As global change shifts the species composition of forests, we need to understand which species characteristics affect soil organic matter (SOM) cycling to predict future soil carbon (C) storage. ...Recently, whether a tree species forms a symbiosis with arbuscular (AM) versus ectomycorrhizal (EcM) fungi has been suggested as a strong predictor of soil C storage, but there is wide variability within EcM systems. In this study, we investigated how mycorrhizal associations and the species composition of canopy trees and mycorrhizal fungi related to the proportion of soil C and nitrogen (N) in mineral associations and soil C:N across four sites representing distinct climates and tree communities in the eastern US broadleaf forest biome. In two of our sites, we found the expected relationship of declining mineral‐associated C and N and increasing soil C:N ratios as the basal area of EcM‐associating trees increased. However, across all sites these soil properties strongly correlated with canopy tree and fungal species composition. Sites where the expected pattern with EcM basal area was observed were (1) dominated by trees with lower quality litter in the Pinaceae and Fagaceae families and (2) dominated by EcM fungi with medium‐distance exploration type hyphae, melanized tissues, and the potential to produce peroxidases. This observational study demonstrates that differences in SOM between AM and EcM systems are dependent on the taxa of trees and EcM fungi involved. Important information is lost when the rich mycorrhizal symbiosis is reduced to two categories.
Dissolved organic matter has been recognized as mobile, thus crucial to translocation of metals, pollutants but also of nutrients in soil. We present a conceptual model of the vertical movement of ...dissolved organic matter with soil water, which deviates from the view of a chromatographic stripping along the flow path. It assumes temporal immobilization (sorptive or by co-precipitation), followed by microbial processing, and re-release (by desorption or dissolution) into soil water of altered compounds. The proposed scheme explains well depth trends in age and composition of dissolved organic matter as well as of solid-phase organic matter in soil. It resolves the paradox of soil organic matter being oldest in the youngest part of the soil profile – the deep mineral subsoil.
► Improved conceptual model of DOM movement in soil. ► Physico-chemical immobilization by sorption and/or co-precipitation. ► Microbial processing of sorbed/co-precipitated matter, subsequent re-release (desorption/dissolution) of altered compounds. ► DOM mirrors soil organic matter. ► Model explains changes in soil organic matter properties with depth.
More than 10% of Australia's 49 M ha of grassland is considered degraded, prompting widespread interest in the management of these ecosystems to increase soil carbon (C) sequestration—with an ...emphasis on long‐lived C storage. We know that management practices that increase plant biomass also increase C inputs to the soil, but we lack a quantitative understanding of the fate of soil C inputs into different soil organic carbon (SOC) fractions that have fundamentally different formation pathways and persistence in the soil. Our understanding of the factors that constrain SOC formation in these fractions is also limited, particularly within tropical climates. We used isotopically labelled residue (13C) to determine the fate of residue C inputs into short‐lived particulate organic matter (POM) and more persistent mineral‐associated organic matter (MAOM) across a broad climatic gradient (ΔMAT 10°C) with varying soil properties. Climate was the primary driver of aboveground residue mass loss which corresponded to higher residue‐derived POM formation. In contrast, MAOM formation efficiency was constrained by soil properties. The differential controls on POM and MAOM formation highlight that a targeted approach to grassland restoration is required; we must identify priority regions for improved grazing management in soils that have a relatively high silt+clay content and cation exchange capacity, with a low C saturation in the silt+clay fraction to deliver long‐term SOC sequestration.
We know that management practices that increase plant biomass also increase C inputs to the soil, but we lack a quantitative understanding of the fate of soil C inputs into different soil organic carbon (SOC) fractions that have fundamentally different formation pathways and persistence in the soil. This study used isotopically labelled (13C residues) across a broad climatic gradient with varying soil properties to demonstrate that climate was the dominant driver of litter C mass loss and particulate organic matter formation (labile SOC), but mineral‐associated organic matter accumulation (stable SOC) was constrained by soil physical properties.
The extent to which long-term application of mineral fertilizers regulates the quantity, quality, and stability of soil organic matter (SOM) in soil matrices remains unclear. By combining four ...biomarkers, i.e., free and bound lipids, lignin phenols and amino sugars, we characterized the molecular composition, decomposition and origins of SOM in response to 10-year fertilization (400 kg N ha−1 yr−1, 120 kg P ha−1 yr−1 and 50 kg K ha−1 yr−1) in a cropland in North China. We focused on two contrasting fractions: particulate organic matter (POM), and mineral-associated organic matter (MAOM). Fertilization increased soil organic carbon (SOC) by 23% in MAOM, and altered its composition and origins, despite having a limited effect on bulk SOC levels. Fertilization increased plant-derived terpenoids by 46% in POM and long-chain lipids (≥C20) by 116% in MAOM but decreased short-chain lipids (<C20) by 54% in the former fraction. Fertilization reduced suberin-derived lipids by 56% in POM and 30% in MAOM but increased lignin-derived phenols by 74% in POM and 31% in MAOM, implying that crop residues were preferentially stored via the POM form. Fertilization decreased the contribution of microbial residues to SOC in both the fractions. Overall, mineral fertilizers tended to reduce certain labile components within POM (e.g., short-chain lipids), leading to the accrual of recalcitrant molecules (e.g., long-chain lipids, cutin-derived lipids, and lignin-derived phenols) in the MAOM fraction. Collectively, our study suggests that mineral fertilizers can increase SOM stability and persistence by modifying their molecular composition and preservation in the mineral-organic associations in a temperate agroecosystem.
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•Mineral fertilization altered molecular composition of SOM rather than its quantity.•Mineral fertilization increased SOC stored in the MAOM fraction.•Mineral fertilization decreased short-chain lipids in the POM fraction.•Mineral fertilization enriched resistant components in the MAOM fraction.•Mineral fertilization enhanced SOC persistence in croplands.
Chemodiversity in freshwater health Tanentzap, Andrew J; Fonvielle, Jérémy A
Science (American Association for the Advancement of Science),
2024-Mar-29, Letnik:
383, Številka:
6690
Journal Article
Recenzirano
Dissolved organic matter may offer a way to track and restore the health of fresh waters.
Soil organic matter (SOM) is correlated with reactive iron (Fe) in humid soils, but Fe also promotes SOM decomposition when oxygen (O
) becomes limited. Here we quantify Fe-mediated OM protection vs. ...decomposition by adding
C dissolved organic matter (DOM) and
Fe
to soil slurries incubated under static or fluctuating O
. We find Fe uniformly protects OM only under static oxic conditions, and only when Fe and DOM are added together: de novo reactive Fe
phases suppress DOM and SOM mineralization by 35 and 47%, respectively. Conversely, adding
Fe
alone increases SOM mineralization by 8% following oxidation to
Fe
. Under O
limitation, de novo reactive
Fe
phases are preferentially reduced, increasing anaerobic mineralization of DOM and SOM by 74% and 32‒41%, respectively. Periodic O
limitation is common in humid soils, so Fe does not intrinsically protect OM; rather reactive Fe phases require their own physiochemical protection to contribute to OM persistence.
•Molecular properties of DOM from the Three Gorges Reservoir water fluctuation zone•Phenolic, aliphatic and microbial-derived structures are the main constituents.•Soil DOM of TGR area is a mixture ...of “allochthonous” and “autochthonous” origins.•Microbial terrigenous DOM contributes to apparent “autochthonous” fingerprint.•Multi-methodological approach essential for unambiguous DOM characterization
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Soil-derived dissolved organic matter (DOM) has a major influence in biogeochemical processes related to contaminant dynamics and greenhouse gas emissions, due to its reactivity and its bridging role between the soil and aquatic systems. Within the Three Gorges Reservoir (TGR, China) area, an extensive water-fluctuation zone periodically submerges the surrounding soils. Here we report a characterization study of soil-derived DOM across the TGR areas, using elemental and optical analysis, infrared spectroscopy (FTIR), pyrolysis-GC–MS (Py-GC–MS) and thermally assisted hydrolysis and methylation (THM-GC–MS). The results showed that the soil DOM from the TGR area is a mixture of “allochthonous” (i.e., plant-derived/terrigenous) and “autochthonous” (i.e., microbial) origins. The terrigenous DOM is composed primarily of phenolic and aliphatic structures from lignin and aliphatic biopolymers (i.e. cutin, suberin), respectively. Multivariate statistics differentiated between two fractions of the microbial DOM, i.e. chitin-derived, perhaps from fungi and arthropods in soil, and protein-derived, partially sourced from algal or aquatic organisms. Molecular proxies of source and degradation state were in good agreement with optical parameters such as SUVA254, the fluorescence index (FI) and the humification index (HIX). The combined use of elemental analysis, fluorescence spectroscopy, and Py-GC–MS provides rigorous and detailed DOM characterization, whereas THM-GC–MS is useful for more precise but qualitative identification of the different phenolic (cinnamyl, p-hydroxyphenyl, guaiacyl, syringyl and tannin-derived) and aliphatic materials. With the multi-methodological approach used in this study, FTIR was the least informative, in part, because of the interference of inorganic matter in the soil DOM samples. The soil DOM from the TGR's water fluctuation zone exhibited considerable compositional diversity, mainly related to the balance between DOM source (microbial- or plant-derived), local vegetation and anthropogenic activities (e.g., agriculture). Finally, the relationship between DOM composition and its potential reactivity with substances of environmental concerns in the TGR area are also discussed.
Soil organic matter (SOM) is an important natural resource. It is fundamental to soil and ecosystem functions across a wide range of scales, from site-specific soil fertility and water holding ...capacity to global biogeochemical cycling. It is also a highly complex material that is sensitive to direct and indirect human impacts. In SOM research, simulation models play an important role by providing a mathematical framework to integrate, examine, and test the understanding of SOM dynamics. Simulation models of SOM are also increasingly used in more 'applied' settings to evaluate human impacts on ecosystem function, and to manage SOM for greenhouse gas mitigation, improved soil health, and sustainable use as a natural resource. Within this context, there is a need to maintain a robust connection between scientific developments in SOM modeling approaches and SOM model applications. This need forms the basis of this review. In this review we first provide an overview of SOM modeling, focusing on SOM theory, data-model integration, and model development as evidenced by a quantitative review of SOM literature. Second, we present the landscape of SOM model applications, focusing on examples in climate change policy. We conclude by discussing five areas of recent developments in SOM modeling including: (1) microbial roles in SOM stabilization; (2) modeling SOM saturation kinetics; (3) temperature controls on decomposition; (4) SOM dynamics in deep soil layers; and (5) SOM representation in earth system models. Our aim is to comprehensively connect SOM model development to its applications, revealing knowledge gaps in need of focused interdisciplinary attention and exposing pitfalls that, if avoided, can lead to best use of SOM models to support policy initiatives and sustainable land management solutions.
The pervasive presence of plastic waste in the aquatic environment is widely viewed as one of the most serious environmental challenges for current and future generations. Microplastics ultimately ...degrade into nano and smaller-sizes. In turn, their biological and ecological impacts become more complicated and ambiguous. Nano-plastic particles travel from freshwater systems to estuarine and oceanic regions, during which they can interact with dissolved organic matter (DOM) to form microgels. Microgel formation is ubiquitous in aquatic systems, serving as a shunt between DOM and particulate organic matter (POM), as well as playing key roles in particle aggregation/sedimentation and pollutant transport. Currently the influences and mechanisms of the aggregation behavior and environmental fate of nano-plastics in different aquatic environments is poorly understood. Here, we report that 25 nm polystyrene nano-particles in lake and river water can promote POM (microgel) formation and accelerate the DOM–POM transition. We also adjusted various salinities of water samples to simulate scenarios based on plastic transport in waters flowing from rivers to seas. The results indicate polystyrene nanoparticles can interact with organic matter to form large organic particles, which may undergo further settling in response to specific salinity levels. Polystyrene-induced microgel formation appears to involve the hydrophobic interactions between plastics and DOM. Our data provides much needed information for modeling and understanding the retention and sedimentation of nano-plastics. We show that nano-plastics alter the DOM–POM shunt to cause unanticipated perturbations in the functionality of aquatic ecosystems.
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•Nano-plastics can interact with dissolved organic matter (DOM) to form microgels.•Nano-plastics can increase the microgel abundance at specific salinities•The facilitation of microgel formation involves DOM–plastics crosslinking via hydrophobic interactions.
The extent to which ectomycorrhizal (ECM) fungi enable plants to access organic nitrogen (N) bound in soil organic matter (SOM) and transfer this growth-limiting nutrient to their plant host, has ...important implications for our understanding of plant–fungal interactions, and the cycling and storage of carbon (C) and N in terrestrial ecosystems. Empirical evidence currently supports a range of perspectives, suggesting that ECM vary in their ability to provide their host with N bound in SOM, and that this capacity can both positively and negatively influence soil C storage. To help resolve the multiplicity of observations, we gathered a group of researchers to explore the role of ECM fungi in soil C dynamics, and propose new directions that hold promise to resolve competing hypotheses and contrasting observations. In this Viewpoint, we summarize these deliberations and identify areas of inquiry that hold promise for increasing our understanding of these fundamental and widespread plant symbionts and their role in ecosystem-level biogeochemistry.
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