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Title: Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils

Abstract

Oscillating redox conditions are the norm in tropical soils; driven by an ample supply of reductants, high moisture, microbial oxygen consumption, and finely textured clays that limit diffusion. Yet the net result of variable soil redox regimes--their effect on biogeochemical fluxes, and susceptibility to environmental change--is poorly understood in tropical soils. Using a 44-day redox incubation experiment with humid tropical soils from Puerto Rico, we examined patterns of Fe and C transformations under four redox regimes: static anoxic, ‘flux 4-day’ (4d oxic, 4d anoxic), ‘flux 8-day’ (8d oxic, 4d anoxic) and static anoxic. Prolonged anoxia promoted reductive dissolution of Fe-oxides, and lead to an increase in soluble Fe(II) and amorphous Fe oxide pools. Preferential dissolution of the less-crystalline Fe pool was evident immediately following a shift in bulk redox status (oxic to anoxic), and coincided with increased dissolved organic carbon, presumably due to acidification or direct release of OM from dissolving Fe(III) mineral phases. The average nominal oxidation state of water-soluble carbon was lowest under persistent anoxic conditions, suggesting that more reduced organic compounds were metabolically unavailable for microbial consumption under reducing conditions. Anoxic soil compounds had high H/C values (and were similar to lignin-like compounds) whereas oxic soil compoundsmore » had higher O/C values, akin to tannin- and cellulose-like components. Cumulative respiration derived from native soil organic carbon was highest in static oxic soils. These results highlight the volatility of mineral-OM interactions in tropical soils. They suggest that shifting soil O 2 availability has rapid impacts on exchanges between mineral-sorbed and aqueous C pools, accelerates the turnover of carbon, and changes available OM composition, implying that the periodicity of low-redox moments may control the fate of C in wet tropical soils.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5]; ORCiD logo [2]
  1. Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States; Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
  2. Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
  3. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
  4. Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, California 94720, United States
  5. Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1497008
Report Number(s):
PNNL-SA-135734
Journal ID: ISSN 0013-936X
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 52; Journal Issue: 24; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English

Citation Formats

Bhattacharyya, Amrita, Campbell, Ashley N., Tfaily, Malak M., Lin, Yang, Kukkadapu, Ravi K., Silver, Whendee L., Nico, Peter S., and Pett-Ridge, Jennifer. Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils. United States: N. p., 2018. Web. doi:10.1021/acs.est.8b03408.
Bhattacharyya, Amrita, Campbell, Ashley N., Tfaily, Malak M., Lin, Yang, Kukkadapu, Ravi K., Silver, Whendee L., Nico, Peter S., & Pett-Ridge, Jennifer. Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils. United States. doi:10.1021/acs.est.8b03408.
Bhattacharyya, Amrita, Campbell, Ashley N., Tfaily, Malak M., Lin, Yang, Kukkadapu, Ravi K., Silver, Whendee L., Nico, Peter S., and Pett-Ridge, Jennifer. Mon . "Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils". United States. doi:10.1021/acs.est.8b03408.
@article{osti_1497008,
title = {Redox Fluctuations Control the Coupled Cycling of Iron and Carbon in Tropical Forest Soils},
author = {Bhattacharyya, Amrita and Campbell, Ashley N. and Tfaily, Malak M. and Lin, Yang and Kukkadapu, Ravi K. and Silver, Whendee L. and Nico, Peter S. and Pett-Ridge, Jennifer},
abstractNote = {Oscillating redox conditions are the norm in tropical soils; driven by an ample supply of reductants, high moisture, microbial oxygen consumption, and finely textured clays that limit diffusion. Yet the net result of variable soil redox regimes--their effect on biogeochemical fluxes, and susceptibility to environmental change--is poorly understood in tropical soils. Using a 44-day redox incubation experiment with humid tropical soils from Puerto Rico, we examined patterns of Fe and C transformations under four redox regimes: static anoxic, ‘flux 4-day’ (4d oxic, 4d anoxic), ‘flux 8-day’ (8d oxic, 4d anoxic) and static anoxic. Prolonged anoxia promoted reductive dissolution of Fe-oxides, and lead to an increase in soluble Fe(II) and amorphous Fe oxide pools. Preferential dissolution of the less-crystalline Fe pool was evident immediately following a shift in bulk redox status (oxic to anoxic), and coincided with increased dissolved organic carbon, presumably due to acidification or direct release of OM from dissolving Fe(III) mineral phases. The average nominal oxidation state of water-soluble carbon was lowest under persistent anoxic conditions, suggesting that more reduced organic compounds were metabolically unavailable for microbial consumption under reducing conditions. Anoxic soil compounds had high H/C values (and were similar to lignin-like compounds) whereas oxic soil compounds had higher O/C values, akin to tannin- and cellulose-like components. Cumulative respiration derived from native soil organic carbon was highest in static oxic soils. These results highlight the volatility of mineral-OM interactions in tropical soils. They suggest that shifting soil O2 availability has rapid impacts on exchanges between mineral-sorbed and aqueous C pools, accelerates the turnover of carbon, and changes available OM composition, implying that the periodicity of low-redox moments may control the fate of C in wet tropical soils.},
doi = {10.1021/acs.est.8b03408},
journal = {Environmental Science and Technology},
issn = {0013-936X},
number = 24,
volume = 52,
place = {United States},
year = {2018},
month = {11}
}