Decomposition Of Organic Matter Research Articles

Long‐Term Effects of Arable and Tree Cropping Systems on Soil Organic Carbon and Nitrogen Dynamics in a Tropical Agroecological Transition Zone

ABSTRACTContinuous cropping can affect soil carbon and nitrogen stocks and litter decomposition, but research on smallholder farms in Africa is limited. This study, conducted from 2020 to 2023 in Ghana's forest‐savanna transition zone, examined four cropping systems: continuous maize monocrop (M), maize rotated with legumes (ML), young cashew intercropped with maize or legumes (YCM/L), and mature cashew (MC). The objective was to assess the long‐term impact of the cropping systems on soil organic carbon (SOC), nitrogen (N) stocks, and soil organic matter (SOM) decomposition rates using the tea bag protocol. Results showed significant variability in SOC and N stocks across the systems. At a 0–15 cm depth, SOC in the MC and M systems was 160% and 149% higher than in the YCM/L system. At 15–30 cm, SOC in the M and MC systems was 86% and 132% higher than in YCM/L. Soil nitrogen stocks followed a similar trend, with MC and M systems showing 94%–199% higher values than YCM/L at both depths. SOM decomposition rates for green and rooibos tea in the MC and ML systems were statistically similar after 90 days of incubation (p > 0.05). This study, the first to use the tea bag protocol in Ghanaian soils, revealed that mature cashew and sustainable practices, such as adding maize stover, can enhance SOC and N stocks in highly weathered tropical soils. These findings underscore the potential for specific cropping systems to improve soil health on smallholder farms.

Deciphering the active bacteria involving glucose-triggered priming effect in soils with gradient N inputs

The soil priming effect, which refers to the alteration of soil organic matter (SOM) decomposition due to labile carbon (C) inputs, is widely acknowledged for its impact on C storage in terrestrial ecosystems. However, the impact of chronic nitrogen (N) fertilizer on soil priming effect, particularly in agroecological systems, remains unclear. Here, we utilized soils subjected to varying levels of N fertilization (0, 140, 280, 470, and 660 kg N ha−1 y−1), which were collected from a long-term experimental site. Enzyme activity related to C, N, and phosphorus (P) acquisition was measured using the fluorometric method. Additionally, DNA-based stable isotope probing with 13C-labeled glucose was conducted to explore the role of active bacterial communities (16S rRNA gene analysis) on the priming effect in soils with different N fertilization histories. Glucose addition enhanced the decomposition of native SOM and induced positive priming effects in all soils, which were amplified by the historical N application level. Activity of C-related enzymes essential for soil C decomposition increased following glucose addition, which was positively correlated with the soil priming effect. Active bacterial taxa, primarily Firmicutes, Actinobacteria, and Proteobacteria, were capable of assimilating exogenous glucose-C or native SOM-C. Notably, bacteria assimilating glucose exhibited higher abundance-weighted average ribosomal RNA gene operon copy number than those assimilating SOM, indicating the role of r-strategists in accelerating SOC turnover and increasing C loss. These findings highlight the role of active microbial community attributes on the soil priming effects. This study provides new insights into the intricate processes of C transformation in soils subjected to long-term N management in agroecosystems.

Study on Grain Size, Physical Properties and Organic Matter Characteristics of Tidal Flat Surface Sediments: May 2022 Hwangdo Tidal Flat Dataset, Cheonsu Bay

This study analyzes the geological and geochemical features of surface sediments in the Hwangdo Tidal Flat, located on Korea’s West Coast. The tidal flat experiences semi-diurnal tides, impacting organic matter decomposition and nutrient cycling. Ninety one sediment samples were collected and analyzed for physical and chemical properties including grain size, density, water content, organic carbon, and nitrogen. Sediments consist mainly of sand and silt, with coarser sediments near the main channel and finer sediments towards the west. Sediment grain size averages 4.12 Φ with a sorting coefficient of 1.96 Φ, indicating diverse energy environments. Total organic carbon and nitrogen correlate positively with grain size and density, reflecting sediment origin and environment. Kriging maps sediment grain size distribution, while correlation and linear regression analyses show relationships between variables. High correlations exist between various parameters, aligning with tidal flat characteristics and aiding understanding of sediment transport and deposition. The study provides baseline data for understanding the tidal flat’s geological, geochemical, and physical aspects, valuable for remote sensing validation and environmental monitoring. The dataset is freely available for research and management purposes.

Examining the adaptability of soil pH to soil dynamics using different methodologies: A concise review

Soil pH is crucial to soil health, influencing nutrient availability, microbial activity, and plant growth. This review aims to assess the adaptability of soil pH under changing soil conditions by analyzing natural and human factors. Information was gathered from various sources, including peer-reviewed articles, field studies, and recent advances in soil science. The study explores how natural factors such as parent material, climate, and vegetation establish baseline soil pH, while human activities such as intensive farming and land-use changes further modify it, often leading to soil acidification or alkalinization. Traditional management methods like lime application, organic amendments, and crop rotation are reviewed for their effectiveness in stabilizing soil pH and their limitations under varying soil conditions. The review also explores modern technological innovations like precision agriculture, which uses soil sensors and variable rate technology for targeted pH management, and biological approaches, such as microbial inoculants, to enhance nutrient cycling and organic matter decomposition. Integrating these traditional and contemporary approaches is essential for sustainable soil pH management and long-term productivity. The findings highlight the need for a holistic approach that combines historical knowledge with emerging technologies to promote sustainable agricultural practices and environmental conservation.

Brownfield Topsoil Vertical Heterogeneity: Implications for Germination and Soil Microbial Functioning.

Soil vertical heterogeneity refers to the variation in soil properties and composition with depth. In uncontaminated soils, properties including the organic matter content and nutrient concentrations typically change gradually with depth due to natural processes such as weathering, leaching, and organic matter decomposition. In contaminated soils, heavy metals and organic contaminants can migrate vertically through leaching or root uptake and translocation by plants and macrobiota, if present, leading to vertical heterogeneity in contaminant concentrations at different depths. Contaminants can alter soil properties, and we investigated the implications of soil vertical heterogeneity for germination and microbial functioning. We collected soil from an urban brownfield and created two conditions: structured soil samples collected with the soil core intact and mixed (unstructured) samples. When planted, the germination rate was significantly lower in the structured conditions (3.1 ± 1.7%) compared to mixed soils (17 ± 4.6%), suggesting that the vertical heterogeneity of contaminated soil influenced plant germination. To map the vertical distribution of contaminants and nutrient cycling rates in the structured soil samples, we collected 10 cm-deep soil cores from the barren site and a neighboring vegetated reference site and measured heavy metal concentrations, soil enzyme activities, and organic matter content in five 2 cm vertical layers. In the barren soil cores, metals were found concentrated in the top 2 cm layer, while in the vegetated soil cores, metals were uniformly distributed. No significant differences were observed for the organic matter content or moisture along depth. Published studies on vertical distribution of enzyme activities and metal concentrations have treated the top 10-20 cm as a single layer and thus would have not revealed the thin (<2 cm thick) metal cap on the surface of the barren soil core. Despite the metal cap, enzyme activities in the top layer were similar to those in the lower layers of the barren soil core, suggesting that high metal concentrations do not limit soil enzyme activity under all circumstances. Investigating vertical heterogeneity in postindustrial soils can inform efforts to convert industrial barrens to vegetated environments.

Soil Organic Carbon Dynamics: Drivers of Climate Change-induced Soil Organic Carbon Loss at Various Ecosystems

At roughly 2500 Peta gram (Pg) C, soil organic carbon (SOC) is the biggest carbon store in terrestrial ecosystems and is a crucial contributor to vital soil functions and ecosystem services, such as agricultural soil productivity. SOC stocks are in a dynamic equilibrium between C inputs, primarily from crop residues and organic manures, and C loss owing to decomposition and mineralization of soil organic matter (SOM) under long-term constant land management and environmental circumstances. In addition, the rate of C addition in native ecosystems is governed by the nature and productivity of the local flora, which is mostly influenced by climatic conditions. However, being a complex system, various factors, such as soil management and land-use change influence the soil C pool. Along with temperature gradients from temperate to tropical regions, SOC supplies were shown to be shrinking on a global and regional basis. This reflects the rates of SOM decomposition as a function of temperature, which fluctuates more rapidly than net primary production (NPP). SOM decomposition rates are also influenced by several parameters, including soil temperature and moisture, soil respiration and pH, and soil physical properties including texture and clay mineralogy. Nonetheless, increased temperatures as a result of climate change are thought to be the primary driver of accelerated decomposition, which results in considerable reductions in SOC supplies and sequestration. Furthermore, climatic change contributes to soil deterioration by increasing the mineralization of the SOC pool and causing desertification (irreversible expansion of desert landforms). Similarly, erosion is a degrading process that affects C dynamics and leads to terrestrial carbon loss through the breakdown of structural aggregates, as well as lower productivity in eroding areas due to a lack of soil nutrients. Thus, for an in-depth understanding of worldwide soil C dynamics and to provide support to C management and decision support systems to policymakers and land managers in the face of changing climates, comprehensive research on the influence of multiple climate-induced drivers on soil C is required.

Carbon sequestration through conservation tillage in sandy soils of arid and semi-arid climates: A meta-analysis

This meta-analysis assessed soil organic carbon (SOC) percent changes in sandy soils, transitioning from conventional tillage (CT) to conservational tillage (CST) in arid and semi-arid climates. High levels of SOC in sandy soils are difficult to attain especially when precipitation levels are very low, contributing to low biomass production, and increased decomposition of organic matter. While CT practices are known to reduce SOC through the breakdown of soil aggregates, accelerated decomposition of soil organic matter, and promote erosion, CST methods (i.e., mulch tillage, no tillage, reduced tillage, ridge tillage, etc.) offer the potential to preserve soil aggregates and increase SOC concentration. Analyzing 55 peer-reviewed publications in arid and semi-arid climates with ≥ 45 % sand content, this study compared SOC content between CST and CT over short- and long-term periods (349 paired observations). Results showed that CST increased SOC in sandy soils, with an estimated 12.74 ± 1.46 % increase. Specifically, reduced tillage (RdT), mulch tillage (MchT), and no tillage (NT) exhibited the highest increases of SOC by 18.94 ± 2.48 %, 11.45 ± 2.46 %, and 10.06 ± 2.46 %, respectively, compared to CT. Studies with durations of up to 15 years (n = 297) showed a progressive increase in SOC concentrations under CST; however, the long-term stability of the accrued carbon content in sandy soils of arid and semi-arid climates is still uncertain, as studies extending beyond 15 years (n = 52) did not demonstrate significant changes in SOC levels. CST significantly raised SOC concentrations in precipitation up to 600 mm, though no significant changes were observed for precipitation over 600 mm. In soils with over 56 % sand content, CST increased SOC by approximately 13 %. This study highlights both positive and limited impacts of CST practices for soil conservation and climate change mitigation, emphasizing their significance for both existing agricultural areas in arid regions and those in parts of the world where aridity is on the rise.

Phytobiomes: Harnessing the Power of Microbial Communities for Plant Health

Phytobiomes encompass the dynamic ecosystems surrounding plants, which include a diverse range of microbial communities such as fungi, bacteria, algae, viruses, and nematodes. These microorganisms interact intricately with plants, influencing their health, growth, and resilience. Beneficial fungi form symbiotic relationships with plant roots, enhancing nutrient absorption, while bacteria play a role in nitrogen fixation and disease suppression. Algae contribute to soil health and organic matter decomposition, and viruses, though often seen as harmful, can provide resistance to certain pathogens. Nematodes, both beneficial and parasitic, regulate soil nutrient cycles and influence plant growth. Harnessing the potential of these microbial communities offers promising solutions for sustainable agriculture. By promoting beneficial interactions within the phytobiome, it is possible to improve plant productivity, enhance nutrient use efficiency, and increase tolerance to environmental stresses such as drought, salinity, and pathogens. Phytobiome research aims to uncover the complex relationships within these microbial networks to develop novel agricultural practices that reduce reliance on chemical inputs. This holistic approach not only promotes plant health but also ensures ecological balance, contributing to the long-term sustainability of agroecosystems in the face of environmental challenges. Understanding the power of microbial communities within phytobiomes is key to advancing future agricultural innovations.

Mechanisms of soil organic carbon and nitrogen stabilization in mineral-associated organic matter – insights from modeling in phase space

Abstract. Understanding the mechanisms of plant-derived carbon (C) and nitrogen (N) transformation and stabilization in soil is fundamental for predicting soil capacity to mitigate climate change and support other soil functions. The decomposition of plant residues and particulate organic matter (POM) contributes to the formation of mineral-associated (on average more stable) organic matter (MAOM) in soil. MAOM is formed from the binding of dissolved organic matter (ex vivo pathway) or microbial necromass and bioproducts (in vivo pathway) to minerals and metal colloids. Which of these two soil organic matter (SOM) stabilization pathways is more important and under which conditions remains an open question. To address this question, we propose a novel diagnostic model to describe C and N dynamics in MAOM as a function of the dynamics of residues and POM decomposition. Focusing on relations among soil compartments (i.e., modeling in phase space) rather than time trajectories allows isolating the fundamental processes underlying stabilization. Using this diagnostic model in combination with a database of 36 studies in which residue C and N were tracked into POM and MAOM, we found that MAOM is predominantly fueled by necromass produced by microbes decomposing residues and POM. The relevance of this in vivo pathway is higher in clayey soils but lower in C-rich soils and with N-poor added residues. Overall, our novel modeling in phase space proved to be a sound diagnostic tool for the mechanistic investigation of soil C dynamics and supported the current understanding of the critical role of both microbial transformation and mineral capacity for the stabilization of C in mineral soils.

Seaweed burial mitigated the release of organic carbon and nutrients by regulating microbial activity

Seaweed debris is susceptible to being buried in sediments due to natural environmental changes and human activities. So far, the effect of buried seaweeds on the environment and its decomposition mechanism remains unclear. This study simulated the decomposition of seaweed Gracilariopsis lemaneiformis for 180 days with different burial depths (0 cm and 10 cm) and burial weights (10 g and 20 g). Our findings revealed that compared with Gracilariopsis decomposition on the sediment surface, the seaweed buried in sediment slowed down the release of N, P, and dissolved organic carbon (DOC) by enhancing the activity of diverse anaerobic microbes (i.e. Draconibacterium, Desulfuromusa, Sediminispirochaeta), which were associated with organic matter decomposition. The enhanced burial quantity of Gracilariopsis resulted in a 3.28 % increase in sediment OC and enriched the humification degree of DOC in seawater. These results highlight the role of seaweed burial in enhancing OC sequestration in marine environments.

Influences and mechanisms of iron input for methane productions in peatlands.

Atmospheric deposition provides a stable iron source for peatlands. The influences of Fe input on methane (CH4) productions and the underlying mechanisms remain unclear. We conducted a microcosm experiment with peat sediments collected from the Qinghai-Tibet Plateau of China to explore the effects of ferrihydrite reductionfor CH4 productions in peatlands by using geochemical analyses including 57Fe Mössbauer spectroscopy and three-dimensional fluorescence spectroscopy (3D-EEM) in combination with high-throughput sequencing of 16S rRNA and real-time fluorescence quantitative PCR (qPCR). Results showed that ferrihydrite reduction significantly increased CH4 production, being 30 times of that under the control. Selective extractions for iron oxides and 57Fe Mössbauer spectroscopy measurements revealed that no crystalline secondary iron minerals were formed during the ferrihydrite reduction process. The addition of ferrihydrite enhanced the degradation of dissolved organic matter (DOM) in peat soil, resulting in a reduction in the concentration of dissolved organic carbon (DOC). Furthermore, the relative abundance of typical fermentative microorganisms in peat sediments, including Acidobacteriota and Bacteroidota, significantly increased. Such a result indicated that reduction of ferrihydrite accelerated organic matter decomposition and increased substrate concentration required for methanogenesis. Furthermore, a co-increase in relative abundance of Geobacter, Geothrix, and Methanobacterium in the ferrihydrite-amended group suggested a potential synergistic interaction that may promote the CH4 production. Our results demonstrated that ferrihydrite reduction could significantly enhance CH4 production and play a vital role in regulating CH4 emissions in peatlands.

Earthworms in an enhanced weathering mesocosm experiment: Effects on soil carbon sequestration, base cation exchange and soil CO2 efflux

Despite its attractiveness for long-term carbon dioxide removal (CDR), quantifying weathering and CDR rates for enhanced weathering is a significant challenge. Moreover, the role of soil organisms, such as earthworms, in enhancing silicate weathering (both physically and chemically) has been suggested, but there is limited quantitative data on how biota, especially earthworms, contribute to inorganic carbon sequestration. To address these gaps, we conducted a mesocosm experiment with earthworms and basalt.Results indicate increases in clay and cation exchange, causing a weathering rate of over 10−12 mol total alkalinity m2 s−1, in range with other basalt experiments. Basalt amendment increased dissolved inorganic carbon export by only 4 g CO2 m−2. During the 4.5-month experiment, we observed neither a change in organic nor in inorganic carbon content.In soils without earthworms, basalt amendment reduced soil CO₂ efflux by approximately 0.2 kg CO₂ m2, suggesting considerable CDR. This decrease was about two times larger than calculated inorganic CDR equivalents, suggesting changes in soil organic matter dynamics.Interestingly, earthworms reversed the basalt-induced reduction in soil CO₂ efflux. This reversal was partly due to reduced export of dissolved inorganic carbon but mainly driven by increased organic matter decomposition. Our study highlights the importance of including organic carbon dynamics when evaluating the CDR potential of enhanced weathering.

Mechanism of Carbon Monoxide (CO) Generation and Potential Human Health Hazard during Mechanized Tunnel Driving in Organic-Rich Rocks: Field and Laboratory Study

The monitoring of carbon emissions is increasingly becoming a sustainability issue worldwide. Despite being largely unnoticed, the toxic gas carbon monoxide (CO) is ubiquitous in mechanized tunnel driving, but the individual sources, release and enrichment mechanisms are often unknown. In this study, the generation of CO from organic matter containing sedimentary rocks was investigated during mechanized tunnel driving and by reacting claystone and sandstone with 10 mM NaCl solutions for 2 months at 70 °C and 140 °C. The mineralogical and geochemical evolution of the solids and fluids was assessed by CO measurements and the XRD, DTA, TOC, IC and ICP-OES methods. The CO concentration in the atmosphere reached up to 1920 ppm (100 ppm on average) during tunnel driving, which is more than three times higher than the legal daily average dose for tunnellers, thus requiring occupational safety operations. Mineral-specific dissolution processes and the rapid decomposition of labile organic matter upon thermal alteration contributed to the liberation of CO and also carbon dioxide (CO2) from the host rocks. In mechanized tunnel driving, frictional heat and ‘cold’ combustion with temperatures reaching 50–70 °C at the drill head is an important mechanism for increased CO and CO2 generation, especially during drilling in sedimentary rocks containing significant amounts of OM and when the ventilation of the tunnel atmosphere and air mixing are limited. Under such conditions, human health damage due to CO exposure (HHDCO) can be 30 times higher compared to tunnel outlets, where CO is emitted from traffic.

Microbial diversity and cellulase activity of forest soils and litters

The quantity, composition and cellulase activity of forest soils and litters with deciduous and coniferous tree vegetation on the territory of Natural Park "Vitosha" were investigated. Biogenicity, the rate of decomposition of organic matter and specifically of cellulose decomposition were higher in Fagus sylvatica litters than in Pinus sylvestris. In most soil profiles, the total microflora has higher values in the mixed fermentative and humic layer of the litter compared to the fresh litter. The quantity of microorganisms and cellulase activity decrease in the depth of the soil profiles. In general, non-spore-forming bacteria, followed by mold fungi and bacilli, occupy a major share in the composition of the total microflora in litters and soils, and actinomycetes are less represented. The cellulase activity depends to the highest degree on the non-sporulating bacteria, and the values of the mineralization coefficient on the bacteria assimilating mineral nitrogen. The humidity of the litters and soils has a stronger influence on the development, composition, mineralization and cellulase activity of microorganisms, compared to the altitude.

Hydrothermal carbonization of coking sludge: Migration behavior of heavy metals and magnetic separation performance of hydrochar

This study comprehensively investigated the migration behavior and environmental risk of heavy metals (HMs) during the hydrothermal carbonization (HTC) of coking sludge (CS). The results indicated that over 90 % of HMs accumulated in the coking sludge hydrochar (CHC). The decomposition and loss of organic matter led to an increased concentration of HMs with rising temperatures. However, HTC also facilitated the transformation of HMs from bioavailable fractions to more stable fractions. Higher hydrothermal temperatures positively influenced the control of HMs' environmental risks. Ecological risk assessments revealed that the Potential Ecological Risk Index (RI) values of HMs in CHC decreased from 631.15 to 134.23, reaching considerate risk levels. Risk assessment codes indicated that, except for Mn, other HMs were reduced to no risk or low risk after hydrothermal treatment. Furthermore, the magnetic separation performance of CHC was explored, and its practical value was validated using a semi-continuous adsorption-separation device. The results showed that CHC achieved removal rates of 80.41–87.15 % for Congo red (CR) and tetracycline (TC), maintaining stability in various complex water environments. The CHC was rapidly separated after adsorption with a simple magnetic field, achieving a separation and recovery rate of over 80 %. These findings provided theoretical support for the stabilization of HMs in CS and the resource utilization of hydrochar in water treatment applications.

Microplastic contamination accelerates soil carbon loss through positive priming

The priming effect, i.e., the changes in soil organic matter (SOM) decomposition following fresh organic carbon (C) inputs is known to influence C storage in terrestrial ecosystems. Microplastics (particle size <5 mm) are ubiquitous in soils due to the increasing use and often inadequate end-of-life management of plastics. Conventional polyethylene and bio-degradable (PHBV) plastics contain large amounts of C within their molecular structure, which can be assimilated by microorganisms. However, the extent and direction of the potential priming effect induced by microplastics is unclear. As such, we added 14C-labeled glucose to investigate how background polyethylene and PHBV microplastics (1 %, w/w) affect SOM decomposition and its potential microbial mechanisms in a short-term. The cumulative CO2 emission in soil contaminated with PHBV was 42–53 % higher than under Polyethylene contaminated soil after 60-day incubation. Addition of glucose increased SOM decomposition and induced a positive priming effect, as a consequence, caused a negative net soil C balance (−59 to −132 μg C g−1 soil) regardless of microplastic types. K-strategists dominated in the PHBV-contaminated soils and induced 72 % higher positive priming effects as compared to Polyethylene-contaminated soils (160 vs. 92 μg C g−1 soil). This was attributed to the enhanced decomposition of recalcitrant SOM to acquire nitrogen. The stronger priming effect associated in PHBVs can be attributed to cooperative decomposition among fungi and bacteria, which metabolize more recalcitrant C in PHBV. Moreover, comparatively higher calorespirometric ratios, lower substrate use efficiency, and larger enzyme activity but shorter turnover time of enzymes indicated that soil contaminated with PHBV release more energy, and have a more efficient microbial catabolism and are more efficient in SOM decomposition and nutrient resource uptake. Overall, microplastics, (especially bio-degradable microplastics) can alter biogeochemical cycles with significant negative consequences for C sequestration via increasing SOM decomposition in agricultural soils and for regional and global C budgets.

Greenhouse gas emissions in response to tillage, nitrogen fertilization, and manure application in the tropics

Cultivation of maize (Zea mays L.) can emit significant greenhouse gases (GHGs) due to root respiration, soil organic matter decomposition, and fertilizer losses in a tropical environment. Our objective was to examine the effect of tillage (conventional tillage [CT], minimum tillage [MT], and no-tillage [NT]), N fertilization rate (0, 90, and 120 kg N ha−1), and manure application rate (0, 5, and 10 Mg ha−1) on CO2, N2O, and CH4 emissions under maize in two growing seasons (July-October 2018 and May-August 2019) in southwest Nigeria. We measured CO2, N2O, and CH4 fluxes using the static chamber method and soil temperature and water content weekly, global warming potential (GWP), maize yield, and greenhouse gas intensity (GHGI). The CO2 and N2O fluxes peaked immediately following planting, fertilization, and intense precipitation, with most fluxes concentrated at 2–6 wk after planting. The CH4 flux showed little change throughout the duration of the study. Cumulative CO2 and N2O fluxes were greater for CT and MT than NT, but cumulative CH4 flux was greater for MT than CT and NT. Higher N fertilization rate increased N2O and CH4 fluxes. The GWP was greater for CT than MT and NT and greater for 90 than 0 kg N ha−1. Maize yield was greater for MT than CT and NT and increased with higher N fertilization rate. The GHGI was lower for MT than CT and lower for 120 than 0 and 90 kg N ha−1. Because of overall lower maize yield, MT with reduced N ferilization rate in split applications may be needed to reduce GHG emissions while sustaining yield in the sandy soils of southwest Nigeria.

Transcriptomic analyses of bacterial growth on fungal necromass reveal different microbial community niches during degradation.

Bacteria are major drivers of organic matter decomposition and play crucial roles in global nutrient cycling. Although the degradation of dead fungal biomass (necromass) is increasingly recognized as an important contributor to soil carbon (C) and nitrogen (N) cycling, the genes and metabolic pathways involved in necromass degradation are less characterized. In particular, how bacteria degrade necromass containing different quantities of melanin, which largely control rates of necromass decomposition in situ, is largely unknown. To address this gap, we conducted a multi-timepoint transcriptomic analysis using three Gram-negative, bacterial species grown on low or high melanin necromass of Hyaloscypha bicolor. The bacterial species, Cellvibrio japonicus, Chitinophaga pinensis, and Serratia marcescens, belong to genera known to degrade necromass in situ. We found that while bacterial growth was consistently higher on low than high melanin necromass, the CAZyme-encoding gene expression response of the three species was similar between the two necromass types. Interestingly, this trend was not shared for genes encoding nitrogen utilization, which varied in C. pinensis and S. marcescens during growth on high vs low melanin necromass. Additionally, this study tested the metabolic capabilities of these bacterial species to grow on a diversity of C and N sources and found that the three bacteria have substantially different utilization patterns. Collectively, our data suggest that as necromass changes chemically over the course of degradation, certain bacterial species are favored based on their differential metabolic capacities.IMPORTANCEFungal necromass is a major component of the carbon (C) in soils as well as an important source of nitrogen (N) for plant and microbial growth. Bacteria associated with necromass represent a distinct subset of the soil microbiome and characterizing their functional capacities is the critical next step toward understanding how they influence necromass turnover. This is particularly important for necromass varying in melanin content, which has been observed to control the rate of necromass decomposition across a variety of ecosystems. Here we assessed the gene expression of three necromass-degrading bacteria grown on low or high melanin necromass and characterized their metabolic capacities to grow on different C and N substrates. These transcriptomic and metabolic studies provide the first steps toward assessing the physiological relevance of up-regulated CAZyme-encoding genes in necromass decomposition and provide foundational data for generating a predictive model of the molecular mechanisms underpinning necromass decomposition by soil bacteria.

Data transformations cause altered edaphic‐climatic controls and reduced predictability on soil carbon decomposition rates

AbstractData transformation of the reference soil organic matter (SOM) decomposition rates (kref), often derived as turnover times or in alternative formats, is commonly used to develop ecological models for projecting the persistence of SOM. However, the effects of reciprocal or logarithmic transformation of kref on model performance and edaphic‐climatic patterns remain uncertain. Here, we convert published kref values into reciprocal or logarithmic formats and establish machine learning models between the transformed kref and edaphic‐climatic predictors. We show that models trained with the transformed kref exhibit a 11.6%−68.4% reduction in performance upon re‐conversion to kref compared to those trained with the original kref. The variable importance analysis identifies distinct key predictors governing the original kref and its transformed counterparts. This suggests that data transformation alters the relative significance of predictors without necessarily improving kref prediction performance. Consequently, our study underscores the importance of directly focusing on the original values rather than alternative representations when dissecting a given variable's patterns and mechanisms in ecological modeling.

Enhanced humification attributed by the integration of Fenton reagent and oxalic acid during a co-composting of swine manure and corn straw: Impacts and the possible mechanisms

To illustrate the role and mechanism of using oxalic acid (OA) and Fenton reagent to enhance carbon transformation and humification in the co-composting of swine manure and corn straw, four different treatments, SW1 (Control), SW2 (Fenton reagent), SW3 (10 % OA), and SW4 (Fenton reagent + 10 % OA) were set up for an 80-day pilot-scale composting. Compared with the Fenton pretreatment, the contents of Fe (II) and hydroxyl radicals (·OH) in the SW4 treatment increased by 20.25 %-54.55 % and 6.39 %-71.00 %, respectively. This confirmed the role of OA in protecting Fe (II) and maintaining the generation of ·OH during the composting. Compared with Control, Fenton-like reagent amendment facilitated decomposition of dissolved organic carbon and total organic matter by 20.53 % and 25.37 %, respectively, which led to a higher content of humic substances (141.81 mg/g) and a higher degree of polymerization (3.51) in SW4. Among all, the dissolved organic carbon in the compost substrate of SW4 treatment showed the highest level of aromatization and more refractory organic matter decomposition. The compact microbial co-occurrence network analysis exhibited the high-metabolic activity in Fenton-like treatment (SW4). Therefore, the probable mechanism of humification facilitation by Fenton-like reagent amendment in co-composting could be controlled by several processes: 1) generation of ·OH for facilitating the decomposition of organic matter, 2) disintegration of refractory lignocellulose substances by promoting the lignin pathway of humification, and 3) increasing the quantity and activity of microbes (i.e., Proteobacteria, Actinobacteriota, Chloroflexi, Ascomycota and Basidiomycota) involved in humification. This study provided a profound understanding of Fenton-like reagent amendments in co-composting of agricultural solid wastes and proposes a solution for enhancing the humification degree of compost products for agricultural use.