Lecture 6: the matter of life & death Flashcards
Most of the carbon fixed by plants passes into ____
soil
soil contains __ times the amount of carbon in vegetation and __ times the amount in atmosphere
3 times in vegetation
2 times in atmosphere
biofuel carbon debt =
the effect of land use change on vegetation and soil C stores
- hard to repay
decomposition and release of plant-available nutrients from organic molecules requires: (soil properties)
1) moisture
2) oxygen
3 )moderate pH
4) moderate temperature
5) active microbial populations
6) decomposable organic matter
peatlands and carbon storage
< 3% of the earths land surface but contain > than one third of the global soil C and soil N
Sphagnum moss and C storage
is rich in Phenolic acids, has high C:N ratios and traps water forming anaerobic _________
In the UK where high soil C is associated with
-upland areas with high rainfall and low temps
-often v acid conditions
-water logging common
-microbial populations have low activity
-litter v chemically resistant to decay
(and some lowland peats - the Fens)
soil types vary by
typography??
over-grazing of the UK uplands, soil compaction and vegetation removal leads to
increased soil loss
there are over ____tonnes of C in the UK soils, total UK emissions in 2008 = _____tonnes
there are over 10 000 000 000 (10 thousand million) tonnes of C in the UK soils, total UK emissions in 2008 = 170 000 000 tonnes
plant litter: (going back into soil)
C: cellulose, lignin
N: proteins, nucleic acids
P: nucleic acids, phospholipids
microbial litter (going back into soil)
C: polysaccharides, chitin, melanin
N: proteins, nucleic acids,
P: nucleic acids, phospholipids, techoic acids
litter controls on decomposition rates: calluna stems
low decay rate so carbon accumulates in soil (graph)
root or shoot litter decays slower
root
- can be protected by substances such as clays
- more lignin
in cold climate high altitude and high latitude environments decomposition and nutrient cycling is (high montane, tundra)
slow (so lots of carbon but hard to grow things here)
organic carbon is depleted under most ____ land and _______
arable land and rotational grasslands (less C)
East Anglian Fenlands (Fens) carbon emissions
- 88% of area is cultivated for agriculture
- nearly 40% of vegetables produced in england come fro there
- but peat wastage by oxidation, compaction and shrinking causes loss of 2.1cm/year
- lesss than 50-100 years of cropping left
- losing a lot of Carbon
litter high C:N ratios on decay =
low decay rates
litter which is most acidic decays the
slowest
C:N determines whether
plant needs to obtain nutrients from soil (immobilisation) to decay
-high C:N slow decay
shoot & root litter chemistry the same?
no
-hence y roots take longer to decay
condensed tannin??
protein is complexed with organic compound smokes it difficult to decay
spruce trees and tannins
have tannins so decay is slower
tannins ultimately
protect organic matter from decay
increasing removal of Maize stalks results in
less carbon in soil
-farmers => payed to sell straw, no ones paying you to put it back in –> long term problems
burning forests and carbon storage –> quick fix?
- charcoal
- carbons stays in soil for much longer of time
- bio-char has very low decay rate
negatives + positives to bio-char
N
- not all benefits to organic carbon
- not a food source for microbes
P
- stability
- potential way to increase C storage in soil
global carbon budget = 1870-2016
coal, oil, gas, cement increase atmosphere CO2
land and ocean sink reduced but not enough at all
land use and land management effects on soil organic carbon
- land use change
- crop rotations (leys)
- tillage methods
- inputs
more carbon in soil on yields
= better yields!!
over 70% of UK arable soils have less than _% organic matter
4%
-less than whats required for agriculture
increased earthworm population:
- increases soil aggregate stability in water
- increases soil organic matter
- increases soil water-holding capacity
- FEEDBACK POSITIVE
sweden lets and carbon evidence
statistical evidence that a higher proportion of leys in crop rotations = increased carbon in soils
BUT there is some papers that contradict this?? but this evidence is weak
graze pasture / arable soils have more carbon in soil
graze pasture
-because inputs into system (manure - carbon stable by digestion process, nitrogen fertiliser - carbon fixed by crop = more in soil, mow it back into land)
