L14

Question 1

N20 flux after fertilizer addition

Answer 1

• Peaks of N20 after fertilisation
  
  • Also after harvest and tillage
  • Peaks after NH4 not linked to nitrate accumulation
  • Higher stable water WFPS linked to lower emissions

Question 2

Respiration is high or low before fertiliser addition?

Answer 2

-High and then tails off

-Redistribution of carbon giving microbes access
- System flips from aerobic to anaerobic
-Not as much N20 release

Question 3

Denitrification

Answer 3

-Process takes electrons to reduce nitrogen oxides
- Maintaining respiration
- Largely distinct processes
- Keeping nitric oxide is toxic

Question 4

Modulation of activity and N fate

Answer 4

• pH (Last years lectures introduced this)

-O2 availability (affected by plant/soil respiration and WFPS)

-NO3 availability/concentration

-Available respirable carbon

Question 5

Spatial structuring of soil

Answer 5

• Soil is complex structurally
  
  • Range of aggregate sizes
  • Macroaggregates built from microaggregates
  • Conditions can vary over very short distances
  • Functional variability between colonies of same species
  • Community in system is likely derived from microaggregate community
  • Gradients across the pore spaces

Question 6

Rhizobox

Answer 6

• Key experiment equipment
  
  • Separate root growth from soil
  • Small processes eg micrometres but at larger scales is at constant risk of artefacts
  • Growing plant in thin sheet
  • Roots almost form a system boundary
  • Fine roots can’t grow through
    Gradients from root surface

Question 7

Rhizobox experiments- stable isotope labelling