Power Point Presentation for CAES Research Symposium 2012

1. Carbon Flux in Relation to Redox
Oscillations of Iron (II) in Puerto
Rican Soils
Rebecca Lindner

2. Introduction
• Metal oxides and recalcitrant carbon
• Ferric iron +  Ferrous iron
(Reduction)
• Fe3+ as an electron sink for C oxidation
• Carbon and Nutrient cycling in the
tropics
• Aerobic and anaerobic microorganisms
(Dubinsky 2012)

3. Hypothesis
• Carbon dioxide production will be slightly
lower in anoxic conditions due to the higher
energy required to use iron (III) as an electron
shuttle in comparison to oxygen.
• In addition, in oscillating environments carbon
dioxide production will increase over time
more quickly than in non-oscillating anoxic
environments.

4. Methods
• 4 Different Cycles were compared
– 3 day anoxic/12 hour oxic
– 6 day anoxic/24 hour oxic
– Full anoxic
– Full oxic
• Soils were buffered with 10 mM MES, 2.04 mM
KCl solution at pH 5.5
• Initially each cycle had 4 trials
• Samples were taken for Iron (II) levels 4 times
corresponding with carbon dioxide samples
(Results pending)

5. Carbon Dioxide Sampling
1. GC vials (2 mL) purged
with nitrogen and capped
2. Three 2 mL gas samples
were taken at equal
intervals (5/10 minutes)
using a 3 mL syringe
3. Samples were brought to
the LI-6400-09
4. A half mL was injected
into the machine
5. An integral was recorded
for each sample which
was compared to a
standard curve

6. Results 75
Initial Carbon Dioxide Flux of Oxic Soils
70
ppm 1mol 1L
Carbon Dioxide (ppm)
* * * 65
1,000,000mol 24.15L 1000mL
60
1000mmol y = 0.038x + 57.12
* headspacemL 55
R² = 0.199
1mol
totalmmols 1 1000000nmol 50
* *
time(min) soil ( g ) 1mmol 45
0 5 10 15 20 25
Time (mins)
Initial Carbon Dioxide Flux of Anoxic Soils
75
Flux = .0406 nmol/g(soil)*min
70
Carbon Dioxide(ppm)
65
60
55
50 y = 0.049x + 47.59
R² = 0.980
45
0 5 10 15 20 25
Time (mins)

7. Carbon Dioxide Flux of Anoxic Soils Carbon Dioxide Flux of 3 Day
after 6 days Oscillated Soil after 6 days (anoxic)
75 75
y = -0.12x + 73.71 y = 0.017x + 71.64
70 R² = 0.481 70 R² = 0.592
Carbon Dioxide (ppm)
Carbon Dioxide (ppm)
65 65
60 60
55 55
50 50
45 45
0 5 10 15 20 25 0 5 10 15 20 25
Time (mins) Time (mins)
Carbon Dioxide Flux of Oxic Soil
after 6 days
75
y = 0.023x + 71.09
70 R² = 0.300
Carbon Dioxide (ppm)
65
60
55
50
45
0 5 10 15 20 25
Time (mins)

8. Carbon Dioxide Flux of Anoxic Soils Carbon Dioxide Flux of 3 Day
after 13 days Oscillated Soil after 13 days (anoxic)
75 75
70 70
Carbon Dioxide (ppm)
Carbon Dioxide (ppm)
65
65
60
60 y = -0.118x + 58.09
55 R² = 0.839
55
y = -0.211x + 55.39 50
R² = 0.855
50
45
45 0 5 10 15 20 25
0 5 10 15 20 25 Time (mins)
Time (mins)
Carbon Dioxide Flux of 6 Day Carbon Dioxide Flux of Oxic Soil after
Oscillated Soil after 13 days (anoxic) 13 days
75
75
70
70 Carbon Dioxide (ppm)
Carbon Dioxide (ppm)
65 65
60 60
y = 0.027x + 57.48
R² = 0.007 55
55 y = -0.055x + 53.72
R² = 0.025
50 50
45 45
0 5 10 15 20 25 0 5 10 15 20 25
Time (mins) Time (mins)

9. Conclusion
• Data still forth coming
• May need to make a few adjustments to
obtain better data
– Longer intervals between flux sampling
– Weighing after each iron sample
– Better containers or use lids without septum
when not taking measurements
– Take first gas sample at time 0
– Follow “USDA-ARS GRACEnet Project Protocols”

10. Special Thanks to
• Dr. Thompson
• Dr. Bertrand
• Dr. Cruz
• Megan
• Peter
• Jared
• Nehru

11. Works Cited!
Dubinsky, Eric A., Silver, Whendee L. and Firestone, Mary
K. "Tropical Forest Soil Microbial Communities Couple
Iron And Carbon Biogeochemistry." Ecology 91.9
(2010): 2604-2612. Academic Search Complete. Web.
10 Apr. 2012.
USDA-ARS GRACEnet Project Protocols -
<http://www.ars.usda.gov/SP2UserFiles/person/31831
/2011%20Parkin%20and%20Venterea%20Trace%20Gas
%20Protocol%20Revision%20Final.pdf>