Hot Spots and Hot Moments of Soil Moisture Explain Fluctuations in Iron and Carbon Cycling in a Humid Tropical Forest Soil

Barcellos, Diego; O’Connell, Christine; Silver, Whendee L.; Meile, Christof; Thompson, Aaron

doi:10.3390/soilsystems2040059

Cited by 48 publications

(38 citation statements)

References 73 publications

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“…where E a is the activation energy, A is the pre-exponential factor, R is the universal gas constant (8.314 J K −1 mol −1 ), and T is temperature in kelvin (K). Relationships between total C and biogeochemical parameters were analyzed using linear mixed-effects models with the lme4 package (Bates et al, 2015) in Rstudio. Regression analyses were conducted for the entire year-long dataset and for the growing and nongrowing seasons defined as May through September and October through March, respectively.…”

Section: Statistical Analysesmentioning

confidence: 99%

“…A recent study along hillslope transects in tropical forest soils representing an oxygen gradient (Hall and Silver, 2015), for example, found that a combination of Fe (II) (a proxy for reducing conditions), fine root biomass, and total Fe and Al concentrations explained the most variation of surface soil C content. How the relationships between C and important biogeochemical controls differ in systems that are subject to seasonal flooding is still in question, especially with depth (Barcellos et al, 2018).…”

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confidence: 99%

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Shifting mineral and redox controls on carbon cycling in seasonally flooded mineral soils

et al. 2019

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Abstract. Although wetland soils represent a relatively small portion of the terrestrial landscape, they account for an estimated 20 %–30 % of the global soil carbon (C) reservoir. C stored in wetland soils that experience seasonal flooding is likely the most vulnerable to increased severity and duration of droughts in response to climate change. Redox conditions, plant root dynamics, and the abundance of protective mineral phases are well-established controls on soil C persistence, but their relative influence in seasonally flooded mineral soils is largely unknown. To address this knowledge gap, we assessed the relative importance of environmental (temperature, soil moisture, and redox potential) and biogeochemical (mineral composition and root biomass) factors in controlling CO2 efflux, C quantity, and organic matter composition along replicated upland–lowland transitions in seasonally flooded mineral soils. Specifically, we contrasted mineral soils under temperature deciduous forests in lowland positions that undergo seasonal flooding with adjacent upland soils that do not, considering both surface (A) and subsurface (B and C) horizons. We found the lowland soils had lower total annual CO2 efflux than the upland soils, with monthly CO2 efflux in lowlands most strongly correlated with redox potential (Eh). Lower CO2 efflux as compared to the uplands corresponded to greater C content and abundance of lignin-rich, higher-molecular-weight, chemically reduced organic compounds in the lowland surface soils (A horizons). In contrast, subsurface soils in the lowland position (Cg horizons) showed lower C content than the upland positions (C horizons), coinciding with lower abundance of root biomass and oxalate-extractable Fe (Feo, a proxy for protective Fe phases). Our linear mixed-effects model showed that Feo served as the strongest measured predictor of C content in upland soils, yet Feo had no predictive power in lowland soils. Instead, our model showed that Eh and oxalate-extractable Al (Alo, a proxy of protective Al phases) became significantly stronger predictors in the lowland soils. Combined, our results suggest that low redox potentials are the primary cause for C accumulation in seasonally flooded surface soils, likely due to selective preservation of organic compounds under anaerobic conditions. In seasonally flooded subsurface soils, however, C accumulation is limited due to lower C inputs through root biomass and the removal of reactive Fe phases under reducing conditions. Our findings demonstrate that C accrual in seasonally flooded mineral soil is primarily due to low redox potential in the surface soil and that the lack of protective metal phases leaves these C stocks highly vulnerable to climate change.

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Section: Statistical Analysesmentioning

confidence: 99%

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confidence: 99%

Shifting mineral and redox controls on carbon cycling in seasonally flooded mineral soils

et al. 2019

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“…Tropical wet forest ecosystems are characterized by year‐round precipitation and pronounced seasonality, with drier periods still receiving more than 60 mm per month. Soil CO 2 concentrations in tropical soils can change markedly on weekly, monthly, and seasonal timescales, with substantially higher soil CO 2 levels in wet versus drier periods (Barcellos, O'Connell, Silver, Meile, & Thompson, 2018; Fernandez‐Bou et al, 2018; O'Connell, Ruan, & Silver, 2018; Schwendenmann & Veldkamp, 2006; Schwendenmann, Veldkamp, Brenes, O'Brien, & Mackensen, 2003). For wet rainforest soils in Costa Rica, Schwendenmann and Veldkamp (2006) reported that 75% of the CO 2 production occurred in the upper 0.5 m of the soil profile, attributing this to the lack of water stress and related shallow root biomass distribution.…”

Section: Introductionmentioning

confidence: 99%

“…However, after this initial increase, the damage in the canopy may lead to the opposite effect, and may open the soil to drying and to large diurnal variations in soil CO 2 respiration (Vargas & Allen, 2008a); this is a major driver of the nitrogen cycling and belowground carbon dynamics (Hasselquist, Santiago, & Allen, 2010). Regardless of mechanisms, short‐term fluctuations in soil CO 2 concentrations (and other greenhouse gases) lead to variability in soil emissions (Barcellos et al., 2018; Fernandez‐Bou, Dierick, & Harmon, 2020; Fernandez‐Bou et al, 2018; Harms & Grimm, 2008; Haverd, Ahlström, Smith, & Canadell, 2017; Kuzyakov & Blagodatskaya, 2015; Leon et al., 2014; Lubbers, Berg, Deyn, van der Putten, & van Groenigen, 2019; Soper et al., 2019; Swanson et al., 2019; Vargas et al., 2018). In this work, we monitor soil CO 2 concentration over multiple years to better understand its short‐term dynamics and potential influence on tropical soil CO 2 emissions.…”

Section: Introductionmentioning

confidence: 99%

Precipitation‐drainage cycles lead to hot moments in soil carbon dioxide dynamics in a Neotropical wet forest

Fernandez‐Bou

Dierick

Allen

et al. 2020

Global Change Biology

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Soil CO 2 concentrations and emissions from tropical forests are modulated seasonally by precipitation. However, subseasonal responses to meteorological events (e.g., storms, drought) are less well known. Here, we present the effects of meteorological variability on short-term (hours to months) dynamics of soil CO 2 concentrations and emissions in a Neotropical wet forest. We continuously monitored soil

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“…The timescales of oxic and anoxic conditions, which are so crucial for the Fe redox dynamics previously discussed, are then intimately linked to the fluctuations in soil water content, which controls the diffusion of O 2 (Brady & Weil, 2016). Experimental evidence (Barcellos, O'Connell, et al, 2018;Hall et al, 2013) indeed suggests that, at the time scales of interest here, oxygen content is strongly related to the level of soil moisture, the former remaining high (≈20%) for water contents up to the so-called field capacity and then rapidly declining to ≈0% at saturation, when microbes and labile C exist to stimulate O 2 consumption (Keiluweit et al, 2018;Parkin, 1987;Silver et al, 1999). Soil moisture dynamics are linked to the soil, plant, and atmospheric conditions; the frequency and depth of rainfall events, evapotranspiration from soil and plants, and soil properties jointly determine the temporal evolution of soil oxic and anoxic conditions.…”

Section: Linking Oxic/anoxic Cycles To Rainfall Frequency and Intensimentioning

confidence: 99%

Theoretical Constraints on Fe Reduction Rates in Upland Soils as a Function of Hydroclimatic Conditions

et al. 2020

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Periods of high soil wetness promote anaerobic processes such as iron (Fe) reduction within soil microsites, with implications for organic matter decomposition, the fate of pollutants, and nutrient cycling. Here we discuss potential Fe reduction rates emerging from an interplay between the timescales of the internal reactions (Fe oxidation and reduction) and external forcings (length of oxic vs. anoxic conditions), and under no organic substrate and microbial population limitations. We compute the upper bound on Fe reduction and the theoretical maximum reduction rate, which would be reached under “resonant conditions,” whereby the timescales of external forcings match the internal timescales of the redox reactions. The variability of soil oxygen is then linked to rainfall frequency and intensity through soil moisture dynamics, allowing us to determine the hydroclimatic conditions that generate oxic/anoxic cycles that most favor Fe reduction. These predictions are applied to an aseasonal tropical (Luquillo, Puerto Rico, USA) and a seasonal subtropical (Calhoun, SC, USA) humid forests. We show that the tropical site maintains a high potential for Fe reduction throughout the year, due to rapid and frequent transitions between predicted oxic and anoxic microsite conditions, with a potential to reduce up to 1,800 mmol kg−1 soil of Fe per year, while a less humid and seasonal climate in the subtropical site limits maximum reduction rates to 60 mmol kg−1 year−1. This analysis paves the way for a global identification of hot spots of potential Fe reduction using readily available hydroclimatic observations.

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Hot Spots and Hot Moments of Soil Moisture Explain Fluctuations in Iron and Carbon Cycling in a Humid Tropical Forest Soil

Cited by 48 publications

References 73 publications

Shifting mineral and redox controls on carbon cycling in seasonally flooded mineral soils

Shifting mineral and redox controls on carbon cycling in seasonally flooded mineral soils

Precipitation‐drainage cycles lead to hot moments in soil carbon dioxide dynamics in a Neotropical wet forest

Theoretical Constraints on Fe Reduction Rates in Upland Soils as a Function of Hydroclimatic Conditions

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