as a measure for?

Answer 5

Solid organic matter decomposition

Question 6

What 5 transformations does nitrogen go through?

Answer 6

Nitrogen fixation: N2 —-> R-NH2 (or NH3,NH4+, NOx)

Ammonification: R-NH2 —-> NH3 (NH4+)

Assimilation: NO3 (NH4+) —-> R-NH2

Nitrification: NH4+ —-> NO2- —->NO3-

Denitrification: NO3- —-> NO2- —-> (NOx) —-> N2O—-> N2

Question 7

What’s the difference between phosphorous fixation and mobilization?

Answer 7

Fixation happens through a chemical process that makes phosphorous unavailable to plants.

Microbes play a crucial role in the transforming process from organic P to inorganic P, and in mobilizing chemically-fixed P (mycorrhizal roots and other rhizosphere activities).

Question 8

What’s the relationship between fire and nutrients?

Answer 8

While 10-50% of the N and S in plant canopy and litter can be lost from one fire event, ash and heat from fires can increase soil nutrient availability.

Fires can also cause large pulses of nutrient loss due to erosion from runoffs.

Question 9

What is denitrification?

Answer 9

Denitrification is a series of microbial processes starting from nitrate (NO3-) and ending with N2

Question 10

Name two requirements for denitrification.

Answer 10

Denitrification only occurs under anaerobic condition.

Denitrification needs reducing substrates as energy source.

Question 11

What does denitrification do to N in terms of atmosphere?

Answer 11

The enzyme system of denitrifiers is totally inhibited by free oxygen, but not ammonia. Denitrification is the process of returning reactive nitrogen back to the atmosphere

Question 12

When and how does sulfate reduction occur?

Answer 12

Sulfate reduction occurs at wide range of pH values, pressure, temperature and salinity. Sulfate reduction is inhibited by oxygen, nitrate, ferric (Fe3+) ions. H2S is very toxic to aerobes and plant roots.

Sulfate reduction is carried out by bacteria using organic substrates as reducing agents and sulfate as the electron acceptor

Question 13

What two processes balance net methane in the atmosphere?

Answer 13

Methanogenesis: Methanogenic bacteria require strictly anaerobic condition and redox potentials between -350 and -450 mV, or highly reducing environment

Methanotrophy: All methanotrophic bacteria require free oxygen for them to effectively oxidize methane

Question 14

What is biomethylation?

Answer 14

Microbial methylation of metals in the aquatic environment is an important process in biogeochemical cycling of metal ions, especially mercury. For methylation to occur, anaerobic condition and low pH are required

Question 15

What is humidity?

Answer 15

a measurement of water vapor content in the air, often expressed as water vapor pressure for absolute humidity. Whereas relative humidity is expressed as a percentage of saturation humidity at a particular temperature and pressure

Question 16

What is the dew point?

Answer 16

the juncture at which any further cooling results in the deposition of water vapor onto convenient surfaces, generally the very small atmospheric particles that serve as condensation nuclei

Question 17

What is an aquifer?

Answer 17

Rocks/regolith holding ground water

Question 18

What is an aquiclude?

Answer 18

Rocks that hold and transmit very little water

Question 19

What are 6 main influences in groundwater storage?

Answer 19

(1) the balance of precipitation and total loss from evapotranspiration; (2) vegetation and surface properties; (3) soil infiltration; (4) topography; (5) geology; and (6) human usage and disturbance

Question 20

What are the avg residence times for Mercury in atmosphere, soil, ocean, and oceanic sediments?

Answer 20

Average residence times for mercury in the atmosphere, soils, oceans, and oceanic sediments are approximately: 1 year, 1000 years, 3200 years, and 250 million years, respectivel

Question 21

How much sulfur do humans contribute to the budget?

Answer 21

24%

Question 22

What is the Redfield ratio?

Answer 22

His modified ratio of falling particles: C:N:P:Ca = 120:15:1:40, and for upwelling sea water: C:N:P:Ca = 80:15:1:3200

This relatively constant ratio represents the proportionality of most biological processes which link biogeochemical cycles at many levels in the ecological hierarchy from the cell level to the biosphere leve

Question 23

What is the relationship between sulfur oxidation and mining?

Answer 23

Oxidizing sulfur is the primary energy source for the microbial communities of the deep-sea hydrothermal vent ecosystem. Sulfur oxidation produce acid, so Thiobacillus thiooxidans and Thiobacillus ferrooxidans are used in mining

Question 24

What is the CLAW and has it played a role in climate regulation?

Answer 24

Negative feedback hypothesis: warmer seawater –> more DMS –> more aerosols –> more albedo –>cooling

However, no clear evidence so far indicates that this negative feedback has played a significant role in the global temperature regulation.

Question 25

Who performs nitrogen fixation and what enzyme do they use?

Answer 25

This reaction is performed exclusively by prokaryotes (the bacteria and related organisms), using an enzyme complex termed nitrogenase

Question 26

Nodule are formed on plant roots to host bacteria that can fix nitrogen in an oxygen free area by the use of which enzyme?

Answer 26

One means of protecting the enzyme from free O2 is the formation of leghemoglobin, which binds O2 to protect nitrogenase while making oxygen available for respiration in other parts of nodule tissue

Question 27

What is assimilation?

Answer 27

Nitrogen assimilation is the process in which inorganic nitrogen (NH4+ or NO3-) is converted into organic nitrogen forms

Question 28

What is ammonification?

Answer 28

Ammonification is the biological conversion from organic nitrogen to inorganic nitrogen–ammonium

Domestic animals and fertilizers contribute the most ammonia to the global budget

Question 29

What conditions does denitrification require?

Answer 29

1. Denitrifying microbes use NO3- or NO2- as electron acceptors.
2. Denitrification only occurs under anaerobic condition.
3. Denitrification needs reducing substrates as energy
4. The enzyme system is totally inhibited by free oxygen, but not ammonia.