Grassland Soil Sequestration

Question 1

60% belowground NPP due to…

Answer 1

SOC chemical composition: aliphatic compounds and root exudates

Question 2

Root input stabilization…

Answer 2

5x more SOC stabilization than aboveground inputs

Question 3

What are the types of SOC?

Answer 3

Particulate Organic Matter or Mineral-Associated Organic Matter

Question 4

Particulate Organic Matter

Answer 4

Formed by plant/microbial residue fragmentation, being large polymers

Question 5

Minera-Associated Organic Matter

Answer 5

Single small molecules leached from plants/exuded by roots, associating to minerals

Question 6

MAOM properties relative to POM…

Answer 6

Lower C:N ratio, longer residsence time, strongly bonding to minerals and physical protection in fine aggregates contributing to longer carbon sequestration.

Question 7

MAOM transforming rates for root exudates, root tissues, and aboveground carbon residues.

Answer 7

46%, 9%, and 7%

Question 8

Crop POM transformation…

Answer 8

19%, root-based plants thus contributing more to C sequestration

Question 9

MAOM in grassland top-soils…

Answer 9

50-75% of SOC MAOM with lower C:N ratio, with MAOM requiring more nitrogen for equivalent SOC accrucal than SOC

Question 10

POM/MAOM formation

Answer 10

POM by climate, whilst MAOM by soil properties (silt/clay content, cec, and microbial nitrogen availability)

Question 11

MAOM Saturation

Answer 11

Topsoil C storage at 50 g C kg soil with 80% European grasslands below saturation

Question 12

SOC stability…

Answer 12

85% stable, not impacted unless disturbed, 15% active carbon impacted by management

Question 13

Key driver of SOC formation/storage…

Answer 13

Plant diversity with elevated SOC inputs…

Question 14

Microbial contribution to total SOC…

Answer 14

Ranges from 23-74%, 50% on average

Question 15

When is microbial necromass carbon maximised?

Answer 15

900-1000mm mean annual precipitation

Question 16

Biggest drivers of rangeland carbon stocks…

Answer 16

Soil quality and weather over grazing itself

Question 17

A meta-analysis of grazing…

Answer 17

83 studies on extensive grazing across 164 sites show SOC storage decreasing with grazing, but is variable with climate (moist cool decreasing by 19%)

Question 18

Example of grassland sequestration variation..

Answer 18

Grazing management throughout the year: one year -5.40 t CO2 ha/yr, with the next 6.17 CO2 ha/yr

Question 19

Grassland climate distribution…

Answer 19

67% in semiarid, arid, and cold climates, with only 24% in humid climates, making C sequestration sensitive to CC

Question 20

Grasslands in semiarid climates…

Answer 20

Warming enhances C input but inhibits MAOM decomposition by fungal growth suppression, increasing MAOM pool.

Question 21

Grasslands in humid climates…

Answer 21

Negligible C sequestration, C4 grass cover and C4 derived carbon input increases, but decay rate increases also.

Question 22

Carbon sensitive to warming…

Answer 22

Topsoil recalcitrant carbon pool reduces to 14% as warming increases ligninase to cellulase activity

Question 23

POM/MAOM climate sensitivity…

Answer 23

POM 3x more change than MAOM

Question 24

Natural grassland grazing…

Answer 24

Wild ungulates enhance SOC storage due to short grazing periods, maintaining plant cover, diversity, productivity, and promotion of species with depp roots

Question 25

What does MAOM formation increase with?

Answer 25

Increased plant labile carbon inputs with increased root inputs

Question 26

Bioturbators impact on soils.

Answer 26

Loosen soils exposing larger aggregates of SOM to organo-mineral interaction by vertical soil mixing

Question 27

Improve grasslands sequestration rates…

Answer 27

Increase SOC stocks by 0.47 Mg C ha/yr