The contentious nature of soil organic matter
TL;DR: It is argued that the available evidence does not support the formation of large-molecular-size and persistent ‘humic substances’ in soils, and instead soil organic matter is a continuum of progressively decomposing organic compounds.
Abstract: Instead of containing stable and chemically unique ‘humic substances’, as has been widely accepted, soil organic matter is a mixture of progressively decomposing organic compounds; this has broad implications for soil science and its applications. The exchange of nutrients, energy and carbon between soil organic matter, the soil environment, aquatic systems and the atmosphere is important for agricultural productivity, water quality and climate. Long-standing theory suggests that soil organic matter is composed of inherently stable and chemically unique compounds. Here we argue that the available evidence does not support the formation of large-molecular-size and persistent ‘humic substances’ in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds. We discuss implications of this view of the nature of soil organic matter for aquatic health, soil carbon–climate interactions and land management. Soil organic matter contains a large portion of the world's carbon and plays an important role in maintaining productive soils and water quality. Nevertheless, a consensus on the nature of soil organic matter is lacking. Johannes Lehmann and Markus Kleber argue that soil organic matter should no longer be seen as large and persistent, chemically unique substances, but as a continuum of progressively decomposing organic compounds.
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TL;DR: This Perspective looks at how microbial anabolism and the soil microbial carbon pump control microbial necromass accumulation and stabilization; the ‘entombing effect’.
Abstract: This Perspective looks at how microbial anabolism and the soil microbial carbon pump control microbial necromass accumulation and stabilization; the ‘entombing effect’.
1,042 citations
TL;DR: This work provides the first direct evidence that soil microbes produce chemically diverse, stable SOM, and shows that SOM accumulation is driven by distinct microbial communities more so than clay mineralogy, where microbial-derived Som accumulation is greatest in soils with higher fungal abundances and more efficient microbial biomass production.
Abstract: Soil organic matter (SOM) and the carbon and nutrients therein drive fundamental submicron- to global-scale biogeochemical processes and influence carbon-climate feedbacks. Consensus is emerging that microbial materials are an important constituent of stable SOM, and new conceptual and quantitative SOM models are rapidly incorporating this view. However, direct evidence demonstrating that microbial residues account for the chemistry, stability and abundance of SOM is still lacking. Further, emerging models emphasize the stabilization of microbial-derived SOM by abiotic mechanisms, while the effects of microbial physiology on microbial residue production remain unclear. Here we provide the first direct evidence that soil microbes produce chemically diverse, stable SOM. We show that SOM accumulation is driven by distinct microbial communities more so than clay mineralogy, where microbial-derived SOM accumulation is greatest in soils with higher fungal abundances and more efficient microbial biomass production. Soil microbes process plant remnants and are hypothesized to synthesize soil organic matter (SOM). Here, Kallenbach and colleagues directly measure chemically diverse and stable SOM derived from microbial communities in the absence of plant compounds.
853 citations
TL;DR: Current knowledge on available methods for the quantification and identification of plastic in soil, the quantity and possible input pathways of plastic into soil, and its fate in soil are reviewed are reviewed to ensure the applicability of these methods for soil needs to be tested.
842 citations
TL;DR: Plant growth promoting rhizobacteria (PGPR) has been functioning as a co-evolution between plants and microbes showing antagonistic and synergistic interactions with microorganisms and the soil.
648 citations
TL;DR: Conceptualizing SOM into POM versus MAOM is a feasible, well-supported, and useful framework that will allow scientists to move beyond studies of bulk SOM, but also use a consistent separation scheme across studies.
Abstract: Managing soil organic matter (SOM) stocks to address global change challenges requires well-substantiated knowledge of SOM behavior that can be clearly communicated between scientists, management practitioners, and policy makers. However, SOM is incredibly complex and requires separation into multiple components with contrasting behavior in order to study and predict its dynamics. Numerous diverse SOM separation schemes are currently used, making cross-study comparisons difficult and hindering broad-scale generalizations. Here, we recommend separating SOM into particulate (POM) and mineral-associated (MAOM) forms, two SOM components that are fundamentally different in terms of their formation, persistence, and functioning. We provide evidence of their highly contrasting physical and chemical properties, mean residence times in soil, and responses to land use change, plant litter inputs, warming, CO2 enrichment, and N fertilization. Conceptualizing SOM into POM versus MAOM is a feasible, well-supported, and useful framework that will allow scientists to move beyond studies of bulk SOM, but also use a consistent separation scheme across studies. Ultimately, we propose the POM versus MAOM framework as the best way forward to understand and predict broad-scale SOM dynamics in the context of global change challenges and provide necessary recommendations to managers and policy makers.
521 citations
Cites background from "The contentious nature of soil orga..."
...…by‐products of extraction and inaccurate proxies for naturally occurring SOM began to emerge as early as the 1840s (see references to Mulder and Eggertz in Baveye & Wander, 2019; Waksman, 1936), and they have more recently been dismissed by much of the SOM community (Lehmann & Kleber, 2015)....
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...MAOM can form in multiple ways, but the main pathways pertain to the min‐ eral adsorption of relatively low molecular weight compounds (Lehmann & Kleber, 2015), which are thought to be the main component of the most persistent portion of MAOM....
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References
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Book•
01 Jan 1962
TL;DR: The Structure of Scientific Revolutions as discussed by the authors is a seminal work in the history of science and philosophy of science, and it has been widely cited as a major source of inspiration for the present generation of scientists.
Abstract: A good book may have the power to change the way we see the world, but a great book actually becomes part of our daily consciousness, pervading our thinking to the point that we take it for granted, and we forget how provocative and challenging its ideas once were-and still are. "The Structure of Scientific Revolutions" is that kind of book. When it was first published in 1962, it was a landmark event in the history and philosophy of science. And fifty years later, it still has many lessons to teach. With "The Structure of Scientific Revolutions", Kuhn challenged long-standing linear notions of scientific progress, arguing that transformative ideas don't arise from the day-to-day, gradual process of experimentation and data accumulation, but that revolutions in science, those breakthrough moments that disrupt accepted thinking and offer unanticipated ideas, occur outside of "normal science," as he called it. Though Kuhn was writing when physics ruled the sciences, his ideas on how scientific revolutions bring order to the anomalies that amass over time in research experiments are still instructive in our biotech age. This new edition of Kuhn's essential work in the history of science includes an insightful introductory essay by Ian Hacking that clarifies terms popularized by Kuhn, including paradigm and incommensurability, and applies Kuhn's ideas to the science of today. Usefully keyed to the separate sections of the book, Hacking's essay provides important background information as well as a contemporary context. Newly designed, with an expanded index, this edition will be eagerly welcomed by the next generation of readers seeking to understand the history of our perspectives on science.
36,808 citations
34,393 citations
01 Jan 2007
TL;DR: The first volume of the IPCC's Fourth Assessment Report as mentioned in this paper was published in 2007 and covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
Abstract: This report is the first volume of the IPCC's Fourth Assessment Report. It covers several topics including the extensive range of observations now available for the atmosphere and surface, changes in sea level, assesses the paleoclimatic perspective, climate change causes both natural and anthropogenic, and climate models for projections of global climate.
32,826 citations
TL;DR: In this article, the carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon.
Abstract: :The carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.
5,835 citations
"The contentious nature of soil orga..." refers background in this paper
...(2) ‘Selective preservation’, which is also called preferential decomposition25, is a newer concept informed by decomposition studies of leaves26,27 and visible plant fragments in soils28....
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...(2) The harsh alkaline treatment at pH 13 ionizes...
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...Reconciling models of soil organic matter At present, three competing models for the fate of organic inputs to soil can be distinguished: (1) classic ‘humification’, (2) ‘selective preservation’ and (3) ‘progressive decomposition’ (Fig....
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Book•
01 Jan 1982
TL;DR: In this paper, the authors present an analysis of organic matter in soil using NMR Spectroscopy and analytical pyrolysis, showing that organic matter is composed of nitrogen and ammonium.
Abstract: Partial table of contents: Organic Matter in Soils: Pools, Distribution, Transformations, and Function. Extraction, Fractionation, and General Chemical Composition of Soil Organic Matter. Organic Forms of Soil Nitrogen. Native Fixed Ammonium and Chemical Reactions of Organic Matter with Ammonia and Nitrite. Organic Phosphorus and Sulfur Compounds. Soil Carbohydrates. Soil Lipids. Biochemistry of the Formation of Humic Substances. Reactive Functional Groups. Structural Components of Humic and Fulvic Acids as Revealed by Degradation Methods. Characterization of Soil Organic Matter by NMR Spectroscopy and Analytical Pyrolysis. Structural Basis of Humic Substances. Spectroscopic Approaches. Colloidal Properties of Humic Substances. Electrochemical and Ion-Exchange Properties of Humic Substances. Organic Matter Reactions Involving Pesticides in Soil. Index.
5,658 citations