EE23

Question 1

What is often the most limiting nutrient for plant growth?

Answer 1

nitrogen

• essential for manu defensice chemicals and animal physiology
  eg. Alkaloid have important physiological effects eg. morphine, nicotine

Question 2

NH4+
NO3-
NO2-
N2O
NO

Answer 2

ammoninum ion
nitrate ion
nitrite ion
nitrous oxide
nitric oxide

Question 3

What causes the fundemental fluxes in nitrogen?

Answer 3

biomass 
N-uptake by roots
N-excretion 
Nitrification
Denitrification

Question 4

which organisms can initiate nitrogen fixation

Answer 4

bactera like Azotobacter and clostridium
nodulating bacterial rhizobium
blue green algae nostoc anabeana and cylindrospermium
actinomysetes like frankia on tree roots

Question 5

Describe nitrification

Answer 5

nitric acid formed in soil as result of bacterial oxidation in soil
1. nitrosoccus bacteria
ammonia -> nitrite
2. nitrobacter
nitrite - nitrate

Question 6

What are the nitrogen sinks?

Answer 6

atmosphere as molecular N2
denitrification in wetlands and aquatic 
storage in forest biomass
sediments
*high turnover in living tissues = low storage potential in equilibrium

Question 7

Describe denitrification

Answer 7

in the absence of o2 nitrate acts as a H acceptor
oxidising agent
reduced to nitrite
some bacteria do this
other bacteria oxidise ammonium to free N2 at low pH in water logged soils.

Question 8

What is the composition of nitrogen in the soil?

Answer 8

0.1 -0.3% of dry mass
-2.3% soil n= nitrate/ammonia
-97/98% in stable organic compounds
-50% protein
50% aminosugars, chitin, aminosugars, lignin
- soil nitrate = quickly lost by leaching
- ammonia = longer retention

Question 9

What is the relationship between rhizobium and legumes?

Answer 9

plant pays carbohydrates for fixed nitrogen
fixation by modulating bacteria stops when fertilizers N applied. plant stop feeding bacteria
fixation stops when soil pH falls below 4

Question 10

Give an example of a high carbon: low N ratio?

Answer 10

eg. wood. slow decompostion
= low food quality
= long residence time in soil

Question 11

Give an example of a low carbon: high N ratio

Answer 11

eg. young leavers, meat
=high food quaility
rapid decomposition

Question 12

What does nitrogen flux in deserts involve?

Answer 12

lichens of desert crust
NO3- ——denitrification——–> N2—- fixation—–> cyanobacteria—–death/ammoniafixation—->NH4——nitrification—–>N03-

Question 13

Describe nitrogen pollution

Answer 13

atmospheric depotion =2-6 kg/ha/yr in 1970
today = 15-60 kg/ha/yr
- leaching nitrates - ground water
- marine pollution- sewage and terrestrial input

Question 14

What are critical loads?

Answer 14

Critical loads and levels are a tool for assessing the risk of air pollution impacts to ecosystems.

Question 15

What are the critical loads of mires and most terrestrial ecosytems of nitrogen?

Answer 15

15-20kg/ha/yr in miewa
most terrestrial ecosystems
= 15-20kg/ha/yr
* many parts of the industrial world have inputs much higher than these sometimes over 100kg/ha/yr

Question 16

What are sources of atmospheric nitrogen pollution?

Answer 16

industry
vehical exhaust 
farm aninmals
fertiliser dust
people only eat 10% of nitrigen used in food prod
3:14:21 wheat:fairy:meat n ratios

Question 17

What affect does nitrogen deposition have on biodiversity?

Answer 17

reduces it

Question 18

what relationship does species richness have with biomass and soil pH?

Answer 18

biomass - species richess decreases with biomass

soil ph - species richness increases with soil ph

Question 19

What are fertilizer inputs in the form of?

Answer 19

sodium nitrate - non acidifying

ammonium sulphate is strongly acidifying - for every Nh3+ ion taken up by plants, a H+ is released into the soil

Question 20

After nitrogen what is the next most important macronutrient?

Answer 20

phosphorous
required for ADP and ATP membranes and nucleic
acids
- p cycling includes significant inorganic mineral interactions which make it harder to study

Question 21

What are some phosphorous pools?

Answer 21

organic mattter
soluble P in dissolved form or readily released in sln
P in minerals and occluded P
* techniques to get P = organic acid exudation, mycorrhizia, proteozic roots

Question 22

What is the composition in more highly weathered soils?

Answer 22

higher in Al and Fe
-phos locked up
>1% total p available

Question 23

What is absorbed P?

What is occluded P?

Answer 23

absorbed P = +Al/Fe on clay surface - kinda exchangable

occluded P = stuck in clay aprticle - gone forever

Question 24

What are tropical forests limited by?

Answer 24

P

Question 25

What affect has human activity had on nitrogen pools?

Answer 25

• approx doubled rate of nitrgoen input in terrestrial nitrogen cycle
  -rates still increasing
• increased global conc greenhouse gas N2O and other N oxidises = drive formation of photochemical smog
• causes loss of soil nutrients Ca, K essential to long erm soil fertility
• contributed to acidification of soil, streams, lakes
  -increased transfer of N through rivers, esturies and oceans
• accelerated loss of biodiversity
  especially by plants adapted to efficient N use