GHG IMPORTANCE OF SOILS

Question 1

how much carbon do soils contain in Pg? how much additional carbon does permafrost contain?

Answer 1

1500-2400 PgC (Peta= 10^15)
permafrost contains an additional ~1700 PgC

Question 2

how much carbon do vegetation, oil reserves and atmosphere contain?

Answer 2

• 450-650 PgC
• 173-264 PgC
• ~730 PgC

Question 3

why are soils known as ‘nature’s recycling system’?

Answer 3

• they return biomass and nutrients to forms that can be used by the next “generation” of life

Question 4

how do soils support the growth of higher plants?

Answer 4

• they provide a medium for plant roots
• and supply nutrients that are essential for plant biomass and metabolism

Question 5

soils support the growth of … plants by providing a … for plant roots and supplying … that are essential for plant … and …

Answer 5

higher
medium
nutrients
biomass
metabolism

Question 6

soil properties are often in large part responsible for the types, … and biomass of … and microorganisms in ecosystems, and … the number of … (humans too) that vegetation can …

Answer 6

diversity
vegetation
indirectly
animals
support

Question 7

what services are provided by soil?

Answer 7

• microbes
• fungal hyphae/fungi
• nematodes
• mites
• springtails

Question 8

soils are home to phenomenal … and biodiversity

Answer 8

biomass

Question 9

what is humus? what is the A horizon?

Answer 9

carbon that has resisted degradation
- very slowly decomposed
- plant and microbial origin
- provides soil with its dark colour, especially in the A horizon
- A horizon is almost biologically active layer, with higher organic matter and nutrients

Question 10

which layer of soil is the most biologically active layer?

Answer 10

the A horizon

Question 11

what is cation exchange capacity critical for?

Answer 11

nutrient retention

Question 12

Colloids are the … particles: of … (mineral) or humus (organic), chemically …

Answer 12

smallest
clay
active

Question 13

Bioavailable … is often limiting for soil fertility

Answer 13

Phosphorus

Question 14

What factors can differ between soils?

Answer 14

• nutrient abundance and balance
• type of clay; proportion of various sized particles (sand, silt)
• pH (acidity, alkalinity)
• toxic elements
• salinity
• microbes

Question 15

what are the differences between upland soil and wetland soil?

Answer 15

upland soil= elevated, largely used for agriculture
wetland= low-lying, wet soil

Question 16

what are the uptakes and effluxes of forest soils?

Answer 16

CO2 uptake and storage through photosynthesis & prim production minus decomposition/respiration
CH4 uptake by methane-oxidising soil bacteria

CO2 efflux through autotrophic respiration (leaf, shoot and roots)
CO2 efflux through heterotrophic respiration (primarily from litter and SOM decomposition)
N2O efflux through microbial nitrification and denitrification processes

Question 17

large, old trees do not act simply as senescent … reservoirs, but actively … large amounts of carbon compared to … trees

Answer 17

carbon
fix
smaller

Question 18

what fraction of total global soil carbon do peatlands hold, despite only covering 3% of the Earth’s surface?

Answer 18

1/3

Question 19

how much % of all atmospheric CH4 do peatlands emit annually?

Answer 19

about 10%
- high water-table (when precipitation is ample) leads to anoxia, slow decomposition, but greater CH4 emissions

Question 20

why does Sphagnum peat decompose slowly?

Answer 20

• it is flooded, which makes it anoxic/anaerobic
• it is acidic
• it is nutrient poor

Question 21

explain physical degradation in terms of pasture.

Answer 21

compaction due to hoof traffic often associated with over-grazing

Question 22

bare soils are vulnerable to … and … erosion (physical degradation and erosion section)

Answer 22

wind
water

Question 23

what are the factors of chemical degradation?

Answer 23

• depletion of organic matter and nutrients (from vegetation loss)
• contamination with chemical pollutants
• salinization (in dry areas, esp with irrigation)
• desertification (only occurs in arid, semi-arid and dry sub-humid areas)

Question 24

what is salinisation?

Answer 24

• poor water management
• too much water evaporates from the surface
• salts left behind
• toxic to plants

Question 25

how does acid rain contribute to chemical degradation?

Answer 25

• causes flooding of cation exchange sites on soil colloids with protons
• displaces nutrients from cation exchange sites -> leached away -> no longer available for plant growth
• toxic aluminium is soluble in water at low pH (non-mobile and safe at neutral and high/basic pH) injures plants and soil microorganisms

Question 26

what are the major types of soil degradation?

Answer 26

• wind erosion
• chemical degradation
• physical degradation
• water erosion

Question 27

what are the underlying causes of soil degradation?

Answer 27

• deforestation
• industrial activity
• agricultural activity
• overgrazing
• overuse of vegetation (e.g. fuelwood)

Question 28

soil degradation is an additional threat to … security

Answer 28

food