Soil Processes Research Articles

Palaeosols and surfaces: what fossil soils tell us about the representation of time in some sedimentary successions

Soils and hence palaeosols develop at geomorphic surfaces comprising landscapes. As most develop they reorganize the substrate to create texturally and chemically defined units (horizons) parallel to the land surfaces and some of these horizons become lithified resembling beds. Palaeosols, in many cases do not represent hiatuses but developed during deposition and represent condensation not lost time. The degree of pedogenic reorganization can be used to estimate the temporal significance of the length of soil formation but soils are commonly polygenetic and have not followed a simple, time-related developmental pathway. The complexity of soil development is illustrated with reference to the late Silurian-early Devonian polyphase alluvial palaeosols from South Wales which provide an example of how dynamic changes in sedimentation and erosion have occurred without changes in soil processes. The significance of these polyphase palaeosol profiles is reviewed in the broader context of mid Palaeozoic landscape changes.

The Influence of Fibers from Domestic Laundry Wastewater on the Clogging Process of a Filter

This study presents the impact of the size and shape of particles in laundry wastewater on the clogging process of a porous material. Clogging can be defined as a mechanical limitation of flow through porous media. The process of mechanical clogging was investigated in this study. The research was conducted in laboratory conditions in a filter column filled with glass beads whose diameter corresponded to coarse sand. The results reveal the influence of graywater quality on filter hydraulic conductivity and bed clogging, showing the impact of fiber particles in wastewater (sewage from home laundry) on the clogging process in soil. The results confirm that fiber particles significantly reduce filter permeability, particularly due to the formation of a filter cake. As analyzed in this paper, the distribution of quantitative data on particles of different sizes found in laundry wastewater indicates that they mainly accumulate in the upper layer, where particles with fiber lengths ranging from 0 to 1600 µm can be found. The average length of the fibers decreased with increasing depth. At a depth of approximately 10 cm, fibers with dimensions in the range of 0 to 100 μm were predominantly observed.

Nitrogen enrichment stimulates nutrient cycling genes of rhizosphere soil bacteria in the Phoebe bournei young plantations

Anthropogenic nitrogen (N) deposition is expected to increase substantially and continuously in terrestrial ecosystems, endangering the balance of N and phosphorus (P) in P-deficient subtropical forest soil. Despite the widely reported responses of the microbial community to simulated N deposition, there is limited understanding of how N deposition affects the rhizosphere soil processes by mediating functional genes and community compositions of soil bacteria. Here, five levels of simulated N deposition treatments (N0, 0 g m−2·yr−1; N1, 100 g m−2·yr−1; N2, 200 g m−2·yr−1; N3, 300 g m−2·yr−1; and N4, 400 g m−2·yr−1) were performed in a 10-year-old Phoebe bournei plantation. Quantitative microbial element cycling smart chip technology and 16S rRNA gene sequencing were employed to analyze functional gene compositions involved in carbon (C), N, and P cycling, as well as rhizosphere bacterial community composition. N deposition significantly influenced C cycling relative abundance of genes in the rhizosphere soil, especially those involved in C degradation. Low and moderate levels (100–300 g m−2·yr−1) of N deposition promoted the relative abundance of the C decomposition-related genes (e.g., amyA, abfA, pgu, chiA, cex, cdh, and glx), whereas high N deposition (400 g m−2·yr−1) suppressed enzyme (e.g., soil invertase, soil urease, and soil acid phosphatase) activities, affecting the C cycling processes in the rhizosphere. Simulated N deposition affected the functional genes associated with C, N, and P cycling by mediating soil pH and macronutrients. These findings provide new insights into the management of soil C sequestration in P. bournei young plantations as well as the regulation of C, N, and P cycling and microbial functions within ecosystems.

Applying minirhizotrons to observe spatiotemporal variations in rooting depth and distribution in agroecosystems to improve the performance of hydrological models

AbstractTo understand and explain soil moisture dynamics, the role of the vegetation is crucial. Hydrological processes in agricultural soils are strongly affected by rooting depth and root distribution. We present a new approach to monitor and model root dynamics and its influence on soil moisture using minirhizotrons combined with phenological observations. Field setups consist of a portable root scanner and acrylic glass tubes installed in the soil at the start of the growing season. 360° scans of soil and roots are taken regularly at different depths in the tubes. Root traits are identified automatically for each soil layer and complemented by observations of aboveground plant phenology. Results from minirhizotron data collected at an agrometeorological observatory in Germany show for both cereal and rapeseed (Brassica napus L.) crops a higher root density in deeper soil layers and a lower density near the soil surface when compared to literature data. An opposite picture emerged for maize (Zea mays L.) and potato (Solanum tuberosum L.), whereas vertical root distribution in sugar beet (Beta vulgaris subsp. vulgaris) had a different seasonal course than expected from literature. Applying the new root distribution data in calculations of the soil water balance resulted in differences of more than 3% in absolute volumetric soil water content. A comparison with in situ measurements of volumetric soil moisture at 20‐ and 50‐cm depth revealed a significant improvement of the model results due to the new parameterization. Thus, we argue that minirhizotrons constitute a useful supplement to hydrological observatories and can help understand and predict soil moisture dynamics in the critical zone.

WGAN-Based Realization Process of Gravel Soil for Hydraulic Property Simulation

Gravel soil faces significant engineering challenges such as leakage erosion and soil flow due to its complex composition and susceptibility to groundwater effects. This study integrates the entire machine learning process, including pre- and post-processing of images, WGAN implementation, and validation of hydraulic and morphological properties. Obtaining intact gravel soil samples is difficult and costly due to their erodible nature in the Li River, China. A μ-CT scanning series is employed to capture detailed images with three microstructural characteristics of gravel soil, forming the basis for training datasets using WGANs. This approach allows the generation of similar 3D realizations that replicate the microstructural characteristics and hydraulic behaviors of a prototype of gravel soils. Through computational fluid dynamics (CFD) simulations, the effectiveness of the realizations in hydraulic behavior within reconstructed porous structures is verified. This process indirectly validates the consistency between the realization′s microstructure and the prototype. This integrated methodology not only enhances understanding but also aids in the optimization of engineering designs and applications in geotechnical and materials science disciplines.

Interplay between vanadium distribution and microbial community in soil-plant system

Soil-plant system play an essential role in distribution and transformation of vanadium (V). V shapes the diversity of soil communities, while soil microorganisms mediate V transformation. Plants also absorb V from surrounding soil. However, the study of microbial response to V stress in different soil-plant compartments is limited, and the metabolic functions driving V transformation across these systems remain elusive. The study investigates the distribution of V in soil-plant systems nearby a V smelter. 16S rRNA sequencing and metagenomics are utilized to reveal the microbial adaptation and V transformation in bulk soil, rhizosphere, and endosphere. Bothriochloa ischaemum (L.) Keng. (BK) exhibits higher phytoextraction potential (TF = 0.74 ± 0.26). Environmental variables, including pH, V, OM, and AP, show significant (p < 0.05) influence in soil community composition, with homogeneous selection governing the assembly processes in bulk soil and rhizosphere, while stochastic process dominates endospheric assembly. Metagenomic investigation revealed a coordinated metabolic pathway between functional taxa in soil and plants, which lead to root uptake and translocation. V stress is mitigated through Nocardioide, Microvirga, and Solirubrobacter, putatively harboring V(V) reduction genes n arG and mtrC in soil. In rhizosphere, citrate synthase gltA and alkaline phosphatase phoD exhibit functional potential to facilitate formation of V-complexation to increase V mobility. In endoshere, endophytic Enterobacter further detoxifies V(V), and likely promotes V translocation through siderophore biosynthesis gene, iucA. These findings enhance our understanding on interplay between V and microbial community in soil-plant systems, which is instrumental in developing mitigation plan for V contaminated sites.

Litter Chemistry Is a Main Driver of Inorganic Nitrogen in Disturbed Soils in the Arid Patagonian Monte

ABSTRACTChanges in plant cover and soil characteristics induced by grazing may affect litter quality and nitrogen (N) release under varying abiotic conditions. Our study was focused on the importance of litter chemistry as a main driver of inorganic N (ammonium‐N: NH4+‐N and nitrate‐N: NO3−‐N) release to soil. Both inorganic N forms are important components for N availability to plants and soil processes, and the long‐term conservation of soil‐N fertility. We analyzed the effect of secondary compounds and the C/N ratio in litter under varying soil water, and UV exposure on soil inorganic N (NH4+‐N and NO3−‐N) in Patagonian Monte degraded soils. We hypothesized that secondary compounds and C/N ratio in litter are main drivers of soil inorganic N under varying abiotic conditions. We conducted a microcosm experiment (13 months) using intact upper soil blocks from denuded soil areas. Surface soils were added with shrub (SL), and mixed grass and shrub (GSL) litter with high versus low secondary metabolites concentration and low vs. high C/N ratio, respectively. Microcosms were maintained under ambient and reduced UV exposure, and high and low soil water. We used microcosms without litter as controls. Monthly, we assessed NH4+‐N and NO3−‐N concentrations in upper and sub‐superficial soils. Litter chemistry interacting with abiotic factors did not significantly influence soil NH4+‐N at any soil depth while litter chemistry was a main driver of NO3−‐N in upper soil. SL enhanced NO3−‐N in upper soil compared with GSL independently of abiotic factors. In upper soils without litter and in those with GSL, the highest NO3−‐N concentration occurred mostly under high soil water and exposition to UV. We concluded that litter chemistry was a main driver of soil N fertility in disturbed rangelands. Shrub litter may enhance N fertility (NO3−‐N) in degraded soils.

Atmospheric Trace Gas Oxidizers Contribute to Soil Carbon Fixation Driven by Key Soil Conditions in Terrestrial Ecosystems.

Microbial oxidizers of trace gases such as hydrogen (H2) and carbon monoxide (CO) are widely distributed in soil microbial communities and play a vital role in modulating biogeochemical cycles. However, the contribution of trace gas oxidizers to soil carbon fixation and the driving environmental factors remain unclear, especially on large scales. Here, we utilized biogeochemical and genome-resolved metagenomic profiling, assisted by machine learning analysis, to estimate the contributions of trace gas oxidizers to soil carbon fixation and to predict the key environmental factors driving this process in soils from five distinct ecosystems. The results showed that phylogenetically and physiologically diverse H2 and CO oxidizers and chemosynthetic carbon-fixing microbes are present in the soil in different terrestrial ecosystems. The large-scale variations in soil carbon fixation were highly positively correlated with both the abundance and the activity of H2 and CO oxidizers (p < 0.05-0.001). Furthermore, soil pH and moisture-induced shifts in the abundance of H2 and CO oxidizers partially explained the variation in soil carbon fixation (55%). The contributions of trace gas oxidizers to soil carbon fixation in the different terrestrial ecosystems were estimated to range from 1.1% to 35.0%. The estimated rate of trace gas carbon fixation varied from 0.04 to 1.56 mg kg-1 d-1. These findings reveal that atmospheric trace gas oxidizers may contribute to soil carbon fixation driven by key soil environmental factors, highlighting the non-negligible contribution of these microbes to terrestrial carbon cycling.

Identifying and quantifying the contribution of maize plant traits to nitrogen uptake and use through plant modelling

Abstract Breeding for high nitrogen use efficient crops can contribute to maintaining or even increasing yield with less nitrogen. Nitrogen use is co-determined by N uptake and physiological use efficiency (PE, biomass per unit of N taken up), to which soil processes as well as plant architectural, physiological and developmental traits contribute. The relative contribution of these crop traits to N use is not well known but relevant to identify breeding targets in important crop species like maize. To quantify the contribution of component plant traits to maize N uptake and use, we used a functional-structural plant model. We evaluated the effect of varying both shoot and root traits on crop N uptake across a range of nitrogen levels. Root architectural traits were found to play a more important role in root N uptake than physiological traits. Phyllochron determined the structure of the shoot through changes in source: sink ratio over time which, in interaction with light and temperature, resulted in a significant effect on PE and N uptake. Photosynthesis traits were more relevant to biomass accumulation rather than yield, especially under high nitrogen conditions. The traits identified in this study are potential targets in maize breeding for improved crop N uptake and use.

How different soil surface treatments in urban areas affect soil pore structure and associated soil properties and processes

Soil water and temperature regimes in urban environments are greatly affected by different surface treatments, and these may lead even to changes in soil properties. The goal of this study was to find out how soil properties had changed after 8 years of soil surface modification. Five surface treatment scenarios were considered: bare soil (BS), bark chips (BC), concrete paving (CP), mown grass (MG), and unmown grass (UG). X-ray computed tomography and micromorphological analyses showed that character of pores in soils with grass (MG, UG), which were mainly influenced by organisms living in soils and roots, differed from pore character in soil covers BC or CP, which mostly were impacted by organisms living in soils. Both groups differed from BS, which was predominantly affected by the regular treatment consisting in weed removal and soil loosening. Soil under BC was more compact than for other treatments due to decomposition of the bark chips mulch and migration of mulch components. Organic matter content was greatest but its quality lowest in the BC soil, followed by UG, MG, CP, and BS. The highest aggregate stability assessed using the water-stable aggregates (WSA) index was found for UG, followed by MG, BC, CP, and BS. The greatest water retention ability was observed for BC followed by UG, MG, CP, and BS. The unsaturated hydraulic conductivities for pressure head of –2 cm measured for UG, MG, and BS were much higher than were those for CP and BC. Finally, the greatest net CO2 efflux was measured for BC and MG, followed by UG, CP, and BS. CO2 emission correlated negatively with soil physical quality expressed as slope of the soil water retention curve at its inflection point. In general, the best soil conditions were observed for UG. No treatment considerably aggravated soil condition.

Biodegradation Study of Food Packaging Materials: Assessment of the Impact of the Use of Different Biopolymers and Soil Characteristics

In this article, the relationship between the properties of different membranes (agar, chitosan, and agar + chitosan) and biodegradability in natural and sterilized soil was investigated. The membranes under investigation exhibited variations in the biodegradation process, a phenomenon closely linked to both the soil microbiota composition and their water affinity. Higher solubility in water and greater swelling tendencies correlated with shorter initiation times for the biodegradation process in soil. Overall, all tested membranes began biodegradation within 14 days, as assessed through thickness and morphological analysis parameters, demonstrating a superior degradation rate compared to low-density polyethylene films.

Exploring soil pedogenesis through frequency-dependent magnetic susceptibility in varied lithological environments

AbstractThe use of percent frequency-dependent magnetic susceptibility (χfd%) is well-established for detecting superparamagnetic (SP) components in fine-grained soils and sediments. This study employs χfd% as a direct indicator of pedogenetic processes in soils from the Moroccan Rif region. Three soil transects (T1, T2, and T3), each comprising four soil cores with depths reaching 100 to 120 cm, were sampled from distinct lithological formations within an area subject to moderate to intense erosion. A total of 272 soil samples were collected and analyzed using MS2 Bartington Instruments, providing values to calculate χfd% and identify ultrafine ferrimagnetic minerals (SP, &lt; 0.03 μm). In Quaternary fluvial terraces (T1) soils, approximately 60% of the samples indicate a mixture of SP, multidomain (MD), and Single Stable Domain (SSD) magnetic grains, while 30% contained coarser MD grains. Only 10% of the samples exhibit predominantly superparamagnetic (SP) grains. Soils on marly substrates (T2) showed 90% of samples with a combination of SP, MD, and SSD, and just 10% had SP grains. In contrast, soils from Villafranchian sandy deposits displayed χfd% values exceeding 10% in over 50% of samples, indicating that almost all iron components consist of SP grains. Physico-chemical analyses of the soils in profiles T1, T2, and T3 reveal distinct characteristics, including variations in clay content, organic matter, nutrient levels, and proportions of free and total iron. These results are important for understanding soil evolution and pedogenesis, with profiles T1 and T3 showing advanced development marked by high mineral iron, clay, and organic matter content. In contrast, profile T2 reflects a weak stage, influencing nutrient availability and contributing to overall soil dynamics in the respective profiles. The results of this study suggest that magnetic susceptibilities in these samples primarily originate from pedogenetic sources, revealing significantly advanced pedogenesis compared to T1 and T2 soils. The findings of this study align with previous research on soil erosion and degradation in the region, demonstrating that soils developed on terraces and marly substrates are more degraded and less stable than those on sandy substrates. This study underscores the utility of magnetic susceptibility as a rapid and effective indicator for initial soil assessment and gauging the degree of pedogenesis.

Reconciling plant and microbial ecological strategies to elucidate cover crop effects on soil carbon and nitrogen cycling

Abstract Plant economics, the way plants allocate and utilize resources, affect multiple soil processes through interactions with root and associated microbial communities. However, the interplay between plant economics and microbial ecological strategies remains poorly understood, which is crucial for integrated manipulation of plant‐ and microbe‐mediated functions in mitigating climate change and sustaining soil health. We used a field experiment with 11 cover crop species grown monocultures in the same base soil to test whether microbial ecological strategies are associated with plant economic strategies and if their interactions are linked to soil functions. A principal component analysis (PCA) was performed on root and leaf traits to identify the loadings of cover crop species on the plant trait space. Metagenomic analysis of rhizosphere microbial communities was conducted to infer their ecological strategies based on genetically encoded community‐aggregated traits. We found a synchronous relationship between the conservation gradient of plant economic strategies and the trade‐offs in microbial ecological strategies. Conservative plant strategists, such as Lolium multiflorum, Triticum turgidum and Brassica juncea, fostered microbial communities characterized by high growth yield potentials (Y‐strategies). This included increased microbial carbon fixation pathways, citrate cycle, ribosome and valine, leucine and isoleucine biosynthesis. As a result, microbial metabolic efficiency improved, shown by higher microbial biomass carbon content and a lower metabolic quotient (qCO2), led to enhanced soil organic carbon accumulation. In comparison, acquisitive plants like Astragalus sinicus, Vicia villosa, Trifolium incarnatum and Medicago sativa stimulated microbial resource‐acquisition strategies (A‐strategies). This included enhanced bacterial chemotaxis, secretion systems, biotin metabolism and cell motility pathways, which in turn increased soil exoenzyme activity and accelerated soil nitrogen mineralization. Consequently, these species enhanced soil nitrogen availability and had substantial feedbacks on subsequent main crop productivity. Synthesis. This study demonstrates how plant economic strategies influence the balance between different microbial ecological strategies, specifically the trade‐offs in Y‐ and A‐strategies. These interactions exert control over carbon and nitrogen dynamics in the soil ecosystem. The findings provide insights for implementing nature‐based solutions to improve agroecosystem management practices.

Determining the Soil Particle Shape by Use of Dynamic Image Analysis

In Soil Science, it is well established that the geometry of individual soil particles, including their shape and size, has a significant impact on a number of key physical properties of the soil and on the processes involved with it. The shape and size of soil particles directly impact aspects such as permeability, water retention, stability of soil aggregates and the availability of nutrients for plants. Therefore, accurate determination of these characteristics of soil particles becomes extremely important for understanding and effective soil management. Nowadays, dynamic image analysis (DIA) is emerging as an exceptionally versatile and effective technique that enables precise determination of particle characteristics, including shape and size, in a dynamic and non-invasive manner. DIA enables the automatic analysis of thousands of microscopic images, allowing rapid and accurate study of the morphology of soil particles at micro and macro scales. The use of dynamic image analysis in soil research provides insight into the complex structures of soil particles and better prediction of their impact on various soil processes. Moreover, DIA enables the examination of a large number of samples in a short time, which contributes to the efficiency and precision of soil testing. Therefore, dynamic image analysis is becoming a widely used technique for determining particles' characteristics, such as shape and size. In the context of an ever-increasing awareness of the sustainable use of natural resources and the need to optimize agricultural and engineering practices, dynamic image analysis is becoming an indispensable tool for soil scientists, environmental scientists and engineers. Its versatile use can contribute to further expanding our knowledge about soil and developing innovative solutions for sustainable soil and environmental management.

Silicon Ameliorants from Serpentine-containing Mining Waste

The results of research aimed at developing a method for using serpentine-containing mining waste as silicon ameliorants are presented. The effect of introducing the initial and thermally activated serpentine mineral lizardite and silica gel into peat soil on the chemical composition of plants was studied. The effectiveness of materials as a source of silicon for plants was determined. It was concluded that serpentines affect soil processes in a similar way to traditional silicon preparations, which makes it possible to utilize serpentine-containing mining waste as silicon ameliorants.

Ecological practices increase soil fertility and microbial diversity under intensive farming

Intensive farming offers a potential solution to feed the growing population due to its high productivity. Conventional management (CO) based on inorganic fertilization practices degrades soil quality, but restorative practices including ecological intensification (EI) and organic management results in maintaining soil quality without compromising productivity. In this paper, two different management systems were evaluated: CO, based on inorganic fertilization, and EI, focused on providing organic nutrients to soils to support crops.EI increased soil fertility, together with higher alpha diversity indices, more differentially abundant amplicon sequence variant (ASVs) (247 EI vs. 165 CO) and indicator taxa (60 EI vs. 32 CO). Distinct bacterial taxa were associated with the different management systems, revealing their roles in soil processes and nutrient availability. In the CO treatment, indicator genera such as Nitrospira and Desulfarculaceae were linked to N fertilization and nitrite oxidation, while RB41 was associated with phosphorus availability. Ammoniphilus, PAUC26f, and BSV26 were also indicators of CO management. Conversely, EI treatment promoted bacteria involved in organic matter decomposition and nutrient cycling, such as Halomonas, Chryseolinea and Rhodobacteraceae. Gemmatimonas, Steroidobacter, Altererythrobacter, Acidibacter and Anseongella contribute to carbon and nitrogen cycling. Burkholderiaceae and Rhodopirellula play roles in phosphate solubilization and organic P mineralization, respectively. Numerous taxa with plant growth-promoting (PGP) attributes, such as BIrii41, Pseudomonas, and Lysobacter, were also identified as indicators of the EI treatment.EI associated bacteria were positively correlated with soil organic carbon contents, nitrates, and exchangeable bases, while negatively correlated with CO bacteria. A distance-based multivariate multiple regression (DistLM) demonstrated a strong relationship (r2 = 0.78) between soil physicochemical variables and bacterial community structure, with SOC explaining the most variations in the model. Other significant parameters included potassium (K), electrical conductivity (EC), and nitrates. The results suggest that EI promotes more sustainable soils in terms of fertility and microbial diversity.

Degradation of non-phthalate plasticisers in soils by liquid chromatography coupled to high resolution mass accuracy spectrometry: A comparison with sterile soil

The market for non-phthalate plasticisers (NPPs), such as adipates, citrates, phosphates, and carboxylates, has grown due to their low toxicity, but no studies have determined their metabolites during degradation processes in soil. This study evaluated the degradation of diethyl hexyl adipate (DEHA) and acetyl triethyl citrate (ATEC) in nonsterile soil, and the results were compared with those obtained from sterile soil, to determine whether microbial activity causes degradation in these NPPs. The analyses of these substances were performed using liquid chromatography coupled with quadrupole-Orbitrap high-resolution mass spectrometry (LC-Q-Orbitrap-HRMS). Plasticiser degradation followed a biphasic kinetic model, with a half-life time (DT50) of 9–12 days in non-sterile soil, but very slow in sterile soil (DT50 > 58 days). The degradation of target plasticisers in nonsterile soil resulted in the detection of eight metabolites of DEHA and ATEC, which were not detected in sterile soil. Among them, 4-[(2-ethylhexyl)oxy]-4-oxobutanoic acid (EHOBA), 4-((2-ethylhexyl)oxy)-4-oxo-1-carbonyl hexanoate (EHOCH), triethylcitrate (TEC) and N-acetyl glutamine (NAG) have been detected for the first time in this study. Most of these metabolites were detected after 14 days, increasing their concentration to 21 days, before completely degrading after 45 days. Nevertheless, mono–2-ethyl-5-hydroxyhexyl adipate (MEHHA), mono-2-ethyloxohexyl adipate (MEHOA), EHOCH, and diethyl citrate (DEC) were persistent in non-sterile soil (detected at 45 days) with an LD50 lower than their respective original molecules. Therefore, it is necessary to control the amount of these metabolites derived from the degradation of this type of plasticisers in the soil to avoid health risks, as they can end up in vegetables.

Microbial inoculants using spent mushroom substrates as carriers improve soil multifunctionality and plant growth by changing soil microbial community structure

Peat is typically used as a carrier for microbial inoculants; however, due to its non-renewable nature alternatives need to be identified as reliable and renewable carriers for mineral-solubilizing inoculants. In pot experiments, solid microbial inoculants were comprised of peat (P), biochar (BC), and spent mushroom substrates (SMS) using Medicago sativa L. as experimental materials, and the purpose of this study is to assess the effect of solid microbial inoculants on soil multifunctionality and plant growth. The results revealed that the SMS microbial inoculant had the greatest positive impact on plant biomass and significantly stimulated soil multifunctionality which is typically managed or assessed based on various soil functions or processes that are crucial for sustaining productivity, in contrast to the peat microbial inoculant, particularly at a supply level of 100 g/pot. There was no significant correlation between soil multifunctionality and bacterial/fungal microbial diversity. However, according to the co-occurrence network of bacteria and fungi, soil multifunctionality was intimately correlated with the biodiversity of the main ecological clusters (modules) of bacteria and fungi, rather than to the entire soil microbial community structure. The keystone species of module hubs and connectors play critical roles in maintaining the stability of ecological clusters of microbial co-occurrence networks and linkages between ecological clusters. Soil pH is a major predictor of changes in plant biomass, and leads to changes therein by affecting the major ecological clusters of bacterial and fungal co-occurrence networks. These results suggested that SMS may serve as a good alternative to peat as a carrier of mineral-solubilizing microorganisms to maintain soil multifunctionality and promote plant growth.

Effects of manure and nitrogen fertilization on soil microbial carbon fixation genes and associated communities in the Loess Plateau of China

The effects of long-term fertilization on soil carbon (C) cycling have been a key focus of agricultural sustainable development research. However, the influences of different fertilization treatments on soil microbial C fixation profiles are still unclear. Metagenomics technology and multivariate analysis were employed to inquire changes in soil properties, soil microbial C fixation genes and associated bacterial communities, and the influence of dominant soil properties on C fixation genes. The contents of soil C and nitrogen fractions were signicficantly higher in manure or combined with nitrogen fertilization (NM) than other treatments. The composition of soil microbial C fixation genes and associated bacterial communities varied among different fertilization treatments. Compared with other treatments, the total abundance of microbial C fixation genes and the abundance of Proteobacteria were significantly higher in NM than in other treatments, as well as the abundances of C fixation genes involved in dicarboxylate/4-hydroxybutyrate cycle and reductive citrate cycle. Key functional genes and main bacterial communities presented in the middle of the co-occurrence network. Soil organic carbon, total nitrogen, and microbial biomass nitrogen were the dominant soil properties influencing microbial C fixation genes and associated bacterial communitis. Fertilization increased the abundance of C fixation genes by affecting the changes in bacterial communities abundance mediated by soil properties. Overall, elucidating the responses of soil microbial C fixation genes and associated communities to different fertilization will enhance our understanding of the processes of soil C fixation in farmland.

Study on the extension mechanism of fissures in expansive soil based on fracture mechanics test method

Expansive soil, characterized by widespread fissures, is a special type of soil prone to localized fissure propagation, leading to failure and instability, often resulting in landslides. Numerous studies have applied fracture mechanics theory to analyze soil failure along fissures, but no standardized testing method has been established. This paper reviews existing soil fracture toughness testing methods, designs an integrated system combining digital image correlation(DIC) technique and electrical resistance testing, and employs the Cracked Chevron-Notched Brazilian Disc (CCNBD) method to assess the fracture toughness of expansive soil. The deformation and internal damage accumulation processes of the specimens were monitored. The KΙc and KΙΙc of expansive soil were tested at moisture contents of 15 %, 20 %, and 25 % using specimens with three different crack length ratios (a/R). The role of water was explored by injecting water into the fissures. The results showed that KΙc of expansive soil ranged from 10 to 36 kPa·m0.5, with a linear negative correlation to moisture content and a proportional relationship to tensile strength, having a proportionality coefficient of 0.331. The KΙΙc ranged from 20 to 70 kPa·m0.5,and it is greater than KΙc under the same conditions. Based on the load, internal damage, strain, and fissure area during the tests, the failure process of expansive soil along fissures was divided into four stages: initial deformation stage(I), quasi-elastic deformation stage(II), fissure extension stage(III), and failure stage(IV). Water injection into the fissures reduced the soil's fracture toughness, with a more significant reduction as a/R increased and the failure showed progressive behavior. The CCNBD method, combined with DIC technique and electrical resistance testing, effectively measures the fracture toughness of soil, aiding in understanding the failure mechanism along fissures and providing a basis for preventing and controlling landslides and other hazards in expansive soils.