Faster redox fluctuations can lead to higher iron reduction rates in humid forest soils
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Iron (Fe) minerals play an important role in carbon (C) and nutrient dynamics in redox fluctuating soils. We explored how the frequency of redox oscillations influence Fe reduction rates and C content in Puerto Rican soils. We hypothesized that iron reduction rates would be faster during short oscillation periods than in longer oscillation periods. Surface soils from an upland valley in a humid tropical forest were exposed to systematic redox oscillations over 49 days. The oxidation events were triggered by the introduction of air (21% O2), maintaining the time ratio under oxic or anoxic conditions at 1:6 (τox/τanox). After pre-conditioning the soil to fluctuating redox conditions for 1 month, we imposed 280- and 70-h (or 11.67- and 2.5-day) redox oscillations, measuring FeII every few days. We found that by the end of the experiment, Fe reduction rates were higher in the short oscillation period (τox = 10 h, τanox = 60 h) than in the long oscillation period (τox = 40 h, τanox = 240 h). Carbon and nitrogen loss however was similar for both treatments. These results suggest the characteristics of redox fluctuations can alter rates of Fe reduction and potentially influence ecosystem processes that depend on iron behavior.
KeywordsIron Carbon Tropical forest soil Redox oscillations
Thanks for scholarship support from the CAPES Foundation, Ministry of Education of Brazil to DB. We thank Whendee Silver for providing field samples, Allan Bacon and Julio Pachon for conducting soil texture analysis, and members of the Thompson Lab (especially Jared Wilmoth) for technical assistance. We also thank two annoymous reviewers and the associate editor whose helpful comments greatly improved the manuscript.
Funding for this research was provided by National Science Foundation (NSF), Grants EAR-1331841, EAR-1331846, EAR-1451508 and DEB-1457761 to AT.
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