1) The study measured carbon dioxide production from Puerto Rican soils under different redox conditions to understand the role of iron in carbon cycling.
2) Four treatment cycles were compared: 3 day anoxic/12 hour oxic, 6 day anoxic/24 hour oxic, fully anoxic, and fully oxic. Soil samples were taken over time to measure carbon dioxide and pending iron levels.
3) Preliminary results showed carbon dioxide production was initially higher in oxic soils but decreased more over time in anoxic soils, supporting the hypothesis that iron cycling plays a role in prolonged carbon dioxide production during alternating redox conditions.
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
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>