Ecosystem type effects on the stabilization of organic matter in soils: Combining size fractionation with sequential chemical extractions

Giannetta, Beatrice; Plaza, César; Zaccone, Claudio; Vischetti, Costantino; Rovira, Pere

doi:10.1016/j.geoderma.2019.07.009

Cited by 29 publications

(25 citation statements)

References 60 publications

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“…Our second approach investigated the stabilisation of mineral-associated SOC using sequential chemical extractions at increasing pH, which enhances the solubility of SOC by promoting the desorption of organic matter from mineral surfaces 30,31 . Here, we use extraction strength to represent the energy requirement by microorganisms to access mineral-associated SOC.…”

Section: Methodsmentioning

confidence: 99%

“…12 solubilizes ‘resistant SOC’ that is strongly bound to active mineral surfaces and is not solubilized by the previous extractions. Finally, a second NaOH extraction after pre-treatment with 0.1 M sodium dithionite reduces the iron in oxides, hydroxides and sesquioxides, thus solubilizing the organic molecules adsorbed to them 30,31 .…”

Section: Methodsmentioning

confidence: 99%

“…by priming effects, has offset the storage of new SOM. We explored these possibilities using sequential chemical extractions 30,31 to assess the distribution of mineral-associated SOC along a gradient of increasing sorption strength (Methods).

Figure 3Changes in the carbon content and mass of soil organic carbon (SOC) fractions at 0–10 cm depth after 13 years of litter addition (L+; triangles) compared to control soils (CT; circles) in a lowland tropical forest soil in Panama, Central America, showing the carbon content (left-hand panels) and the proportion of each fraction relative to the total sample mass (right-hand panels) of ( a ) the accessible SOC fraction (2000–20 μm) and ( b ) the mineral-associated SOC fraction (<20 μm); means and standard errors are shown for n = 4 per treatment; soil mass was corrected for differences in bulk density.…”

Section: Introductionmentioning

confidence: 99%

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Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Sayer

Lopez-Sangil

Crawford

et al. 2019

Sci Rep

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Soil organic carbon (SOC) dynamics represent a persisting uncertainty in our understanding of the global carbon cycle. SOC storage is strongly linked to plant inputs via the formation of soil organic matter, but soil geochemistry also plays a critical role. In tropical soils with rapid SOC turnover, the association of organic matter with soil minerals is particularly important for stabilising SOC but projected increases in tropical forest productivity could trigger feedbacks that stimulate the release of stored SOC. Here, we demonstrate limited additional SOC storage after 13–15 years of experimentally doubled aboveground litter inputs in a lowland tropical forest. We combined biological, physical, and chemical methods to characterise SOC along a gradient of bioavailability. After 13 years of monthly litter addition treatments, most of the additional SOC was readily bioavailable and we observed no increase in mineral-associated SOC. Importantly, SOC with weak association to soil minerals declined in response to long-term litter addition, suggesting that increased plant inputs could modify the formation of organo-mineral complexes in tropical soils. Hence, we demonstrate the limited capacity of tropical soils to sequester additional C inputs and provide insights into potential underlying mechanisms.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Sayer

Lopez-Sangil

Crawford

et al. 2019

Sci Rep

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“…Nitrogen plays a key role in SOM formation (Billings and Ballantyne 2013) because the C:N ratio of organic matter in the early stages of decomposition is higher than the C:N ratio of the microbial biomass, and microbial decomposers therefore require N from supplemental sources (Hessen et al 2004). Indeed, POM that has undergone little decomposition has a C:N ratio similar to plant material (c. 10-40;Fornara et al 2011;Lavallee et al 2020), which declines as decomposition progresses (Khan et al 2016), resulting in MAOM with a C:N ratio similar to microbial biomass (c. 8-13;Giannetta et al 2019;Lavallee et al 2020). As the transformation of plant material into stabilised SOM requires N, the ability of soils to store C is strongly linked to N availability (Kirkby et al 2013;Paul 2016;Cotrufo et al 2019) and N limitation can reduce the microbial contribution to SOM formation (Khan et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…In highly weathered tropical soils, SOM stabilisation is often associated with high concentrations of iron (Fe) and aluminium (Al) oxides, which are capable of binding organic compounds into stable organo-mineral complexes (Coward et al 2017). The formation of organo-mineral complexes by Al and Fe oxyhydroxides often involves nitrogenous compounds (Giannetta et al 2019) which suggests that N availability might also play a key role in SOM stabilisation in tropical soils. Although N availability in lowland tropical soils is often high relative to other nutrients, tropical forest nutrient cycles are also characterized as efficient, and a large proportion of the nutrients required for plant growth is recycled in litterfall (Vitousek 1984).…”

Section: Introductionmentioning

confidence: 99%

Altered litter inputs modify carbon and nitrogen storage in soil organic matter in a lowland tropical forest

et al. 2020

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Soil organic matter (SOM) in tropical forests is an important store of carbon (C) and nutrients. Although SOM storage could be affected by global changes via altered plant productivity, we know relatively little about SOM stabilisation and turnover in tropical forests compared to temperate systems. Here, we investigated changes in soil C and N within particle size fractions representing particulate organic matter (POM) and mineral-associated organic matter (MAOM) after 13 years of experimental litter removal (L−) and litter addition (L+) treatments in a lowland tropical forest. We hypothesized that reduced nitrogen (N) availability in L− plots would result in N-mining of MAOM, whereas long-term litter addition would increase POM, without altering the C:N ratio of SOM fractions. Overall, SOM-N declined more than SOM-C with litter removal, providing evidence of N-mining in the L− plots, which increased the soil C:N ratio. However, contrary to expectations, the C:N ratio increased most in the largest POM fraction, whereas the C:N ratio of MAOM remained unchanged. We did not observe the expected increases in POM with litter addition, which we attribute to rapid turnover of unprotected SOM. Measurements of ion exchange rates to assess changes in N availability and soil chemistry revealed that litter removal increased the mobility of ammonium-N and aluminium, whereas litter addition increased the mobility of nitrate-N and iron, which could indicate SOM priming in both treatments. Our study suggests that altered litter inputs affect multiple processes contributing to SOM storage and we propose potential mechanisms to inform future work.

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Validation and comparisons of NaOH and Na₄P₂O₇ extraction methods for the characterization of organic amendments

Audette

Longstaffe

Gillespie

et al. 2021

Soil Science Soc of Amer J

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The objectives of this study are to compare the chemical properties of organic matter (OM) in alkaline extracts of turkey litter compost, source-separated organic compost and biosolid pellets, and to validate the use of humic acids (HA) for analyzing the functionality, i.e., the ability to complex with nutrients, of OM. The humic fractions, including humic acids (HA), fulvic acids (FA) and alkaline non-dissolved fraction (humin), were isolated either with NaOH or Na 4 P 2 O 7 (PyroP) and the chemical properties were analyzed by solid-state 13 C NMR spectroscopy. The study showed that the proportions of each functional group of the combination of HA, FA and humin were essentially identical to that of their HCl-treated original materials, except for a lower recovery of O-alkyl groups. Although the yield of HA extracted with PyroP was lower than that with NaOH, their spectral characteristics were not significantly different. The functionality of the OM, assuming a correlation with the sum of the proportions of carboxyl and phenolic groups, was higher in both HA and FA than that in humin. Based on the proportion and functionality of the HA in the OM, we conclude that the use of HA extracted with either NaOH or PyroP is valid for studies of OM functionality. The study also shows that the functionality and stability of OM are highly source dependent. We predict that amendments of the more humified turkey litter compost would have higher potential to increase SOM levels and retain nutrients compared to the source-separated organic compost and biosolid pellets.

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Ecosystem type effects on the stabilization of organic matter in soils: Combining size fractionation with sequential chemical extractions

Cited by 29 publications

References 60 publications

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Altered litter inputs modify carbon and nitrogen storage in soil organic matter in a lowland tropical forest

Validation and comparisons of NaOH and Na₄P₂O₇ extraction methods for the characterization of organic amendments

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Ecosystem type effects on the stabilization of organic matter in soils: Combining size fractionation with sequential chemical extractions

Cited by 29 publications

References 60 publications

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Tropical forest soil carbon stocks do not increase despite 15 years of doubled litter inputs

Altered litter inputs modify carbon and nitrogen storage in soil organic matter in a lowland tropical forest

Validation and comparisons of NaOH and Na4P2O7 extraction methods for the characterization of organic amendments

Contact Info

Product

Resources

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Validation and comparisons of NaOH and Na₄P₂O₇ extraction methods for the characterization of organic amendments