Iron Redox Reactions Can Drive Microtopographic Variation in Upland Soil Carbon Dioxide and Nitrous Oxide Emissions

Alexander H. Krichels,Emina Sipic,Wendy H. Yang

doi:10.3390/soilsystems3030060

Alexander H. Krichels, Emina Sipic + Show 1 more

Open Access

https://doi.org/10.3390/soilsystems3030060

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Abstract

Topographic depressions in upland soils experience anaerobic conditions conducive for iron (Fe) reduction following heavy rainfall. These depressional areas can also accumulate reactive Fe compounds, carbon (C), and nitrate, creating potential hot spots of Fe-mediated carbon dioxide (CO2) and nitrous oxide (N2O) production. While there are multiple mechanisms by which Fe redox reactions can facilitate CO2 and N2O production, it is unclear what their cumulative effect is on CO2 and N2O emissions in depressional soils under dynamic redox. We hypothesized that Fe reduction and oxidation facilitate greater CO2 and N2O emissions in depressional compared to upslope soils in response to flooding. To test this, we amended upslope and depressional soils with Fe(II), Fe(III), or labile C and measured CO2 and N2O emissions in response to flooding. We found that depressional soils have greater Fe reduction potential, which can contribute to soil CO2 emissions during flooded conditions when C is not limiting. Additionally, Fe(II) addition stimulated N2O production, suggesting that chemodenitrification may be an important pathway of N2O production in depressions that accumulate Fe(II). As rainfall intensification results in more frequent flooding of depressional upland soils, Fe-mediated CO2 and N2O production may become increasingly important pathways of soil greenhouse gas emissions.

Highlights

Rainfall intensification as a result of global climate change has resulted in the increased ponding of ecosystems that exhibit topography [1,2,3]
While Fe redox reactions are known to occur in upland soils, it is unclear how they contribute to CO2 and nitrous oxide (N2 O)
Soil pH was higher in depressions compared to upslope positions (F2,26 = 50, p < 0.001, Figure 2b); it was lowest in the Energy Farm soils and highest in Cardinal Road soils (F1,26 = 459, p < 0.001)

Summary

Introduction

Rainfall intensification as a result of global climate change has resulted in the increased ponding of ecosystems that exhibit topography [1,2,3]. Iron redox reactions can be coupled to C and N transformations in upland soils via multiple mechanisms (Figure 1) [6,7], contributing to emissions of carbon dioxide (CO2 ) and nitrous oxide (N2 O), two potent greenhouse gases. These reactions could become more prevalent as rainfall intensification increases the ponding extent and duration in upland soils. While Fe redox reactions are known to occur in upland soils, it is unclear how they contribute to CO2 and N2 O emissions in upslope and depressional soils in response to ponding following heavy rainfall

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