EE23 Flashcards
What is often the most limiting nutrient for plant growth?
nitrogen
- essential for manu defensice chemicals and animal physiology
eg. Alkaloid have important physiological effects eg. morphine, nicotine
NH4+ NO3- NO2- N2O NO
ammoninum ion nitrate ion nitrite ion nitrous oxide nitric oxide
What causes the fundemental fluxes in nitrogen?
biomass N-uptake by roots N-excretion Nitrification Denitrification
which organisms can initiate nitrogen fixation
bactera like Azotobacter and clostridium
nodulating bacterial rhizobium
blue green algae nostoc anabeana and cylindrospermium
actinomysetes like frankia on tree roots
Describe nitrification
nitric acid formed in soil as result of bacterial oxidation in soil 1. nitrosoccus bacteria ammonia -> nitrite 2. nitrobacter nitrite - nitrate
What are the nitrogen sinks?
atmosphere as molecular N2 denitrification in wetlands and aquatic storage in forest biomass sediments *high turnover in living tissues = low storage potential in equilibrium
Describe denitrification
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.
What is the composition of nitrogen in the soil?
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
What is the relationship between rhizobium and legumes?
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
Give an example of a high carbon: low N ratio?
eg. wood. slow decompostion
= low food quality
= long residence time in soil
Give an example of a low carbon: high N ratio
eg. young leavers, meat
=high food quaility
rapid decomposition
What does nitrogen flux in deserts involve?
lichens of desert crust
NO3- ——denitrification——–> N2—- fixation—–> cyanobacteria—–death/ammoniafixation—->NH4——nitrification—–>N03-
Describe nitrogen pollution
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
What are critical loads?
Critical loads and levels are a tool for assessing the risk of air pollution impacts to ecosystems.
What are the critical loads of mires and most terrestrial ecosytems of nitrogen?
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
What are sources of atmospheric nitrogen pollution?
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
What affect does nitrogen deposition have on biodiversity?
reduces it
what relationship does species richness have with biomass and soil pH?
biomass - species richess decreases with biomass
soil ph - species richness increases with soil ph
What are fertilizer inputs in the form of?
sodium nitrate - non acidifying
ammonium sulphate is strongly acidifying - for every Nh3+ ion taken up by plants, a H+ is released into the soil
After nitrogen what is the next most important macronutrient?
phosphorous
required for ADP and ATP membranes and nucleic
acids
- p cycling includes significant inorganic mineral interactions which make it harder to study
What are some phosphorous pools?
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
What is the composition in more highly weathered soils?
higher in Al and Fe
-phos locked up
>1% total p available
What is absorbed P?
What is occluded P?
absorbed P = +Al/Fe on clay surface - kinda exchangable
occluded P = stuck in clay aprticle - gone forever
What are tropical forests limited by?
P
