Formation of mineral-associated organic matter in temperate soils is primarily controlled by mineral type and modified by land use and management intensity

Harnessing Microbes to Weather Native Silicates in Agricultural Soils for Scalable Carbon Dioxide Removal

Anthropogenic carbon emissions contribute significantly to the greenhouse effect, resulting in global warming and climate change. Thus, addressing this critical issue requires innovative and comprehensive solutions. Silicate weathering moderates atmospheric CO2 levels over geological time, but it occurs too slowly to counteract anthropogenic emissions effectively. Here, we show that the microorganism Bacillus subtilis strain MP1 promotes silicate weathering across different experimental setups with various levels of complexity. First, we found that MP1 was able to form a robust biofilm in the presence of feldspar and significantly increased (p < 0.05) silicate dissolution rates, pH, and calcium carbonate formation in culture experiments. Second, in mesocosm experiments, we found that MP1 enhanced the silicate weathering rate in soil by more than six times compared to the untreated control. In addition, soil inorganic carbon increased by 20%, and the concentrations of ions, including calcium, magnesium, and iron, were also elevated under the MP1 treatment. More importantly, when applied as a seed treatment on eight soybean fields, we found that MP1 significantly (p < 0.05) boosted soil inorganic carbon, leading to a gross accrual of 2.02 tonnes of inorganic carbon per hectare annually. Our findings highlight the potential of enhancing native silicate weathering with microorganisms in agricultural fields to increase soil inorganic carbon, contributing to climate change mitigation.

Ecological properties uniquely dictate molecular-level soil organic matter composition in a temperate forest in Central Europe with variation in litter deposition

Global climate change has increased temperatures and elevated atmospheric CO2 concentrations in many forests, which can impact plant productivity. This changes both the quantity and quality of litterfall and root inputs to soil organic matter (SOM) and alters soil carbon (C). This study examined how litter exclusions (No Litter, No Roots, and No Inputs) and additions (Double Litter and Double Wood) altered soil C dynamics and SOM composition. Soil samples were collected from a temperate forest in Hungary (the Síkfőkút Experimental Forest) after 20 years of experimental litter manipulation. Elemental analysis, targeted SOM compound techniques, nuclear magnetic resonance (NMR) spectroscopy and microbial biomass and community composition measurements were used to characterize alterations to SOM stabilization and destabilization processes. Our results contrast other similar long-term detrital manipulation experiments of the same timeframe, with increases in soil C for both Double Litter and Double Wood, and evidence for enhanced microbial decomposition still occurring. In North America, aboveground inputs are more influential for soil C stabilization in coniferous forests, while belowground inputs are more important in temperate forests. However, this temperate forest in Central Europe is unique in that the specific ecological properties (such as litter quality, mean annual temperature and precipitation) dictated these processes instead. This highlights the differing responses detrital manipulation to forest soils across varying climatic and edaphic gradients and the sensitivity of SOM composition to changes in detrital inputs in different ecosystems.

Potential influence mechanism of mineral-organic matter (OM) interactions on the mobility of toxic elements in Pb/Zn smelter contaminated soils

To date, how complex mineral-organic matter (OM) interactions affect the migration and mobility of potentially toxic elements (PTEs) in soils is highly understudied. This work mainly focused on the occurrence characteristics of PTEs and their close association with the composition characterization of mineral elements and dissolved OM (DOM) molecules. The results revealed that quartz (20.20%), albite (15.60%) and biotite (14.37%) were the dominant minerals in soils. CHO molecules were most abundant, accounting for 58.41%. The unsaturated hydrocarbons with both low and high O/C ratios were the dominant organic compounds, accounting for 21.56% and 36.73%, respectively. Sequential extraction results indicated that most Cd was hosted in carbonate minerals, while considerable amounts of As, Cu, Mn, Pb and Zn were bound to Fe/Mn oxyhydroxides. The elemental distribution characteristics displayed the coexistence of As, Cd, Cu, Mn, Pb and Zn with O, S, Al, Si, Ca and Fe. Fe oxyhydroxides might preferentially retain the unsaturated hydrocarbons with low O/C ratio and phenols. Furthermore, Fe oxide-organic composites had more significant impacts on Mn than As, Cd, Cu, Pb and Zn mobility. Overall, these findings would provide important insights into how mineral-OM interactions played the key roles on PTEs mobility in soils.

Foraging tunnel disturbances created by small subterranean herbivores enhance soil organic carbon stability but reduce carbon sequestration in different alpine grassland types

Foraging tunnel disturbances by small subterranean herbivores can alter soil properties and nutrient dynamics in grasslands, potentially altering soil organic carbon (SOC). Examining the impact of foraging tunnel disturbances on mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) is crucial for understanding SOC changes and its stability. However, the effects of these disturbances on POC and MAOC are not well documented. This study uses the plateau zokor (Eospalax baileyi) as a focal subterranean herbivore to investigate the effects of foraging tunnel disturbances on POC and MAOC in alpine steppes, alpine meadows, and alpine meadow steppes. Ninety paired quadrats were used for soil and plant sampling across three alpine grassland types. Results show that foraging tunnel disturbances consistently reduced POC concentrations across all grassland types, with reductions of 44.01 % in alpine steppes, 20.86 % in alpine meadows, and 29.58 % in alpine meadow steppes. MAOC concentrations decreased by 16.49 % in alpine steppes, while no significant changes in MAOC were observed in alpine meadows and alpine meadow steppes. The reduction in the POC to MAOC ratio indicates increased SOC stability. However, despite this increased stability, the change may lead to a decrease in overall carbon sequestration potential, as the total SOC in the soil declines. The main factors influencing POC and MAOC were soil moisture, belowground biomass, and microbial biomass carbon, with their influences varying by grassland type. The findings demonstrate that foraging tunnel disturbances by plateau zokors can lead to substantial modifications in SOC composition, influencing both its stability and sequestration potential. The disturbances necessitate tailored management strategies to mitigate their impacts, considering the unique characteristics of each grassland type to preserve carbon sequestration potential. This study contributes to a deeper understanding of the ecological role of small subterranean herbivores in the carbon cycle of alpine grassland ecosystems.

Divergent Changes in Soil Iron-Bound Organic Carbon Between Distinct Determination Methods

Fe-OC is crucial for SOC preservation in the global ecosystem. However, there is still significant uncertainty in the determination methods of Fe-OC, and these methods are often not calibrated to each other, making the Fe-OC content by different methods impossible to compare. Here, Fe-OC is analyzed by the CBD method and the SD method from 45 soils from different land types (e.g., wetland, grassland, and forest) to compare and analyze the uncertainty and influencing factors between the two methods. Our results showed that the Fe-OC contributions to SOC (fFe-OC) measured by CBD and SD methods were significantly lower in the wetland ecosystem than in grassland and forest ecosystems. The Fe-OC content and fFe-OC in the grassland ecosystem was significantly higher using the CBD method compared to the SD method, with no significant difference between the methods in wetland and forest ecosystems. The random forest model revealed that Fe-OCCBD content was mainly affected by C/N, Clay%, and TC, whereas SOC, total nitrogen, and soil inorganic carbon were the main influences on Fe-OCSD. Taken together, our findings highlight the importance of incorporating ecosystem types and soil properties into soil carbon estimation models when predicting and estimating Fe-OC and its contribution to SOC.

Towards an ecosystem capacity to stabilise organic carbon in soils

Soil organic carbon (SOC) accrual, and particularly the formation of fine fraction carbon (OCfine), has a large potential to act as sink for atmospheric CO2. For reliable estimates of this potential and efficient policy advice, the major limiting factors for OCfine accrual need to be understood. The upper boundary of the correlation between fine mineral particles (silt + clay) and OCfine is widely used to estimate the maximum mineralogical capacity of soils to store OCfine, suggesting that mineral surfaces get C saturated. Using a dataset covering the temperate zone and partly other climates on OCfine contents and a SOC turnover model, we provide two independent lines of evidence, that this empirical upper boundary does not indicate C saturation. Firstly, the C loading of the silt + clay fraction was found to strongly exceed previous saturation estimates in coarse-textured soils, which raises the question of why this is not observed in fine-textured soils. Secondly, a subsequent modelling exercise revealed, that for 74% of all investigated soils, local net primary production (NPP) would not be sufficient to reach a C loading of 80 g C kg-1 silt + clay, which was previously assumed to be a general C saturation point. The proportion of soils with potentially enough NPP to reach that point decreased strongly with increasing silt + clay content. High C loadings can thus hardly be reached in more fine-textured soils, even if all NPP would be available as C input. As a pragmatic approach, we introduced texture-dependent, empirical maximum C loadings of the fine fraction, that decreased from 160 g kg-1 in coarse to 75 g kg-1 in most fine-textured soils. We conclude that OCfine accrual in soils is mainly limited by C inputs and is strongly modulated by texture, mineralogy, climate and other site properties, which could be formulated as an ecosystem capacity to stabilise SOC.

Tannins and Climate Change: Are Tannins Able To Stabilize Carbon in the Soil?

The interaction between tannins and proteins has been studied intensively for more than half a century as a result of its significance for various applications. In chemical ecology, tannins are involved in response to environmental stress, including biotic (pathogens and herbivores) and abiotic (e.g., drought) stress, and in carbon (C) and nutrient cycling. This perspective summarizes the newest insights into the role of tannins in soil processes, including the interaction with fungi leading to C stabilization. Recent knowledge presented here may help to optimize land management to increase or preserve soil C to mitigate climate change.

Carbon Fate, Iron Dissolution, and Molecular Characterization of Dissolved Organic Matter in Thawed Yedoma Permafrost under Varying Redox Conditions

Permafrost soils store ∼50% of terrestrial C, with Yedoma permafrost containing ∼25% of the total C. Permafrost is undergoing degradation due to thawing, with potentially hazardous effects on landscape stability and water resources. Complicating ongoing efforts to project the ultimate fate of deep permafrost C is the poorly constrained role of the redox environment, Fe-minerals, and its redox-active phases, which may modulate organic C-abundance, composition, and reactivity through complexation and catalytic processes. We characterized C fate, Fe fractions, and dissolved organic matter (DOM) isolates from permafrost-thaw under varying redox conditions. Under anoxic incubation conditions, 33% of the initial C was lost as gaseous species within 21 days, while under oxic conditions, 58% of C was lost. Under anoxic incubation, 42% of the total initial C was preserved in a dissolved fraction. Lignin-like compounds dominated permafrost-thaw, followed by lipid- and protein-like compounds. However, under anoxic incubation conditions, there was accumulation of lipid-like compounds and reduction in the nominal oxidation state of C over time, regardless of the compound classes. DOM dynamics may be affected by microbial activity and abiotic processes mediated by Fe-minerals related to selective DOM fractionation and/or its oxidation. Chemodiversity DOM signatures could serve as valuable proxies to track redox conditions with permafrost-thaw.