Carsten W. Mueller

University of Copenhagen · Department of Geosciences and Natural Resource Management

Litter-feeding soil animals are notoriously neglected in conceptual and mechanistic biogeo-chemical models. Yet, they may be a dominant factor in decomposition by converting large amounts of plant litter into faeces. Here, we assess how the chemical and physical changes occurring when litter is converted into faeces alter their fate during further...

Subsoils are characterized by low concentrations of organic carbon (OC); however, they contain more than half of the global soil OC because of their large volume. This discrepancy suggests that subsoils might further sequester carbon (C), thus acting as potential sinks for atmospheric C. Plant roots and associated rhizodeposits are a major OC input...

The interface between decaying plant residues and soil minerals represents an essential soil microenvironment at which soil organic matter forms. The high amount of microbial products and residues within this hot spot of microbial activity fosters the formation of mineral-associated organic matter. Besides classical quantitative analyses, our under...

The largest terrestrial organic carbon pool, carbon in soils, is regulated by an intricate connection between plant carbon inputs, microbial activity, and the soil matrix. This is manifested by how microorganisms, the key players in transforming plant-derived carbon into soil organic carbon, are controlled by the physical arrangement of organic and...

The connection between litter chemistry and the pathways controlling soil organic matter (SOM) formation and decay in forest ecosystems remains poorly understood, particularly in tropical soils. We addressed this question by incubating samples of a Ferralsol for 200 days with typical forest litter (leaves, twigs, bark, and roots) obtained from 13C-...

Much research focuses on increasing carbon storage in mineral-associated organic matter (MAOM), in which carbon may persist for centuries to millennia. However, MAOM-targeted management is insufficient because the formation pathways of persistent soil organic matter are diverse and vary with environmental conditions. Effective management must also...

Ice-rich Pleistocene-age permafrost is particularly vulnerable to rapid thaw, which may quickly expose a large pool of sedimentary organic matter (OM) to microbial degradation and lead to emissions of climate-sensitive greenhouse gases. Protective physico-chemical mechanisms may, however, restrict microbial accessibility and reduce OM decomposition...

One of the most prominent changes in the rhizospheric soil structure is associated with the formation of a strongly bound soil layer in the surroundings of the root, which is named rhizosheath. In this study, we investigated how root hair elongation, a ubiquitous root morphological trait, affect the stability of rhizosheath aggregates. Using 13CO2...

The molecular diversity of the source substrate has been regarded as a significant controller of the proportion of plant material that is either mineralized or incorporated into soil organic matter (SOM). However, quantitative parameters to express substrate molecular diversity remain elusive. In this research, we fractionated leaves, twigs, bark,...

Redox-driven biogeochemical cycling of iron plays an integral role in the complex process network of ecosystems, such as carbon cycling, the fate of nutrients and greenhouse gas emissions. We investigate Fe-(hydr)oxide (trans)formation pathways from rhyolitic tephra in acidic topsoils of South Patagonian Andosols to evaluate the ecological relevanc...

Examining in situ processes in the soil rhizosphere requires spatial information on physical and chemical properties under undisturbed conditions. We developed a correlative imaging workflow for targeted sampling of roots in their three-dimensional (3D) context and assessed the imprint of roots on chemical properties of the root-soil contact zone a...

Background and Aim Stomatal regulation allows plants to promptly respond to water stress. However, our understanding of the impact of above and belowground hydraulic traits on stomatal regulation remains incomplete. The objective of this study was to investigate how key plant hydraulic traits impact transpiration of maize during soil drying. We hyp...

Biological soil crusts (biocrusts) composed of cyanobacteria, bacteria, algae, fungi, lichens, and bryophytes stabilize the soil surface. This effect has mainly been studied in arid climates, where biocrusts constitute the main biological agent to stabilize and connect soil aggregates. Besides, biocrusts are an integral part of the soil surface und...

The spatial distribution of organic substrates and microscale soil heterogeneity significantly influence organic matter (OM) persistence as constraints on OM accessibility to microorganisms. However, it is unclear how changes in OM spatial heterogeneity driven by factors such as soil depth affect the relative importance of substrate spatial distrib...

Permafrost thaw will release additional carbon dioxide into the atmosphere resulting in a positive feedback to climate change. However, the mineralization dynamics of organic matter (OM) stored in permafrost-affected soils remain unclear. We used physical soil fractionation, radiocarbon measurements, incubation experiments, and a dynamic decomposit...

Soils of the super-humid southernmost Patagonian Andes between 49°S and 55°S, the core zone of the southern westerly wind belt (SWW), are still poorly studied. Such soil types include acidic Andosols (pH = 5 – 4) from the Magellanic moorlands (~53°S). They contain up to 20 wt.% total organic carbon and developed in volcanic ash deposits from the 4....

Increased human‐derived nitrogen (N) loading in terrestrial ecosystems has caused widespread ecosystem‐level phosphorus (P) limitation. In response, plants and soil micro‐organisms adopt a series of P‐acquisition strategies to offset N loading‐induced P limitation. Many of these strategies impose costs on carbon (C) allocation by plants and soil mi...

Redox-driven biogeochemical cycling of iron plays an integral role in the complex process network of terrestrial ecosystems, such as carbon and phosphorous cycling, the fate of nutrients and greenhouse gas emissions. We investigate Fe-(hydr)oxide (trans)formation pathways from volcanic glass and titanomagnetite phenocrysts in acidic topsoils of Sou...

For the prediction of permafrost nitrogen (N) climate feedbacks, a better process-based understanding of the N cycle in permafrost ecosystems is urgently needed. Therefore, we characterized and quantified soil organic matter, gross soil microbial ammonification and nitrification and soil-atmosphere exchange of nitrous oxide (N2O) of boreal permafro...

In permafrost soils, substantial amounts of organic carbon (OC) are potentially protected from microbial degradation and transformation into greenhouse gases by association with reactive iron (Fe) minerals. As permafrost environments respond to climate change, increased drainage of thaw lakes in permafrost regions is predicted. Soils will subsequen...

Soil carbon sequestration arises from the interplay of carbon input and stabilization, which vary in space and time. Assessing the resulting microscale carbon distribution in an intact pore space, however, has so far eluded methodological accessibility. Here, we explore the role of soil moisture regimes in shaping microscale carbon gradients by a n...

Reductive dissolution during permafrost thaw releases iron-bound organic carbon to pore-waters, rendering previously stable carbon vulnerable to microbial decomposition and subsequent release to the atmosphere. How mineral iron stability and the microbial processes influencing mineral dissolution vary during transitional permafrost thaw are poorly...

Biological soil crusts (biocrusts) composed of cyanobacteria, bacteria, algae, fungi, lichens, and bryophytes stabilize the soil surface. This effect has mainly been studied in arid climates, where biocrusts constitute the main biological agent to stabilize and connect soil aggregates. Besides, biocrusts are an integral part of the soil surface und...

Although the association of minerals and organic matter (OM) in soil plays an important role in the sequestration of C, the factors driving the initial formation of mineral-associated OM (MAOM), and thus the retention of new C input in soils are not yet fully understood. In this study, we investigated how the soil C loading and the differences in t...

Supply of phosphorus (P) as an agricultural input depends on a limited mineral rock phosphate reserve, but inefficient use means this resource is not being used sustainably. Moreover, losses of P from historically accumulated soil reserves can cause substantial environmental harm. Development of sustainable P management will require optimization of...

We still lack crucial knowledge about the contribution of plant vs. microbial residues to specific SOM pools, particularly the relative contribution of arbuscular (AM), ectomycorrhizal (ECM), and saprotrophic (SAP) fungi. We investigated sources of particulate and mineral organic matter (POM and MAOM) around trees with distinct mycorrhizal types, L...

Volcanic ash layers are important markers for the chronostratigraphy of paleoclimate and paleoenvironmental archives at the southern tip of South America. However, this requires that tephras are well-dated. We report geochemical data from stalagmite MA1 formed in a non-karst cave near Mt. Burney volcano in southernmost Patagonia (~53°S). High-resol...

Plain Language Summary The carbon cycle regulates Earth's climate by determining the amount of carbon in our atmosphere. Rivers are important for the carbon cycle because they deliver large amounts of organic carbon from mountains to the oceans. If this carbon is quickly buried in ocean sediment, atmospheric CO2 concentrations decrease. In order to...

The development of effective strategies to maintain/increase soil C is hindered by the poor process-level understanding of the impact of management practices on C preservation, particularly at different soil depths. Based on the distinct biogeochemistry existing across a soil profile, a depth-dependent response of organic matter (OM) to soil amendm...

Purpose Simultaneously interacting rhizosphere processes determine emergent plant behaviour, including growth, transpiration, nutrient uptake, soil carbon storage and transformation by microorganisms. However, these processes occur on multiple scales, challenging modelling of rhizosphere and plant behaviour. Current advances in modelling and experi...

The paradigm that permafrost-affected soils show restricted mineral nitrogen (N) cycling in favor of organic N compounds is based on the observation that net N mineralization rates in these cold climates are negligible. However, we find here that this perception is wrong. By synthesizing published data on N cycling in the plant-soil-microbe system...

Not only do soils provide 98.7% of the calories consumed by humans, they also provide numerous other functions upon which planetary survivability closely depends. However, our continuously increasing focus on soils for biomass provision (food, fiber, and energy) through intensive agriculture is rapidly degrading soils and diminishing their capacity...

Nano-scale secondary ion mass spectrometry (NanoSIMS) offers an unprecedented tool to complement classical quantitative measurements (e.g., isotopic ratio, elemental composition) by high resolution imaging of isotope and elemental distributions. It represents a unique technique to follow isotopically labelled compounds at soil microscale hot spots....

Correlations between organic carbon (OC) and fine mineral particles corroborate the important role of the abundance of soil minerals with reactive surfaces to bind and increase the persistence of organic matter (OM). The storage of OM broadly consists of particulate and mineral-associated forms. Correlative studies on the impact of fine mineral soi...

Soil organic carbon management is a nature-based carbon dioxide removal technology at the same time contributing to soil health and agricultural productivity. The soil science communities are refuting the traditional assumptions of the nature of soil organic matter (SOM) as based on ‘humic substances’ that are operationally-defined and have not bee...

In permafrost soils, substantial amounts of organic carbon (OC) are potentially protected from microbial degradation and transformation into greenhouse gases by association with reactive iron (Fe) minerals. As permafrost environments respond to climate change, increased drainage of thaw lakes in permafrost regions is predicted. Soils will subsequen...

As Antarctica is strongly affected by climate change and global warming, the factors that mainly determine soil development might also shift from the dominance of physical to biochemical processes. Vegetation is restricted to the margins of the Antarctic continent with the Antarctic Peninsula being a region of patchily distributed vegetation. While...

Reactive iron (Fe) minerals can preserve organic carbon (OC) in soils overlying intact permafrost. With permafrost thaw, reductive dissolution of iron minerals releases Fe and OC into the porewater, potentially increasing the bioavailability of OC for microbial decomposition. However, the stability of this so-called rusty carbon sink, the microbial...

Neutrophilic microbial pyrite (FeS 2) oxidation coupled to denitrification is thought to be an important natural nitrate attenuation pathway in nitrate-contaminated aquifers. However, the poor solubility of pyrite raises questions about its bioavailability and the mechanisms underlying its oxidation. Here, we investigated direct microbial pyrite ox...

Purpose Simultaneously interacting small-scale rhizosphere processes determine emergent plant-scale behaviour, including growth, transpiration, nutrient uptake, soil carbon storage and transformation by microorganisms. Current advances in modelling and experimental methods open the path to unravel and link those processes. Methods We present a seri...

Reactive iron (Fe) minerals can preserve organic carbon (OC) in soils overlying intact permafrost. With permafrost thaw, reductive dissolution of iron minerals releases Fe and OC into the porewater, potentially increasing the bioavailability of OC for microbial decomposition. However, the stability of this so-called rusty carbon sink, the microbial...

Geogenic organic carbon (GOC) from sedimentary rocks is an overlooked fraction in soils that has not yet been quantified but influences the composition, age, and stability of total organic carbon (OC) in soils. In this context, GOC is the OC in bedrock deposited during sedimentation. The contribution of GOC to total soil OC may vary, depending on t...

The development of high-resolution microscopy and spectroscopy techniques has allowed the analysis of microscopic 3D objects in fields like nanotechnology and life and soil sciences. Soils have the ability to incorporate and store large amounts of organic carbon. To study this organic matter (OM) sequestration, it is essential to analyze its associ...

Incomplete knowledge on the environmental factors linking litter decomposition and the formation of soil organic matter (SOM) hampers the sustainable management of soil as a carbon (C) sink. Here, we explored the effect of soil texture on the fate of C from decomposing litter (Indiangrass; Sorghastrum nutans (L.) Nash) and the concurrent formation...

Volcanic ash layers are important markers for the chronostratigraphy of paleoclimate and paleoenvironmental archives at the southern tip of South America. However, this requires that tephras are well-dated. We report geochemical data from the MA1 stalagmite formed in a non-karst cave near Mt. Burney volcano in southernmost Patagonia (~53°S). High-r...

Water-extractable organic carbon (WEOC) is considered as the most important carbon (C) source for denitrifying organisms, but the contribution of individual organic matter (OM) fractions (i.e., particulate (POM) and mineral-associated (MOM)) to its release and, thus, to denitrification remains unresolved. Here we tested short-time effects of POM an...

Clay minerals and pedogenic metal (oxyhydr)oxides are the most reactive soil mineral constituents controlling the long-term persistence of organic carbon (OC) in terrestrial ecosystems. However, their co-occurrence in most soils complicates direct assessment of their individual contribution to OC persistence. Making use of unique mineralogical comb...

The largest terrestrial organic carbon pool, carbon in soils, is regulated by the intricate connection between plant carbon inputs, microbial activity, and soil matrix. This is manifested by how microorganisms, the key players in transforming plant-derived carbon into soil organic carbon, are controlled by the physical arrangement of organic and in...

Climate and litter quality drive litter decomposition, but there is currently little consensus on their relative importance, likely because studies differ in the duration, the climatic gradients, and variability in litter‐trait values. Understanding these drivers is important because they determine the direct and indirect (via vegetation compositio...

Letter to the Editor of the European Journal of Soil Science as a reaction to the Russell Review by Phillipe Baveye “Bypass and hyperbole in soil research: worrisome practices critically reviewed through examples” and to his follow‐up Invited Opinion paper “Bypass and hyperbole in soil research: a personal view on plausible causes and possible reme...

It has been shown that reactive soil minerals, specifically iron(III) (oxyhydr)oxides, can trap organic carbon in soils overlying intact permafrost, and may limit carbon mobilization and degradation as it is observed in other environments. However, the use of iron(III)-bearing minerals as terminal electron acceptors in permafrost environments, and...

Tree roots penetrate the soil to several meters depth, but the role of subsoils for the supply of nutrient elements such as phosphorus (P) to the trees is poorly understood. Here, we tested the hypothesis that increased P deficiency in the topsoil results in an increased microbial recycling of P from the forest subsoil. We sampled soils from four G...

Grazed alpine pastures have shaped landscapes of the European Alps for millennia, but have partially been abandoned since the 1950s. Re-grazing of abandoned pastures could preserve this cultural landscape with its high species diversity, but also alter soil carbon and nitrogen cycles, as well as microbial communities, potentially affecting ecosyste...

Permafrost-affected soils of the Arctic account for 70 % or 727 Pg of the soil organic carbon (C) stored in the northern circumpolar permafrost region and therefore play a major role in the global C cycle. Most studies on the budgeting of C storage and the quality of soil organic matter (OM; SOM) in the northern circumpolar region focus on bulk soi...