seminar 2: Daniell Flashcards
what is the pessimistic and optimistic prediction by 2050 for the rise in human pop size?
10bn
plateau at 8bn
are the cereal production and human pop size lines parallel and what does this mean?
no
per person on the planet there is less food
- higher demand for increased yield
the Haber-Bosch process has been industrialised within the last century
- what is it?
- what % of the worlds energy is spent making ammonia from this process
- artificial N fixation process and the main industrial procedure for ammonia production today, splits 3 stable N bonds to form reactive N
- 2%
per unit of food production what is happening to use of N, particularly as fertiliser?
using more and more reactive N
what did steffen et al estimate and what were 3 things discovered?
safe operating space for a range of systems
- direct agricultural involvement
- N cycle beyond its limit so high risk
- P cycle beyond its limit and may run out
what does it mean we cant continue to do because the N cycle is beyond its limit?
cant put as much reactive N into atmosphere mainly from fertiliser as it causes eutrophication and GHG emission
according to 2016 UK estimates what % is due to agriculture and why is this an underestimate?
10%
does not include fertiliser production
in terms of GHG emissions from agriculture how does nitrous oxide compare to CO2?
- what is the main source for each of the gases?
N2O 3 times more potent than CO2
- CO2: fuel for agriculture
- methane: ruminants
- N20 from fertilised field and leakage from N cycle
when looking at the C footprint for malt production what % GHG emissions is from
- fuel
- N20 from soil
- N fertilsier
- 17%
- 35%
- 48%
from an EPA give 3 points on the nitric and adipic acid production industrial process for reducing emissions
- major source N20
- all processes involved have costs
- if all processes in play can save 79% GHG emissions
from an EPA give 4 points on the non rice croplands for reducing emissions
- no costs to reducing emissions such as if tillage of fields
- less fertiliser, less GHG emission
- sometimes increased fertiliser can reduce emissions
- if all processes in play can save only 10%
what does increasing N do to grain yield and why only until a point?
increases
saturation occurs
where is the EU on the yield response curve?
not adding N we need for optimum yield but are adding max fertiliser can for economic yield
- cost if reduce N
where is China on the yield response curve?
further along than EU as adding lots of fertilizer as is cheap but means poor N use efficiency and lots of GHG emissions and leaching damage
- gain if reduce N
where is Brazil on the yield response curve?
adding low levels of N
- if add more N can cut GHG emissions
in the N cycle is there competition?
yes for compounds in the system such as ammonia which is competed for by plants, microbes and nitrifiers
what are the stages of denitrification?
NO3 -> NO2 -> NO -> N20 -> N2
why is N fixation highly regulated?
very expensive so not fixed unless needed to such as in N limiting systems, for example legumes do this
what is soil made up of?
bacteria and aggregates surrounded by water film
small pores are often low in water, what will bacteria here do?
be denitrifying to maintain respiration using nitrogen oxides and nitrates as a different electron receptor to O2
in the soil and plant system why is there competition for nitrate?
plant uses it for assimilation
bacteria and fungi use it to maintain respiration
in the plant microbe interaction what does the plant do? (4)
- physically alters soil environment
- chemically alters by releasing nutrients and C
- releases signalling compounds that initiate plant microbe symbiosis
- produce antimicrobial compounds that interfere with quorum sensing and inhibit microbial activity
what are some issues that may arise from plant microbe interactions? (4)
- plant growth limited by nutrient availability and ammonia is used by microbes
- roots often outcompeted for N by microbes
- microbial transformations of N limit availability of N
- nitrifying bacteria convert ammonia to nitrate leading to loss of N
in a fertilised system what is there a flush of after it rains?
nitrous oxide
why was barley used as the plant model ?
small, diploid- can link results easily
what was the experimental procedure involving barley when looking at denitrification? (4)
- barley cultivars in pots
- gas measurement taken to see how much nitrous oxide released from soil
- screen to identify emission variation
- assessed soil condition effects
the plant is the C source in the system so what happens if no plant?
little respiration
what was nitrous oxide emission rate like in the barley cultivars?
varied between
in the follow up experiment:
- how many cultivars
- the watering treatments
- the sampling
- 4
- 70% water filled pore spaces (aerobic), 70,90,70 fluctuating, 90% anaerobic
- gas sample, plant parameters, microbial pop
in the follow up what was found?
- difference between cultivars as to when to stop exploring soil for nutrients
- little nitrous oxide emission at 90%
what was the exudate analysis set up? (6)
- separation of exudate effects
- no plant but same plotting system
- artificial exudate injected 0-3 mg C per pot daily for a week
- watered to 50%, 70%, 90%
- acetylene used to asses emission
- assessed community dynamics
what does acetylene do to emission when is used?
stabilises it
last denitrification step blocked so massive reduction in emission variation and more nitrous oxide emission
when a community is fed C what happens to it?
grows
what 2 genes encode nitrate reductase and what do they contain?
NirK (copper)
NirS (iron)
what forms with NirS?
anaerobic community
what are the 2 markers breaking down nitrous oxide?
clade i, clade ii
what was found when 4 cultivars of barley exudates were collected and analysed?
no effect when root exudate C was added to soil
what can root exudates moderate?
N cycling and drive soil activity
where is there significant variation?
N2O emission and nitrification
what are the effects?
indirect and on community structure
due to quantity and quality
why is soil condition critical?
if high N and low C - competition for C
same the other way round
what is the aim in the plants produced?
those that use more of the N and release less N as GHG
