Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

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Persistence of soil organic matter as an ecosystem property

Climate change 2014 - Synthesis Report

Summary
Mechanisms for C stabilization in soils have received much interest recently due to their relevance in the global C cycle. Here we review the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils: (i) selective preservation due to recalcitrance of OM, including plant litter, rhizodeposits, microbial products, humic polymers, and charred OM; (ii) spatial inaccessibility of OM against decomposer organisms due to occlusion, intercalation, hydrophobicity and encapsulation; and (iii) stabilization by interaction with mineral surfaces (Fe-, Al-, Mn-oxides, phyllosilicates) and metal ions. Our goal is to assess the relevance of these mechanisms to the formation of soil OM during different stages of decomposition and under different soil conditions. The view that OM stabilization is dominated by the selective preservation of recalcitrant organic components that accumulate in proportion to their chemical properties can no longer be accepted. In contrast, our analysis of mechanisms shows that: (i) the soil biotic community is able to disintegrate any OM of natural origin; (ii) molecular recalcitrance of OM is relative, rather than absolute; (iii) recalcitrance is only important during early decomposition and in active surface soils; while (iv) during late decomposition and in the subsoil, the relevance of spatial inaccessibility and organo-mineral interactions for SOM stabilization increases. We conclude that major difficulties in the understanding and prediction of SOM dynamics originate from the simultaneous operation of several mechanisms. We discuss knowledge gaps and promising directions of future research.

Stabilization of organic matter in temperate soils: mechanisms and their relevance under different soil conditions – a review

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.

The contentious nature of soil organic matter

SOURCE (OR PART OF THE FOLLOWING SOURCE): Type report Title Stikstofkringloop in kalkrijke en kalkarme duinbodems en de implicaties daarvan voor de effectiviteit van plaggen Author(s) A.M. Kooijman, J. Bloem, C. Cerli, G.A.J.M. Jagers op Akkerhuis, K. Kalbitz, K. Dimmers, A. Vos, A.K. Peest, R.H. Kemmers Faculty FNWI: Institute for Biodiversity and Ecosystem Dynamics (IBED), FNWI: Institute for Biodiversity and Ecosystem Dynamics (IBED), FNWI: Institute for Biodiversity and Ecosystem Dynamics (IBED) Year 2014

Stikstofkringloop in kalkrijke en kalkarme duinbodems

The Glacial – Terrestrial – Fluvial Pathway: A Multiparametrical Analysis of Spatiotemporal Dissolved Organic Matter Variation in Three Catchments of Lake Nam Co, Tibetan Plateau

Karsten Kalbitz

Papers

Stikstofkringloop in kalkrijke en kalkarme duinbodems

The Glacial – Terrestrial – Fluvial Pathway: A Multiparametrical Analysis of Spatiotemporal Dissolved Organic Matter Variation in Three Catchments of Lake Nam Co, Tibetan Plateau