Continental-scale controls on soil organic carbon across sub-Saharan Africa

Fromm, Sophie F. von; Hoyt, Alison M.; Lange, Markus; Aynekulu, Ermias; Berhe, Asmeret Asefaw; Haefele, S. M.; McGrath, Steve P.; Sila, Andrew; Six, Johan; Towett, Erick K.; Trumbore, Susan E.; Vågen, Tor-Gunnar; Weullow, Elvis; Winowiecki, Leigh A.; Doetterl, Sebastian

doi:10.5194/soil-7-305-2021

Cited by 48 publications

(44 citation statements)

References 74 publications

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“…In our study, a diverse suite of variables was selected for predicting SOM vulnerability to mineralization. Consistent with previous large-scale studies of SOC (Doetterl et al 2015;Rasmussen et al 2018;Viscarra Rossel et al 2019;von Fromm et al 2021;Yu et al 2021), this varied group of predictors illustrates how numerous factors control SOM dynamics at large (i.e., continental) scales. The variables selected generally fall into three broad categories related to (1) SOM chemistry, (2) reactive Fe and Al phases, and (3) site moisture availability (Table 4; Figs.…”

Section: Som Vulnerability To Mineralization Predicted By Diverse Suite Of Variablessupporting

confidence: 87%

“…However, the paradigm that has emerged over the past decade places less emphasis on the chemical properties of SOM in mineral soils. Instead, it posits that soil physicochemical properties (e.g., pH, abundance of reactive metals and divalent cations) and other ecosystem properties (e.g., vegetation, climate) are the dominant factors controlling SOM stabilization (Rasmussen et al 2018;Kramer and Chadwick 2018;von Fromm et al 2021;Yu et al 2021). With this paradigm shift, a broad suite of stabilization mechanisms has been identified, including: (1) occlusion within aggregates, (2) mineral-organic matter interactions, (3) formation of pyrogenic C, (4) biotic suppression due to climatic factors (e.g., xeric conditions, extreme temperatures), and (5) biotic suppression due to local environmental conditions (e.g., low O 2 levels) (von Lu ¨tzow et al 2006;Schmidt et al 2011;Rasmussen et al 2018;Wiesmeier et al 2019).…”

Section: Introductionmentioning

confidence: 99%

“…and Mg 2? ) and reactive (Fe) and aluminum (Al) (Rasmussen et al 2018;Kramer and Chadwick 2018;von Fromm et al 2021;Yu et al 2021). This reflects an implicit assumption that mineral-organic matter interactions are the primary stabilization mechanism in mineral soils across different ecosystems.…”

Section: Introductionmentioning

confidence: 99%

“…Most recent large-scale studies of SOM have focused on measuring SOC concentration (Rasmussen et al 2018;von Fromm et al 2021;Quesada et al 2020;Yu et al 2021), SOC stocks (Nave et al 2021, or certain SOC pools (Kramer and Chadwick 2018;Viscarra Rossel et al 2019). Although these measures provide valuable insights into soil C cycling, they provide an incomplete picture of SOM dynamics.…”

Section: Introductionmentioning

confidence: 99%

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Key predictors of soil organic matter vulnerability to mineralization differ with depth at a continental scale

et al. 2021

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Soil organic matter (SOM) is the largest terrestrial pool of organic carbon, and potential carbon-climate feedbacks involving SOM decomposition could exacerbate anthropogenic climate change. However, our understanding of the controls on SOM mineralization is still incomplete, and as such, our ability to predict carbon-climate feedbacks is limited. To improve our understanding of controls on SOM decomposition, A and upper B horizon soil samples from 26 National Ecological Observatory Network (NEON) sites spanning the conterminous U.S. were incubated for 52 weeks under conditions representing site-specific mean summer temperature and sample-specific field capacity (−33 kPa) water potential. Cumulative carbon dioxide respired was periodically measured and normalized by soil organic C content to calculate cumulative specific respiration (CSR), a metric of SOM vulnerability to mineralization. The Boruta algorithm, a feature selection algorithm, was used to select important predictors of CSR from 159 variables. A diverse suite of predictors was selected (12 for A horizons, 7 for B horizons) with predictors falling into three categories corresponding to SOM chemistry, reactive Fe and Al phases, and site moisture availability. The relationship between SOM chemistry predictors and CSR was complex, while sites that had greater concentrations of reactive Fe and Al phases or were wetter had lower CSR. Only three predictors were selected for both horizon types, suggesting dominant controls on SOM decomposition differ by horizon. Our findings contribute to the emerging consensus that a broad array of controls regulates SOM decomposition at large scales and highlight the need to consider changing controls with depth.

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Section: Som Vulnerability To Mineralization Predicted By Diverse Suite Of Variablessupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Key predictors of soil organic matter vulnerability to mineralization differ with depth at a continental scale

et al. 2021

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“…This adds to the existing literature suggesting that nutrient limitation, especially N and P, can significantly inhibit microbial growth and activity, hence lowering soil C turnover rates (Fang et al, 2014;Kunito et al, 2009). In addition, the depletion of N and high C : N values (153.9 ± 68.5) of fossil organic C, which encompasses a substantial part of total C in subsoils of the mixed sediment region (Table 2), was likely an additional factor reducing soil respiration rates (Whitaker et al, 2014). However, respiration rates in the topsoil of the mixed sediment were also lower compared to the mafic or felsic region (Fig.…”

Section: Fertility and Microbial Activitymentioning

confidence: 60%

Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

Bukombe

Fiener

Hoyt

et al. 2021

SOIL

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Abstract. Heterotrophic soil respiration is an important component of the global terrestrial carbon (C) cycle, driven by environmental factors acting from local to continental scales. For tropical Africa, these factors and their interactions remain largely unknown. Here, using samples collected along topographic and geochemical gradients in the East African Rift Valley, we study how soil chemistry and fertility drive soil respiration of soils developed from different parent materials even after many millennia of weathering. To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic and mixed sediment) sampled along slope gradients. For three soil depths, we measured the potential maximum heterotrophic respiration under stable environmental conditions and the radiocarbon content (Δ14C) of the bulk soil and respired CO2. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. We found that soil microorganisms were able to mineralize soil C from a variety of sources and with variable C quality under laboratory conditions representative of tropical topsoil. However, in the presence of organic carbon sources of poor quality or the presence of strong mineral-related C stabilization, microorganisms tend to discriminate against these energy sources in favour of more accessible forms of soil organic matter, resulting in a slower rate of C cycling. Furthermore, despite similarities in climate and vegetation, soil respiration showed distinct patterns with soil depth and parent material geochemistry. The topographic origin of our samples was not a main determinant of the observed respiration rates and Δ14C. In situ, however, soil hydrological conditions likely influence soil C stability by inhibiting decomposition in valley subsoils. Our results demonstrate that, even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks and the turnover of C in soil. Soil parent material and its control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.

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What do relationships between extractable metals and soil organic carbon concentrations mean?

Hall

Thompson

2022

Soil Science Soc of Amer J

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Aluminum (Al)‐bearing and iron (Fe)‐bearing minerals, especially short‐range‐ordered (SRO) phases, are thought to protect soil organic C (SOC). However, it remains methodologically challenging to assess the influence of Al vs. Fe minerals or metal complexes. Whereas SRO Al and Fe phases share some properties, Al dissolved by oxalate (Alox) often correlates stronger with SOC than Fe dissolved by oxalate (Feox) or citrate–dithionite (Fecd). To further evaluate these relationships, we analyzed a large North American soil dataset from the National Ecological Observatory Network. A strong relationship between Alox and SOC (and weaker Feox‐SOC relationship) persisted even after excluding soils rich in SRO minerals (Andisols and Spodosols). Al dissolved by oxalate was strongly correlated with citrate–dithionite‐extractable Al (Alcd; slope = 0.92, R2 = .69), and discrepancies could be explained (R2 = .87) by greater dissolution of Al‐substituted Fe phases by citrate–dithionite and greater dissolution of aluminosilicates by oxalate. Aluminum dissolved by oxalate and Alcd were both strong SOC predictors despite their differing relationships with silicon (Si). Al dissolved by oxalate and Siox strongly covaried (R2 = .79), but Alcd was inconsistently related to Sicd (R2 = .18). Similar relationships of Alox and Alcd with SOC, despite differences in minerals extracted by oxalate and citrate–dithionite, suggest that Al‐OC complexes (as opposed to aluminosilicate or iron‐bearing minerals) were the best SOC predictor. This raises important questions: do Al‐OC complexes indicate protection from decomposition or simply reflect greater intensity of mineral weathering by organic acids; and, if the latter, then perhaps SOC input is driving Alox and SOC correlations rather than Al phase composition or abundance.

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Continental-scale controls on soil organic carbon across sub-Saharan Africa

Cited by 48 publications

References 74 publications

Key predictors of soil organic matter vulnerability to mineralization differ with depth at a continental scale

Key predictors of soil organic matter vulnerability to mineralization differ with depth at a continental scale

Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

What do relationships between extractable metals and soil organic carbon concentrations mean?

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