EE Lecture 23: Nitrogen

Question 1

what is often the most limiting nutrient for plant growth

Answer 1

nitrogen -aas,proteins,enzymes

Question 2

give an example of how nitrogen is an essential part of many defensive chemicals

Answer 2

alkaloids

Question 3

what is formula for nitrateq

Answer 3

NO3-

Question 4

what is formula for nitrite

Answer 4

NO2- (has 2 i’s therefore 2 Os)

Question 5

what is formula for nitrous oxide

Answer 5

N20

Question 6

how many orders of magnitude difference between nitrogen pools? give examples of N pools

Answer 6

atm
soils and orgs
4 orders of magnitude difference

Question 7

outline some fluxes of Nitrogen

Answer 7

biomass
N uptake by roots
N excretion
Nitrification
Denitrification

Question 8

how/when is nitrogen lost

Answer 8

with years of cultivation
at increased temperatures
by conversion to nitrate followed by leaching
fire - biomass combustion
lost to sediments as well

Question 9

what does the high turnover of nitrogen in living tissues suggest about storage

Answer 9

high turnover of nitrogen in living tissues suggests low storage potential in eqb,

Question 10

what is stage one of nitrogen cycle

Answer 10

oxidation of ammonia to nitrite inside cells of Nitrosoccus bacteria

Question 11

what bacteria cause oxidation of ammonia

Answer 11

Nitrosoccus cause oxidation of ammonia to nitriteq

Question 12

what do Nitrosoccus bacteria do

Answer 12

oxidation of ammonia to nitrite

Question 13

what is stage 2 of nitrogen cycle

Answer 13

oxidation of nitrite to nitrate by Nitrobacter bacteria

Question 14

what does Nitrobacter do

Answer 14

oxidise nitrite to nitrate

Question 15

what bacterium oxidises nitrite to nitrate

Answer 15

nitrobacter

Question 16

what is the sole energy source of nitrobacter and nitrosoccus
what is it used for

Answer 16

oxidation is the sole energy source of these bacteria, used for chemosythetic assimilation of CO2

Question 17

what do nitrobacter and nitrosoccus do with the energy source from oxidation

Answer 17

they use it for chemosynthetic assimilation of CO2

Question 18

when/how does nitrate act as an oxidising agen

Answer 18

in the absence of oxygen, nitrate may act as an oxidising agent

Question 19

what condns needed for nitrate to act as oxidising agent

Answer 19

anaerobic

Question 20

how does nitrate act in anaerobic condns

Answer 20

as an oxidising agent

Question 21

how does nitrate act as an oxidising agen

Answer 21

gets reduced to nitrite by accepting a hydrogen acceptor

Question 22

what does nitrate get reduced to - how

Answer 22

nitrate gets reduced to nitrite by accepting a hydrogen

Question 23

under what condns does nitrate get reduced to nitrite

Answer 23

anaerobic condns

Question 24

what is it called when nitrate gets reduced to nitrite

Answer 24

denitrification

Question 25

name some nitrogen fixing bacteria

Answer 25

Azotobacter, Clostridium, Rhizobium

Question 26

what are Azotobacter, Clostridium and Rhizobium all examples of

Answer 26

nitrogen fixing bacteria

Question 27

name some nitrogen fixing blue green algae

Answer 27

Nostoc Anabena Cylindrospermum

Question 28

name some nitrogen fixing actinomycetes

Answer 28

Frankia on tree roots

Question 29

when does nitrogen fixation by nodulating bacteria stop

Answer 29

fixation by nodulating bacteria stops when fertiliser nitrogen is applied, because plants stop feeding the bacteria

Question 30

why does nitrogen fixation by nodulating bacteria stop when nitrogen fertiliser is applied to the plant

Answer 30

because plants stop feeding the bacteria carbohydrate, as it does not need the bacteria for nitrogen fixing

Question 31

at what soil pH does nitrogen fixation stop in plants

Answer 31

when pH falls below 4

Question 32

what form is nitrogen in in soil mostly?

Answer 32

97098% stable organic compounds half as protein N half as amino sugars,chitin,lignin

Question 33

how is soil nitrate lost quickly

Answer 33

by leaching

Question 34

what is leaching

Answer 34

loss of soil nitrate

Question 35

which form of ammonia has longer retention

Answer 35

ammonia (compared to nitrate)

Question 36

give an example of something with high carbon, low nitrogen ratio

Answer 36

wood

Question 37

what is the result of a high carbon low nitrogen ratio

Answer 37

slow decomposition low food quality long residence time in soil

Question 38

give an example of something with a high carbon nitrogen ratio

Answer 38

young leaves or meat

Question 39

what is the result of having a low carbon:nitrogen ratio

Answer 39

high food quality | rapid decomposition

Question 40

what does slow decomposition, low food quality and long residence time in soil suggest about the carbon:nitrogen ratio

Answer 40

high carbon low nitrogen eg.wood

Question 41

what does high food quality and rapid decomposition suggest about the carbon:nitrogen ratio

Answer 41

low c:n ratio

Question 42

what species are involved in nitrogen fixation in deserts

Answer 42

lichens of the desert crust

Question 43

what do lichens in the desert crust do

Answer 43

fix nitrogen

Question 44

how can nitrogen pollute the enviro

Answer 44

leaching into groundwater marine pollution from sewage and other terrestrial inputs movement of gaseous ammonia globally

Question 45

which ecosystems have the highest critical load of N

Answer 45

most terrestrial ecosystems

Question 46

which ecosystems are extremely sensitive and have a small critical load of N

Answer 46

soft water lakes and ombrotrophic mires

Question 47

how much of the nitrogen used in producing food do people eat?

Answer 47

only 10%

Question 48

what is the ratio of fertilizer input to N in product

Answer 48

3 wheat 14 dairy 21 meat

Question 49

which food product has the most fertilizer N put into it

Answer 49

21 meat (3 wheat 14 dairy)

Question 50

what are some atmospheric sources of nitrogen pollution

Answer 50

industry vehicle exhausts farm animals fertilizer dusts

Question 51

what is the park grass experiment

Answer 51

the longest running ecological experiment in the world - used to determine the optimal fertilizer regime for hay yield

Question 52

how and why are nitrogen and carbon cycles tightly coupled

Answer 52

coupled through processes of photosynthesis and decomposition because N is one of the resources that most commonly limits primary production

Question 53

what is the largest pool of N

Answer 53

atmospheric dinitrogen gas

Question 54

what shows that anthropogenic fluxes are now dominant components of the N cycle

Answer 54

the rate of fixation of atmospheric N2 by humans exceeds the rate of natural terrestrial biological fixation

Question 55

what are the main anthropogenic nitrogen fluxes

Answer 55

``` Haber-Bosch process growing crops -soybeans,alfafa and peas that have symbiotic relationships with nitrogen fixing bacteria fossil fuel combustion biomass burning deforestation volatilization of fertilisers emission from livestock feedlots human sewage treatment plants ```

Question 56

why is human growing of crops fixing more nitrogen into atmosphere

Answer 56

as they have symbiotic relationships with nitrogen0 fixing bacteria, increasing N2 fixation - oxygen taken but nitrogen released

Question 57

what experiment is used to determine the optimal fertilizer regime for hay yield

Answer 57

the park grass experiment

Question 58

for every ammonium ion taken up by plants, what is released into the soil

Answer 58

a hydrogen ion is released into the soil for every ammonium ion taken up by plants

Question 59

what effect on the soil does inputs in the form of sodiumnitrate have

Answer 59

non acidifying

Question 60

which fertilizer could you use that would be non acidifying

Answer 60

sodium nitrate

Question 61

which fertilizer could you use that would be strongly acidifying

Answer 61

ammonium sulphate

Question 62

what effect does adding ammonium sulphate as fertilizer have on soil

Answer 62

strongly acidifying

Question 63

what effect does nitrogen deposition have on biodiversity

Answer 63

it reduces biodiversity

Question 64

what effect have humans had on the rate of nitrogen input into the terrestrial nitrogen cycle

Answer 64

they have approx doubled it

Question 65

what effect have humans had on N2O concentrations

Answer 65

increased it - drive the formation of photochemical smog over large regions of Earth

Question 66

what causes the photochemical smog over large regions of Earth

Answer 66

increased conc of N2O and other nitrogen oxides

Question 67

after nitrogen, what is the next most importent macronutrient

Answer 67

phosphorus

Question 68

what is P required for

Answer 68

ADP/ATP production membranes nucleic acid

Question 69

in which ecosystems does phosphorus limit Primary production

Answer 69

terrestrial ecosystems with old, well weathered soils like tropical lowland forests and some freshwater

Question 70

what can phosphorus availability control the rate of

Answer 70

can control the rate of biological N2 fixation, due to its high metabolic demand for P

Question 71

in what way are the C, P and N cycles linked to eachother

Answer 71

through photosynth, NPP, deocmposition and N2 fixation

Question 72

what is Ps atmospheric pool

Answer 72

doesnt have one - dust

Question 73

where are the largest pools of P

Answer 73

in terrestrial soils and marine sediments

Question 74

how is P released from sedimentary rocks

Answer 74

by weathering

Question 75

what is labile P

Answer 75

P that is either in dissolved form or is readily released into solution

Question 76

what special techniques do plants have to get P

Answer 76

organic acid exudation mycorrhizae special root forms eg.proteoid roots

Question 77

what are proteoid roots

Answer 77

plants have these roots to enable them to get P

Question 78

why is P cycle more difficult to study compared to N cycle

Answer 78

it involves inorganic mineral reactions which tend to interfere with the availability of P in organic cycles + complicate measurement

Question 79

what does occluded mean

Answer 79

stuck into clay particle

Question 80

what bound forms of phosphorus exist

Answer 80

occluded and adsorbed P (adsorbed onto Fe and Al ions on clay surgace)

Question 81

describe soil age effects

Answer 81

more highly weathered soils tend to be high in Al and Fe therefore P tends to get "locked" up as occluded/adsorbed

Question 82

what nutrients do more highly weathered soils tend to be high in# what is the consequence of this

Answer 82

Al and Fe | P tends therefore to get locked up as it adsorbs onto Fe and Al ions on clay surfce

Question 83

how much % of total soil P is available in older soil

Answer 83

less than 1 % of total soil P is available in older soils

Question 84

which bound form of P is most tight

Answer 84

occluded P -probs gone for all time | adsorbed P is probs exchangable

Question 85

which bound form of P is probs to some extent exchangable

Answer 85

adorbed P

Question 86

what are TRFs limited in

Answer 86

P