Lecture 6: the matter of life & death

Question 1

Most of the carbon fixed by plants passes into ____

Answer 1

soil

Question 2

soil contains __ times the amount of carbon in vegetation and __ times the amount in atmosphere

Answer 2

3 times in vegetation

2 times in atmosphere

Question 3

biofuel carbon debt =

Answer 3

the effect of land use change on vegetation and soil C stores
- hard to repay

Question 4

decomposition and release of plant-available nutrients from organic molecules requires: (soil properties)

Answer 4

1) moisture
2) oxygen
3 )moderate pH
4) moderate temperature
5) active microbial populations
6) decomposable organic matter

Question 5

peatlands and carbon storage

Answer 5

< 3% of the earths land surface but contain > than one third of the global soil C and soil N

Question 6

Sphagnum moss and C storage

Answer 6

is rich in Phenolic acids, has high C:N ratios and traps water forming anaerobic _________

Question 7

In the UK where high soil C is associated with

Answer 7

-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)

Question 8

soil types vary by

Answer 8

typography??

Question 9

over-grazing of the UK uplands, soil compaction and vegetation removal leads to

Answer 9

increased soil loss

Question 10

there are over ____tonnes of C in the UK soils, total UK emissions in 2008 = _____tonnes

Answer 10

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

Question 11

plant litter: (going back into soil)

Answer 11

C: cellulose, lignin
N: proteins, nucleic acids
P: nucleic acids, phospholipids

Question 12

microbial litter 
(going back into soil)

Answer 12

C: polysaccharides, chitin, melanin
N: proteins, nucleic acids,
P: nucleic acids, phospholipids, techoic acids

Question 13

litter controls on decomposition rates: calluna stems

Answer 13

low decay rate so carbon accumulates in soil (graph)

Question 14

root or shoot litter decays slower

Answer 14

root

• can be protected by substances such as clays
• more lignin

Question 15

in cold climate high altitude and high latitude environments decomposition and nutrient cycling is (high montane, tundra)

Answer 15

slow (so lots of carbon but hard to grow things here)

Question 16

organic carbon is depleted under most ____ land and _______

Answer 16

arable land and rotational grasslands (less C)

Question 17

East Anglian Fenlands (Fens) carbon emissions

Answer 17

• 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

Question 18

litter high C:N ratios on decay =

Answer 18

low decay rates

Question 19

litter which is most acidic decays the

Answer 19

slowest

Question 20

C:N determines whether

Answer 20

plant needs to obtain nutrients from soil (immobilisation) to decay
-high C:N slow decay

Question 21

shoot & root litter chemistry the same?

Answer 21

no

-hence y roots take longer to decay

Question 22

condensed tannin??

Answer 22

protein is complexed with organic compound smokes it difficult to decay

Question 23

spruce trees and tannins

Answer 23

have tannins so decay is slower

Question 24

tannins ultimately

Answer 24

protect organic matter from decay

Question 25

increasing removal of Maize stalks results in

Answer 25

less carbon in soil

-farmers => payed to sell straw, no ones paying you to put it back in –> long term problems

Question 26

burning forests and carbon storage –> quick fix?

Answer 26

• charcoal
• carbons stays in soil for much longer of time
• bio-char has very low decay rate

Question 27

negatives + positives to bio-char

Answer 27

N

• not all benefits to organic carbon
• not a food source for microbes

P

• stability
• potential way to increase C storage in soil

Question 28

global carbon budget = 1870-2016

Answer 28

coal, oil, gas, cement increase atmosphere CO2

land and ocean sink reduced but not enough at all

Question 29

land use and land management effects on soil organic carbon

Answer 29

• land use change
• crop rotations (leys)
• tillage methods
• inputs

Question 30

more carbon in soil on yields

Answer 30

= better yields!!

Question 31

over 70% of UK arable soils have less than _% organic matter

Answer 31

4%

-less than whats required for agriculture

Question 32

increased earthworm population:

Answer 32

• increases soil aggregate stability in water
• increases soil organic matter
• increases soil water-holding capacity
• FEEDBACK POSITIVE

Question 33

sweden lets and carbon evidence

Answer 33

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

Question 34

graze pasture / arable soils have more carbon in soil

Answer 34

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)