Reducing conditions, reactive metals, and their interactions can explain spatial patterns of surface soil carbon in a humid tropical forest

Hall, Steven J.; Silver, Whendee L.

doi:10.1007/s10533-015-0120-5

Cited by 89 publications

(117 citation statements)

References 68 publications

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“…Alluvium wetland Fe concentrations were similar (21.76 ± 5.88 mg Fe/g soil; n = 30), demonstrating that Fe concentrations were within the range where microbial Fe reduction inhibits methanogenesis. In contrast to upland humid tropical forests where most Fe is found in poorly crystalline form (Dubinsky et al., ; Hall & Silver, ; Yang & Liptzin, ), poorly crystalline Fe concentrations were roughly two orders of magnitude lower than the HCl‐extractable Fe pool across the wetland sites. Poorly crystalline Fe pools are readily reducible by soil microbes (Hall & Silver, ; Hyacinthe et al., ), and depletion of these pools suggests high activity by microbial Fe reducers in wetland soils (Weiss, Emerson, & Megonigal, ).…”

Section: Discussionmentioning

confidence: 79%

“…The HCl extraction solubilizes reactive Fe 3+ minerals and absorbed/solid Fe 2+ and is used to quantify oxidized (Fe 3+ ) and reduced (Fe 2+ ) Fe pools. The low pH of HCl prevents any Fe 2+ oxidation after the samples are collected (Hall & Silver, ). Roughly 3 g of sample (dry mass equivalent) was immediately placed into preweighed bottles with the HCl solution, and once back in the lab, samples were reweighed, vortexed, shaken for 1 hr, and centrifuged for 10 min at 1,000 rcf.…”

Section: Methodsmentioning

confidence: 99%

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Soil properties and sediment accretion modulate methane fluxes from restored wetlands

Chamberlain

Anthony

Silver

et al. 2018

Global Change Biology

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Wetlands are the largest source of methane (CH ) globally, yet our understanding of how process-level controls scale to ecosystem fluxes remains limited. It is particularly uncertain how variable soil properties influence ecosystem CH emissions on annual time scales. We measured ecosystem carbon dioxide (CO ) and CH fluxes by eddy covariance from two wetlands recently restored on peat and alluvium soils within the Sacramento-San Joaquin Delta of California. Annual CH fluxes from the alluvium wetland were significantly lower than the peat site for multiple years following restoration, but these differences were not explained by variation in dominant climate drivers or productivity across wetlands. Soil iron (Fe) concentrations were significantly higher in alluvium soils, and alluvium CH fluxes were decoupled from plant processes compared with the peat site, as expected when Fe reduction inhibits CH production in the rhizosphere. Soil carbon content and CO uptake rates did not vary across wetlands and, thus, could also be ruled out as drivers of initial CH flux differences. Differences in wetland CH fluxes across soil types were transient; alluvium wetland fluxes were similar to peat wetland fluxes 3 years after restoration. Changing alluvium CH emissions with time could not be explained by an empirical model based on dominant CH flux biophysical drivers, suggesting that other factors, not measured by our eddy covariance towers, were responsible for these changes. Recently accreted alluvium soils were less acidic and contained more reduced Fe compared with the pre-restoration parent soils, suggesting that CH emissions increased as conditions became more favorable to methanogenesis within wetland sediments. This study suggests that alluvium soil properties, likely Fe content, are capable of inhibiting ecosystem-scale wetland CH flux, but these effects appear to be transient without continued input of alluvium to wetland sediments.

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Section: Discussionmentioning

confidence: 79%

Section: Methodsmentioning

confidence: 99%

Soil properties and sediment accretion modulate methane fluxes from restored wetlands

Chamberlain

Anthony

Silver

et al. 2018

Global Change Biology

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“…Soil was sampled from a tropical montane forest in the Luquillo Experimental Forest, Puerto Rico (Bisley Watershed), with 3500 mm of annual precipitation and mean annual temperature of 22 C (Hall and Silver, 2015). This Aquic Hapludox was derived from volcaniclastic sediments and contained substantial short-rangeorder Fe oxides (24 mg Fe g À1 ) and Fe(II) (0.2e0.8 mg g À1 ).…”

Section: Introductionmentioning

confidence: 99%

Iron addition to soil specifically stabilized lignin

Hall

Silver

Timokhin

et al. 2016

Soil Biology and Biochemistry

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a b s t r a c tThe importance of lignin as a recalcitrant constituent of soil organic matter (SOM) remains contested. Associations with iron (Fe) oxides have been proposed to specifically protect lignin from decomposition, but impacts of Fe-lignin interactions on mineralization rates remain unclear. Oxygen (O 2 ) fluctuations characteristic of humid tropical soils drive reductive Fe dissolution and precipitation, facilitating multiple types of Fe-lignin interactions that could variably decompose or protect lignin. We tested impacts of Fe addition on 13 C methoxyl-labeled lignin mineralization in soils that were exposed to static or fluctuating O 2 . Iron addition suppressed lignin mineralization to 21% of controls, regardless of O 2 availability. However, Fe addition had no effect on soil CO 2 production, implying that Fe oxides specifically protected lignin methoxyls but not bulk SOM. Iron oxide-lignin interactions represent a specific mechanism for lignin stabilization, linking SOM biochemical composition to turnover via geochemistry.

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“…Surface soil (0–10 cm) was collected from the Luquillo Experimental Forest, Puerto Rico, for incubation experiments. This ecosystem is a montane, per‐humid tropical forest with mean annual precipitation of 3800 mm year −1 and temperature of 24°C, and is described in detail elsewhere . The soil is a clay‐rich Oxisol formed from volcaniclastic sediments with C and N content of 34.1 and 3.0 mg g −1 , respectively.…”

Section: Methodsmentioning

confidence: 99%

An optical method for carbon dioxide isotopes and mole fractions in small gas samples: Tracing microbial respiration from soil, litter, and lignin

Hall

Huang

Hammel

2017

Rapid Comm Mass Spectrometry

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Rationale Carbon dioxide isotope (δ13C value) measurements enable quantification of the sources of soil microbial respiration, thus informing ecosystem C dynamics. Tunable diode lasers (TDLs) can precisely measure CO2 isotopes at low cost and high throughput, but are seldom used for small samples (≤5 mL). We developed a TDL method for CO2 mole fraction ([CO2]) and δ13C analysis of soil microcosms. Methods Peaks in infrared absorbance following constant volume sample injection to a carrier were used to independently measure [12CO2] and [13CO2] for subsequent calculation of δ13C values. Using parallel soil incubations receiving differing C substrates, we partitioned respiration from three sources using mixing models: native soil organic matter (SOM), added litter, and synthetic lignin containing a 13C label at Cβ of the propyl side chain. Results Once‐daily TDL calibration enabled accurate quantification of δ13C values and [CO2] compared with isotope ratio mass spectrometry (IRMS), with long‐term external precision of 0.17 and 0.31‰ for 5 and 1 mL samples, respectively, and linear response between 400 and 5000 μmol mol−1 CO2. Production of CO2 from native soil C, added litter, and lignin Cβ varied over four orders of magnitude. Multiple‐pool first‐order decay models fitted to data (R2 > 0.98) indicated substantially slower turnover for lignin Cβ (17 years) than for the dominant pool of litter (1.3 years) and primed soil C (3.9 years). Conclusions Our TDL method provides a flexible, precise, and high‐throughput (60 samples h−1) alternative to IRMS for small samples. This enables the use of C isotopes in increasingly sophisticated experiments to test biogeochemical controversies, such as the fate of lignins in soil.

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Reducing conditions, reactive metals, and their interactions can explain spatial patterns of surface soil carbon in a humid tropical forest

Cited by 89 publications

References 68 publications

Soil properties and sediment accretion modulate methane fluxes from restored wetlands

Soil properties and sediment accretion modulate methane fluxes from restored wetlands

Iron addition to soil specifically stabilized lignin

An optical method for carbon dioxide isotopes and mole fractions in small gas samples: Tracing microbial respiration from soil, litter, and lignin

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