EE.23

Question 1

what is often the most limiting nutrient for plant growth?

Answer 1

Nitrogen

Question 2

what are the two major pools of nitrogen and how do they differ in the amount of nitrogen they contain?

Answer 2

The atmosphere and soil+organisms are the two major pools of nitrogen, the atmosphere cotains 4x10^15t, which is about 4 magnitudes higher than soil and organism which contain

Question 3

How is nitrogen lost?

Answer 3

years of cultivation
increase in temperature
coversion to nitrate followed by leaching
fire - biomass combustion leads to a release of molecular nitrogen
to sediments

Question 4

where are the nitrogen sinks?

Answer 4

atmospheric molecular N2
denitrification in wetlands and aquatic ecosystems
storage in increased forest biomass
sediments
however a high turnover rate in liing tissues means that they have a low storage potential in equilibrium

Question 5

Nitrosococcus bacteria

Answer 5

oxdise ammonia to nitrite

Question 6

Nitrobacter bacteria

Answer 6

oxidise nitrie to nitrate

Question 7

what is the sole energy source of nitrifying bacteria?

Answer 7

oxidation - used for chemosynthetic assimilation of CO2

Question 8

Nitrification

Answer 8

oxidation by bacteria of ammonia to nitric acid in the soil

Question 9

Denitrification

Answer 9

when there is no oxygen present nitrate can act as an oxidising agent, as so itself become reduced to nitrite, for example some microbes reduce nitrate to nitrite, and others convert nitrite to ammonia. in low pH waterlogged soils some bacteria oxidise ammonium to free nitrogen

Question 10

give examples of bacteria which are able to fix nitrogen

Answer 10

Bacteria like Azotobacter & Clostridium
Nodulating bacterial Rhizobium
Blue-green algae Nostoc, Anabaena & Cylindrospermum
Actinomycetes like Frankia on tree roots

Question 11

explain the relationship between legumes and rhizobium

Answer 11

the plant pays the bacterium in carbohydrates in return for nitrogen fixation
if fertlizer is applied nodulating bacteria stops fixing nitrogen, and the plant stops feeding the bacteria
nitrogen fixations stops at pH below 4.0 in soils

Question 12

what percentage of soil is made up of nitrogen?

Answer 12

0.1 - 0.3%

however 97-98% is in a stable organic form as proteins or sugars

Question 13

what is retained in the soil for longer, nitrate or ammonia?

Answer 13

ammonia has a much longer retention time in soil, nitrate is quickly lost too leaching

Question 14

in deserts what fixes nitrogen?

Answer 14

lichens in the desert crust

Question 15

what are the sources of nitrogen pollution?

Answer 15

leaching of nitrates into ground water
Marine pollution from sewage and other terrestrial inputs
Globally widespread through atmospheric movement of gaseous ammonia

Question 16

what are the critical loads of nitrogen for soft water lakes and ombrotrophic mires in comparison to most terrestrial ecosystems?

Answer 16

Soft-water lakes and ombrotrophic mires have critical loads of 5 - 10 kg ha-1 yr-1
Most terrestrial ecosystems have critical loads of 15 - 20 kg ha-1 yr-1

Question 17

Sources of atmospheric nitrogen pollution

Answer 17

Industry
Vehicle exhausts
Farm animals
Fertilizer dusts
People eat only 10% of the nitrogen used in producing the food
ratios of fertilizer input to N in product are
3 wheat, 14 dairy and 21 meat

Question 18

why is the form of nitrogen input important?

Answer 18

Fertilizer inputs in the form of sodium nitrate are non-acidifying
Inputs in the form of ammonium sulphate are strongly acidifying
For every ammonium ion taken up by plants, a hydrogen ion is released into the soil

Question 19

explain the relationship between biomass and species richness

Answer 19

at lower biomass the species richness is greater

Question 20

explain the relationship between species richness and pH

Answer 20

as the pH decreases below 7.5 the species richness decline

Question 21

how does nitrogen deposition affect species richeness?

Answer 21

Nitrogen deposition reduces biodiversity

Question 22

how has human activity impacted upon nitrogen imput?

Answer 22

Approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing

Question 23

what affect on the environment has there been to large inputs of nitrogen from human activity?

Answer 23

Caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility

contributed substantially to the acidification of soils, streams, and lakes in several regions

Question 24

how has nitrogen imput from humans changes the carbon content in terrestrial ecosystems?

Answer 24

Increased the quantity of organic carbon stored within terrestrial ecosystems
resulting in losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen

Question 25

what is phosphorous required for?

Answer 25

Required for ADP/ATP production in membranes in nucleic acids

Question 26

what are the major phosphorous pools?

Answer 26

organic matter soluble and labile P P in minerals and occluded P

Question 27

how does the age of a soil affect is composition?

Answer 27

More highly weathered soils tend to be high in aluminium and iron This means phosphorus tends to get “locked up” Typically less than 1% of total soil P is available in older soils

Question 28

what are the bound forms of phosphorous?

Answer 28

``` Adsorbed P (attached to Al and Fe irons on the clay surface) Probably to some extent exchangable ``` ``` Occluded P (stuck inside clay particle) Probably “gone for all time” (or at least a very long time) ```

Question 29

where do you find highly weathered soils?

Answer 29

tropical rainforests

Question 30

are tropical rain forests phosphorous limited?

Answer 30

yes, research suggests that the concentration of phosphorous is a limiting factor in tropical rainforests

Question 31

how does [P] impact on photosynthesis?

Answer 31

increase in [P] in leaves correlates with an increase in leaf photosynthesis

Question 32

how does [P] impact on productivity?

Answer 32

higher [P] result in higher productivity

Question 33

what techniques do plants use to get P?

Answer 33

Organic acid exudation Mycorrhizae Special root forms (eg. proteoid roots)