theme d - agricultural sustainability Flashcards
what is global warming potential
- radiate efficiency - ability of gas to store energy/temperatures
- lifetime - how long they persist in the atmosphere
- comparison to co2 as standard
what is harber bosh
industrial process for producing ammonia fertiliser
- produced 450 million tonnes a year
historical and projected emissions from the agriculture sector
- general trend is increased emissions
- livestock and cropland section has increased
- rice sector has not changed beacuse mitigation strategies to reduce emissions have been implemented
how are livestock emissions predicted to change
- projected to increased by 10% by 2030
- mainly from farmed meat and milk
how are cropland emissions predicted to change
n2o - projected to account for 16% of total GHG emissions by 2030
- emissions have grown proportionally with the increased use of fertilisers
how are rice production emissions predicted by change
- account for 4% GHG emissions
- non OECD countries account for 84% of global rice cultivation emissions
what is the green revolution
- development of high yielding plan species
- more tilling and better application of fertiliser meant plants could growth more = higher food production
what is the periplasmic space
gram negative bacterial cell (between outer and inner membrane) wall where most of the processes in the nitrogen cycle take place
steps in the nitrogen cycle
- nitrogen fixation
- nitrification
- assimilation
- ammonification
- denitrification
ammonia oxidation in the nitrogen cycle
- first step
1. NH3 (ammonia) combines with oxygen and 2 hydrogen ions to form NH2OH and water (catalysed by AMO) (uses energy) - HAO then catalyses this further to No2- (nitrite) and 5H+ (produces energy used for next step)
nitrite oxidation in the nitrogen cycle
- second step
- NO2- combines with water to form NO3- and 2H+ and 2e (catalysed by NOX/NXR)
- this processes released energy
nitrification summary
- conversion of ammonia to nitrate
- aerobic processes
- example of a chemolithotroph process (energy is released and used to fix co2)
- very rapid process in fertilisation systems
why is nitrification an important process
- nitrate is more mobile in soils than ammonia which is positively charged (is bad as well as higher leaching risk)
- nitrate can be used as a substrate for denitrification
- releases N2O directly
history of studying nitrification
- recognised as a biological process in 1870s
- observed as a 2 stage process 1879
- in 1800s importance of Nitrobacter/ Nitrosomonas recognised
N turnover in fertilised soils
assessed the dynamics of inorganic N and nitrification rate after fertilisation
- was rapid loss of detectable ammonium
- loss of nitrate
- compost lower than inorganic additions
- synchronous nitrification rate
what is denitrification
- anaerobic process - does not occur when their is too much o2
- use N oxides instead
- conditions in the soil change when it rains as water stops o2 being present
spacial structuring of soil
what happens when it rains
condition in the soil change between aerobic and anaerobic when it rains as in saturated soils water sticks to aggregates by capillary action blocking o2
denitrifying enzymes
- nitrate reductase (not limited to denitrification)
- nitrite reductase - 2 mutually exclusive enzymes
- nitric oxide reductase (highly toxic and coordinately expressed with nitrite reductase and is used as a signalling molecule)
- nitrous oxide reductase (only biological sinks for N2O and has 2 clades)
what are the 2 different nitrite reductase enzymes
- one contains copper and encoded by NirK operon
- other contains iron (haem) and encoded by NirS operon
- used as a marker for a functional community
what is the problem with fertilisers
- N2O flux after addition
- harvest and tilling polluting
- leaching after rainfall
dominant N2O sources in wet and dry soils
- N2O emitted if denitrification is incomplete
- this happens because as a lack of nitrous oxide reductase activity (due to soil condition)
- wetter soils are more polluting as denitrification happened in them more
environmental conditions that affect N emissions
- O2 stability and levels
- pH
- nitrate and C levels
climate pledges to reduce methane emissions
COP26
- curb CH4 emissions by 30% by 2030
- signed by 103 countries
- $59 million in funds
COP28
- $1 billion grant in funding
- new commitments and legislation from top emitters
- new technology employed (alert and response systems)
- signed by 155 countries
how much does agriculture account for methane emissions
42%
cellulose as food
- difficult to digest - no mammal has the ability
- herbivores have to break it down as there main source of energy
- heavy reliance on microbial consortia to break sown the polymer and utilise the breakdown products
- ruminants have the most efficient strategy
the rumen
- grass it eaten quickly by cursory chewing mixing with lots of saliva
- its swallowed into the rumen and churned constantly
- fermentation processes starts: temp 28-42, pH 7, anaerobic)
the reticulum
large or buoyant pieces that floated in become concentrated or forms into ball (due to honeycomb structure) and regurgitates and rechewed
the omasum
when food is fully broken down it is passed here where muscular action continues to break it down
the abomasum
digestive enzymes are secretes and start to digest the remains of the food and microbes (form part of the bolus)
the caecum
last location where the food is broken down and anything remaining will be excretes
ruminants digestive system
- rumen
- reticulum
- omasum
- abomasum
- caecum
process of glycolysis
- first step in respiration
- net gain of 2 ATP and 1 NADH
Krebs cycle
- net gain 2ATP, 8NADH, 2FADH2
how are complex biopolymers broken down
- hydrolysis - broken down into monomers and oligomers (sugars, aa peptides)
- acidogenesis - fermentative bacteria break it down into propionate butyrate (short chain volatile organic acids)
- acetogenesis - fermentative bacteria break this down into H2 +co2 or acetate (h2 producing)
- methanogenesis - co2 reducing methanogens or acetolactic methanogens break it down in to CH4 + co2
how is methane produced in a paddy field
- happened because it is flooded creating very anaerobic soils
- for a plant to survive it creates channels that methane can enter at the root which is subsequently released through the stomata
- as methane passes through the aerobic top layer of the soil it is utilised by bacteria then released
types of large scale models for emissions
- tier 1 - simple models based on baseline emission factors and scaling factors
- tier 2 - uses country/region specific data
- tier 3 - combines factors with key things such as, pH, cropping and water practices
biogas plants
- can produce biomethane, electrical energy and thermal energy and natural fertilisers
- however takes land away from food consumption as farmers start producing food to use for biogas instead as it is more profitable - problem as humans need food
mitigation of emissions from livestock production - enteric fermentation methods
- aim to reduce methane emissions
- direct - antimutagens, propionate precursors
- indirect - growth hormones (plants grow faster so are harvested earlier so have less time to produce ch4 if not already operating on plateau)
- feed related - intensive grazing, precursors
- ethical and contamination concerns - hormones treatment, antibiotics
mitigation of emissions from livestock production - manure management methods
- aim to reduce methane and nitrogen oxide emissions
- n2o interruption of cycling - saving methane use
- digestion using methanogenesis
- engine conversion of methane
- expensive to install so only found in developed countries
why are novel methodologies required to combat high agricultural emissions
- because there is a lack of opportunity to reduce emissions
- trade emissions?
- fund research into novel solutions
- reduce waste in the food system to reduce demand - over 30% is currently lost as waste
- need to focus on small marginal gain that cumulatively will cause a large reduction in emissions
how will altering fertilisation of agricultural land change emissions
- decrease in n2o emissions and ammonia
- large decrease in leaching and runoff
- increased yield as N stays in the system for longer
- more profitable in the long run despite being more labour intensive
biological nitrification inhabitation
- plant root exudates can inhibit ammonium oxidation of chemical inhibitors
- inducible
- variation across crop cultures
- opportunity for application as a breeding target
mycorrhizal systems
- highly mycorrhizal systems emit less n2o by skewing denitrification communities - this increased biomass and alters the fate of plant C
- agronomical practice has deleterious effects of AMF populations
- increase levels of AMF colonisation in agriculture
use of biochar
- can be used as an agronomic additive
- has many impacts
- has potential to reduce n2o emissions
- mechanisms for this is very obscure
manipulation of rumen microbiome
to reduce ghg emissions
- improves efficiency and reduces methane
- feed supplements
- constitutions of forage
- they alter the microbiomes to disfavour methanogens
examples of novel methodologies to reduce emissions
- manipulation of rumen microbiome
- altering fertilization
- biological nitrification inhibition
- mycorrhizal systems
- use of biochar
phosphorus chemistry and facts
- Highly reactive
- Found in either an inorganic or organic form
- Most simple and bioavailable form is liable P which is orthophosphate
- However liable P is very reactive
- In terrestrial and marine ecosystems, phosphate forms inorganic and organic complexes – requires conversion back to liable P before it can be taken up by organisms
- EU has banned use of glyphosate since 2020 but not Britain (helped win over Brexit votes by farmers)
how is phosphorus essentilal for cullular functioning
-DNA/RNA
-Phospholipids
-ATP
-Cell signalling and gene regulation
the three major pools of P
- liable P
- organic P
- inorganic P
about liable P
- found in soils
- insoluble
about organic p
- Plants cannot take up this form, so it is converted into labile form
- Phosphate undergoes esterification with carboxylic acids
- COP bond
- Phosphomonoesters, phosphodiesters, phosphotriesters and phosphonates
what are phosphotriesters
- marine bacteria capable of degrading anthropgenic pollutants
- possible newly evolved
- ecosystem pertubation
what are phosphonates
- have a CP bond
- fucntional role is still crypric
- found in outer membrane of polysaccharides and can replace lipids
- abundant in global ocean and plant tissue
- play a major role in the marine P cycle - redox cycle and phytoplanton involved
global P cycling in the enrvionement
- ocean floor contains the largest reserve of P - Microbes in marine sediments = organic P – phosphate - Released into water column
- Ocean currents circulate liable P to surface - Photic zone – fuels phytoplankton growth = co2 fixation and export to deep ocean - balance between available light and nutrient availability drives seasonal phytoplankton growth
- Deep ocean is a biological C pump
how does phosphorus availability impact global processes
-Limits global primary production – land and sea
-Direct and indirect (limitation of nitrogen fixation by microbes) impact global C cycling
-Important consequences for:
1. The removal of atmospheric co2 – soil and deep-sea export
2. Food production – plants and animals
biological controls on P availability
-Labile P locked up in inorganic and organic stores
-Organisms can release liable P from these complexes by 2 methods:
1. Solubilisation - Driven by chemical processes and manipulate by metabolism -more important in soil than seawater
2. Mineralisation -Enzymatic process - Lots of microbial enzymes can degrade organic P
how do phosphates drive remineralisation
-in response to low P availability, microbes produce enzymes called phosphatases
-Huge diversity of them
-Promiscuous (wide) and specific substrate range
-Have different cellular localisation
example of PafA driving remineralisation
- Predominantly found in a certain group of bacteria – phylum Bacteroidetes
- Efficiently remineralised organic P into bioavailable inorganic phosphate
- Exiting enzyme for improving sustainable agriculture
impacts on sustainability - agriculture
- Loss of habitat and wildlife
- intensive farming relies on the application of chemical P fertilisers (made of phosphate minerals from the apatite group)
- Results in major global imbalances
- Caused eutrophication in marine environments when washed away by surface runoff – economic damage to coastal communities
- Depletion of natural resources (rock phosphate is a expensive finite resource that id found in few geographic locations)
- Food security
how does P affect the global C cycle
- Impact on co2 drawdown
- Plant production increased with elevated co2 (fertilisation effect) - Impact of soil respiration – co2 release
- In soil liable and recalcitrant C stocks
- Vulnerable to increased degradation under global change
