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HELENP EE Ecology > EE Lecture 23: Nitrogen > Flashcards

EE Lecture 23: Nitrogen Flashcards

1
Q

what is often the most limiting nutrient for plant growth

A

nitrogen -aas,proteins,enzymes

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2
Q

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

A

alkaloids

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3
Q

what is formula for nitrateq

A

NO3-

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4
Q

what is formula for nitrite

A

NO2- (has 2 i’s therefore 2 Os)

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5
Q

what is formula for nitrous oxide

A

N20

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6
Q

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

A

atm
soils and orgs
4 orders of magnitude difference

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7
Q

outline some fluxes of Nitrogen

A 
biomass
N uptake by roots
N excretion
Nitrification
Denitrification
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8
Q

how/when is nitrogen lost

A 
with years of cultivation
at increased temperatures
by conversion to nitrate followed by leaching
fire - biomass combustion
lost to sediments as well
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9
Q

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

A

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

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10
Q

what is stage one of nitrogen cycle

A

oxidation of ammonia to nitrite inside cells of Nitrosoccus bacteria

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11
Q

what bacteria cause oxidation of ammonia

A

Nitrosoccus cause oxidation of ammonia to nitriteq

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12
Q

what do Nitrosoccus bacteria do

A

oxidation of ammonia to nitrite

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13
Q

what is stage 2 of nitrogen cycle

A

oxidation of nitrite to nitrate by Nitrobacter bacteria

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14
Q

what does Nitrobacter do

A

oxidise nitrite to nitrate

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15
Q

what bacterium oxidises nitrite to nitrate

A

nitrobacter

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16
Q

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

A

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

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17
Q

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

A

they use it for chemosynthetic assimilation of CO2

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18
Q

when/how does nitrate act as an oxidising agen

A

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

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19
Q

what condns needed for nitrate to act as oxidising agent

A

anaerobic

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20
Q

how does nitrate act in anaerobic condns

A

as an oxidising agent

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21
Q

how does nitrate act as an oxidising agen

A

gets reduced to nitrite by accepting a hydrogen acceptor

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22
Q

what does nitrate get reduced to - how

A

nitrate gets reduced to nitrite by accepting a hydrogen

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23
Q

under what condns does nitrate get reduced to nitrite

A

anaerobic condns

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24
Q

what is it called when nitrate gets reduced to nitrite

A

denitrification

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25
Q

name some nitrogen fixing bacteria

A

Azotobacter, Clostridium, Rhizobium

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26
Q

what are Azotobacter, Clostridium and Rhizobium all examples of

A

nitrogen fixing bacteria

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27
Q

name some nitrogen fixing blue green algae

A

Nostoc
Anabena
Cylindrospermum

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28
Q

name some nitrogen fixing actinomycetes

A

Frankia on tree roots

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29
Q

when does nitrogen fixation by nodulating bacteria stop

A

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

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30
Q

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

A

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

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31
Q

at what soil pH does nitrogen fixation stop in plants

A

when pH falls below 4

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32
Q

what form is nitrogen in in soil mostly?

A

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

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33
Q

how is soil nitrate lost quickly

A

by leaching

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34
Q

what is leaching

A

loss of soil nitrate

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35
Q

which form of ammonia has longer retention

A

ammonia (compared to nitrate)

36
Q

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

A

wood

37
Q

what is the result of a high carbon low nitrogen ratio

A

slow decomposition
low food quality
long residence time in soil

38
Q

give an example of something with a high carbon nitrogen ratio

A

young leaves or meat

39
Q

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

A

high food quality

rapid decomposition

40
Q

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

A

high carbon low nitrogen eg.wood

41
Q

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

A

low c:n ratio

42
Q

what species are involved in nitrogen fixation in deserts

A

lichens of the desert crust

43
Q

what do lichens in the desert crust do

A

fix nitrogen

44
Q

how can nitrogen pollute the enviro

A

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

45
Q

which ecosystems have the highest critical load of N

A

most terrestrial ecosystems

46
Q

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

A

soft water lakes and ombrotrophic mires

47
Q

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

A

only 10%

48
Q

what is the ratio of fertilizer input to N in product

A

3 wheat 14 dairy 21 meat

49
Q

which food product has the most fertilizer N put into it

A

21 meat (3 wheat 14 dairy)

50
Q

what are some atmospheric sources of nitrogen pollution

A

industry
vehicle exhausts
farm animals
fertilizer dusts

51
Q

what is the park grass experiment

A

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

52
Q

how and why are nitrogen and carbon cycles tightly coupled

A

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

53
Q

what is the largest pool of N

A

atmospheric dinitrogen gas

54
Q

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

A

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

55
Q

what are the main anthropogenic nitrogen fluxes

A 
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
56
Q

why is human growing of crops fixing more nitrogen into atmosphere

A

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

57
Q

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

A

the park grass experiment

58
Q

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

A

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

59
Q

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

A

non acidifying

60
Q

which fertilizer could you use that would be non acidifying

A

sodium nitrate

61
Q

which fertilizer could you use that would be strongly acidifying

A

ammonium sulphate

62
Q

what effect does adding ammonium sulphate as fertilizer have on soil

A

strongly acidifying

63
Q

what effect does nitrogen deposition have on biodiversity

A

it reduces biodiversity

64
Q

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

A

they have approx doubled it

65
Q

what effect have humans had on N2O concentrations

A

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

66
Q

what causes the photochemical smog over large regions of Earth

A

increased conc of N2O and other nitrogen oxides

67
Q

after nitrogen, what is the next most importent macronutrient

A

phosphorus

68
Q

what is P required for

A

ADP/ATP production
membranes
nucleic acid

69
Q

in which ecosystems does phosphorus limit Primary production

A

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

70
Q

what can phosphorus availability control the rate of

A

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

71
Q

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

A

through photosynth, NPP, deocmposition and N2 fixation

72
Q

what is Ps atmospheric pool

A

doesnt have one - dust

73
Q

where are the largest pools of P

A

in terrestrial soils and marine sediments

74
Q

how is P released from sedimentary rocks

A

by weathering

75
Q

what is labile P

A

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

76
Q

what special techniques do plants have to get P

A

organic acid exudation
mycorrhizae
special root forms eg.proteoid roots

77
Q

what are proteoid roots

A

plants have these roots to enable them to get P

78
Q

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

A

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

79
Q

what does occluded mean

A

stuck into clay particle

80
Q

what bound forms of phosphorus exist

A

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

81
Q

describe soil age effects

A

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

82
Q

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

A

Al and Fe

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

83
Q

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

A

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

84
Q

which bound form of P is most tight

A

occluded P -probs gone for all time

adsorbed P is probs exchangable

85
Q

which bound form of P is probs to some extent exchangable

A

adorbed P

86
Q

what are TRFs limited in

A

P

HELENP EE Ecology (8 decks)

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