Organic Aggregates Research Articles

Fluorescence enhancement of organic aggregates induced by bromine substituents: Heavy-atom effect and vibronic coupling

Organic fluorophores are essential for organic optoelectronic and bioelectronic applications. Heavier halogens have been found to enhance fluorescence of organic aggregates, breaking the traditional view that heavy-atom effect leads to fluorescence quenching. Herein, we proposed that the bromine atoms show a limited acceleration to intersystem crossing (ISC) process, but largely reduce the vibronic coupling of singlet excitons, by inspecting TPE fluorophores and brominated analogs, achieving fluorescence enhancement of bromo-organic aggregates. This is because the lowest singlet excited state S1 have lower energy than triplet state T2 and large gap ΔEST with T1, and strong oscillator strength. Moreover, the excited-state dynamics further demonstrate that the bromine substituents hugely decelerate the internal conversion process, and make a slow ISC rates (∼106 s−1), in contrast to the fast radiative transition (∼108 s−1), which is responsible for the abnormal fluorescence enhancement in brominated organic aggregates.

Investigation of clay-oil interfacial interactions in petroleum-contaminated soil: Effect of crude oil composition

Crude oil, a multi-component complex organic aggregate, causes petroleum-contaminated soil (PCS) with complex properties, which makes PCS unable to achieve rapid and effective oil-soil separation. Therefore, it is crucial to investigate the impact of different crude oil components on oil-soil interactions in PCS. In this study, crude oil was divided into SARA, saturates (S), aromatic (Ar), resin (R) and asphaltene (As) in accordance with polarity and solubility to explore their thermal desorption and thermal variation of adsorption on the kaolinite (Kln) surface. Moreover, the detailed sources of the interactions were investigated using the oil-clay interfacial free energies and interfacial forces. Furthermore, molecular dynamics (MD) simulations were performed to gain insight into the interfacial interaction mechanisms. The results indicated that the polarity of SARA components followed an order of As > R > Ar > S, and the temperature required for thermal desorption and the heat released during oil-clay adsorption increased with an increase in polarity. The van der Waals forces dominated oil-clay interactions. The benzene ring and heteroatom (N, O, and S) in the polar components facilitated the oil-clay van der Waals interactions. Besides van der Waals, the higher number of benzene rings led to the generation of electrostatic interactions as well as hydrogen bonding between heteroatoms and the –OH of Kln, thus increasing the free energy and force at the oil-clay interface. The result of MD was consistent with the experimental results, thus suggesting that van der Waals, electrostatic forces, and hydrogen bonds reliably exist during the interaction between polar oil molecules and clay. Simultaneously, the oil-clay binding energies increased with higher polarity. These findings provide guidance on developing advanced oil-clay separation processes.

The impact of agricultural management on soil aggregation and carbon storage is regulated by climatic thresholds across a 3000 km European gradient.

Organic carbon and aggregate stability are key features of soil quality and are important to consider when evaluating the potential of agricultural soils as carbon sinks. However, we lack a comprehensive understanding of how soil organic carbon (SOC) and aggregate stability respond to agricultural management across wide environmental gradients. Here, we assessed the impact of climatic factors, soil properties and agricultural management (including land use, crop cover, crop diversity, organic fertilization, and management intensity) on SOC and the mean weight diameter of soil aggregates, commonly used as an indicator for soil aggregate stability, across a 3000 km European gradient. Soil aggregate stability (-56%) and SOC stocks (-35%) in the topsoil (20 cm) were lower in croplands compared with neighboring grassland sites (uncropped sites with perennial vegetation and little or no external inputs). Land use and aridity were strong drivers of soil aggregation explaining 33% and 20% of the variation, respectively. SOC stocks were best explained by calcium content (20% of explained variation) followed by aridity (15%) and mean annual temperature (10%). We also found a threshold-like pattern for SOC stocks and aggregate stability in response to aridity, with lower values at sites with higher aridity. The impact of crop management on aggregate stability and SOC stocks appeared to be regulated by these thresholds, with more pronounced positive effects of crop diversity and more severe negative effects of crop management intensity in nondryland compared with dryland regions. We link the higher sensitivity of SOC stocks and aggregate stability in nondryland regions to a higher climatic potential for aggregate-mediated SOC stabilization. The presented findings are relevant for improving predictions of management effects on soil structure and C storage and highlight the need for site-specific agri-environmental policies to improve soil quality and C sequestration.

Effects of Vegetation Restoration on Soil Organic Carbon Sequestration and Aggregate Stability in Water-Eroded Environment: A Meta-analysis

In order to clarify the differences in the effects of vegetation restoration strategies on soil carbon sequestration and aggregate stability under different water-eroded environments, we collected experimental data from 91 papers and evaluated the response of soil organic carbon (SOC) stock and aggregate stability to vegetation restoration based on Meta-analysis. The results showed the following:① compared with cropland or bare land, forestland/grassland restoration was beneficial to increase SOC stock and improve aggregate stability, but the dominant functions of the two were different. The effect of forestland restoration on carbon sequestration was stronger than that of grassland reforestation, and the effect of grassland restoration on aggregate stability was stronger than that of forestland restoration. ② Multi-factor Meta-analysis showed that the factors that significantly affected SOC were restoration year, soil clay content, vegetation coverage, mean annual precipitation (MAP), mean annual temperature (MAT), and soil depth. The positive effect of vegetation restoration on SOC stock increased with the increase in vegetation coverage rate. Grassland restoration had a more significant effect on SOC stock when soil clay content was 20%-32%, it was more likely to promote the carbon sequestration effect of grassland when MAP>800 mm or MAT<15℃, and there was no significant change in SOC stock under different restoration years. However, the effect of forestland restoration on SOC stock was more significant when soil clay content was>32%. Climate conditions had no limited effect on SOC stock in forestland, and there was a positive effect between SOC stock under forestland restoration and restoration years. ③ Vegetation restoration had stronger significant positive effects on mean weight diameter (MWD) and mean geometric diameter (GMD) when the clay content was 20%-32%, and MWD and GMD increased with the increase in vegetation coverage. ④SOC stock growth could explain 25% and 24% of the variation in the effect value of MWD and GMD, respectively. These results indicated that the formation of SOC was the result of multiple factors, and soil aggregate stability was limited only by vegetation coverage and soil clay content. The increase in SOC stock could promote the improvement of water stability MWD and GMD. These results can clarify the carbon sequestration effect of different vegetation restoration measures in water-eroded environments and provide theoretical reference for the restoration and reconstruction of degraded ecosystems.

Organic carbon accumulation and aggregate formation in soils under organic and inorganic fertilizer management practices in a rice–wheat cropping system

Soil organic carbon (C) and aggregates are the important components of soil fertility and the foundation of sustainable agriculture. The storage and protection of SOC in aggregates is widely regarded as the material basis of soil organic C accumulation. However, current understanding of soil aggregate and its associated organic C is insufficient to elucidate the regulation mechanism of soil organic C. A nine-year field experiment including chemical fertilizer (FR) and organic manure (OM) treatments was set up in the eastern plain of Funiu Mountain, central China. Using chemical analysis, physical sieving as well as nuclear magnetic resonance (NMR) methods, we mainly probed into the response of soil organic C concentration and composition, and C functional groups, water-stable aggregates to different treatments. Furthermore, scanning electronic microscopy (SEM) and partial least square structural equation modelling (PLS-SEM) was conducted to characterise the different size aggregates and to analyse the mechanism of soil organic C accumulation and stabilisation at aggregate scales. After nine years of farming, OM treatment substantially increased soil organic C content (by 3.77 g kg−1) and significantly enhanced the formation of macro-aggregates (> 250 μm), while FR had no significant influence on soil organic C. At the aggregate scale, the amounts of soil organic C, C physical fractions (particulate and mineral-associated organic C), total nitrogen and microbial biomass carbon associated in macro-aggregates (> 250 μm) were obviously higher than that in micro-aggregates and silt + clay fraction, and OM treatment greatly increased the accumulation of soil organic C and its components in macro-aggregates. Moreover, microbial biomass carbon (MBC) amounts in aggregates were remarkably increased (27–116%) by the application of OM. And MBC had a positively effect on the physical fractions of SOC but not on the C chemical structure within aggregates. The present study indicated that soil organic C accumulation mainly rely on macro-aggregates (> 250 μm). Intra–particulate organic carbon (POC) and mineral-associated organic carbon (MOC) within macro-aggregates played an important role in soil organic C accumulation. Meanwhile, soil microbes were a driving force for the accumulation of soil organic C physical fractions (POC and MOC). We concluded that OM treatment accelerated the synergistic process between organic C sequestration and soil aggregation, and showed great potential to increase soil organic C accumulation.

Matéria orgânica do solo em agregados biogênicos, intermediários e fisiogênicos sob manejo agroecológico

ABSTRACT Agroecological management can favor the improvement of soil attributes, especially soil organic matter (SOM) and soil aggregation. The objective of the study was to quantify the carbon contents of the humic and oxidizable fractions of SOM of aggregates from different origins from agroecological management systems. Five experimental areas located in the Integrated Agroecological Production System were evaluated: AFS – Agroforestry System; C-SUN – Coffee in full sun; C-SHA – Shaded coffee; AL-FLE – Cultivation in alleys of Flemingia macrophylla with green beans; and NT – No-tillage. The aggregates were separated, identified, and classified as to their origin or formation pathways into biogenic, intermediate, and physicogenic. The carbon contents of the humic fractions fulvic acid (C-FAF), humic acid (C-HAF) and humin (C-HUMF); and oxidizable fractions (F1 and F2, labile; and F3 and F4, recalcitrant) of SOM were determined. The greatest variations in the carbon values of the humic fractions were observed in the aggregates of the AFS, C-SUN and C-SHA systems. In relation to C-HUMF, the highest contents of this fraction were quantified in the biogenic and intermediate aggregates of the C-SUN, C-SHA and AL-FLE systems. The carbon contents of the oxidizable fractions of SOM showed variability between the management systems, mainly for the F1, F2 and F3 fractions in the aggregates under C-SUN and C-SHA. The C-SUN system showed a higher proportion of more humified and recalcitrant fractions of SOM when compared to the C-SHA system. The management practices maids in the agroecological systems of C-SHA, C-SUN and AFS promoted improvements in soil quality.

Long term influence of alternative corn cropping practices and corn-hay rotations on soil health, yields and forage quality

Modifications to continuous corn production systems can reduce environmental impacts and soil degradation, yet the social viability of these modifications is linked to the degree to which they also influence yields and crop quality. In this study, we focus on forage production systems and evaluate how yields, crop quality, soil health indicators, and associated ecosystem services are influenced by corn-hay rotation treatments, cover cropping, and tillage reduction in silage production using a unique 10-year dataset from Borderview Research Farm in Vermont, United States. Physical, chemical, and biological soil health indicators were monitored annually alongside yields and crop quality in a randomized complete block design experiment. We use a mixed model analysis of variance approach to demonstrate significant influences of time and treatments on yields, crop quality and soil health parameters (at p &amp;lt; 0.05). The winter rye cover crop treatment had no significant influence in this study. No-till significantly increased aggregate stability and had no significant effect on other metrics. When cover crop and no-till were combined, they significantly increased soil organic matter content, respiration and aggregate stability. The cover crop, no-till, and no-till cover crop combination treatments had no significant effect on yields or forage quality, suggesting these conservation practices can be adopted without sacrificing yields. Our study also found that corn-hay rotations can significantly increase soil organic matter, respiration, aggregate stability, and crude protein content compared to continuous corn, but they can negatively influence active carbon, total dry matter yield and digestibility. The length of rotation influences the degree to which corn-hay rotations maintain or reduce yields when compared to continuous corn. Shorter rotations of perennial forages (4 years of hay, 6 years of corn) can sustain dry matter yields that are not significantly different from continuous corn, but longer perennial forage rotations (8 years of hay, 2 years of corn) will significantly reduce overall dry matter yields. Among the treatments, no-till in combination with cover cropping in corn silage fields, and a rotation of 4 years of hay to 6 years of corn are likely to achieve the greatest overall benefits in forage production systems.

Ten years of green manuring and biofumigation alters soil characteristics and microbiota

Green manure and biofumigant crops are common within cropping rotations. These practices aim to maintain or increase the yield of agricultural soils by preventing degradation and protecting important ecosystem services, and their benefits to organic carbon levels, soil aggregation, erosion prevention and overall soil fertility are well documented. However, most studies have only examined the short term (one to three year) impacts of green manures and biofumigants, and information on their long term effects is lacking.This study examines the effects of 10 to 13 years of continuous ryegrass (Lolium multiflorum, var. Tetila) green manuring and brassica biofumigation (Brassica juncea, var. Caliente 199) on the soil's chemical, physical characteristics, microbial communities and resulting yields of a fertile, clay rich soil (Red Ferrosol) within an intensive vegetable cropping rotation. The aim was to assess the treatments' efficacy for improving or altering the forementioned parameters to improve sustainable yields, and to examine how the treatments affected the soil's microbial ecology. Soil aggregate stability was assessed at cash crop maturity, and soil chemistry, soil microbiota, and vegetable yields were sampled after the cash crop harvest for three consecutive years. To determine how the soil microbial communities had changed in response to the treatments soil DNA extracts were analysed by high throughput amplicon sequencing.Ryegrass green manuring and brassica biofumigation both altered the soil microbial communities and appeared to favour copiotrophic, organic matter degrading bacteria and fungi. Both treatments increased the relative abundance of arbuscular mycorrhizal fungi (AMF) by 800 % to 1400 % relative to the fallow in two of the three years. Soil aggregate stability was consistently higher in the ryegrass and biofumigant plots and a 20.4 % increase in soil carbon was observed in the treated plots on one side of the trial site. A 20 % increase in cash crop yield (carrots) was recorded in one of the three years.

Modeling Excited States of Molecular Organic Aggregates for Optoelectronics.

Light-driven phenomena in organic molecular aggregates underpin several mechanisms relevant to optoelectronic applications. Modeling these processes is essential for aiding the design of new materials and optimizing optoelectronic devices. In this review, we cover the use of different atomistic models, excited-state dynamics, and transport approaches for understanding light-activated phenomena in molecular aggregates, including radiative and nonradiative decay pathways. We consider both intra- and intermolecular mechanisms and focus on the role of conical intersections as facilitators of internal conversion. We explore the use of the exciton models for Frenkel and charge transfer states and the electronic structure methods and algorithms commonly applied for excited-state dynamics. Throughout the review, we analyze the approximations employed for the simulation of internal conversion, intersystem crossing, and reverse intersystem crossing rates and analyze the molecular processes behind single fission, triplet-triplet annihilation, Dexter energy transfer, and Förster energy transfer.

Soil organic carbon, aggregation and fungi community after 44years of no-till and cropping systems in the Central Great Plains, USA.

Implementing sustainable agricultural land management practices such as no-till (NT) and diversified crops are important for maintaining soil health properties. This study focuses on the soil health of three long-term (44years) tillage systems, NT, reduced tillage (RT), and conventional tillage (CT), in monoculture winter wheat-fallow (W-F) (Triticum aestivum L.) and wheat-soybean (W-S) (Glycine max (L.) Merrill) rotation. Soil organic carbon (C) was higher in NT than CT in the surface 0-5cm, but not different in the 5-15cm, demonstrating SOC stratification on the soil profile. The soil water content was higher in NT followed by RT and CT in the top 0-5cm. We found an association between increased carbon, aggregation, and AMF biomass. Greater soil aggregation, carbon and AMF were observed in NT at 0-5cm soil depth. The W-S cropping system had greater soil microbial community composition based on fungi biomass, AMF and fungal to bacteria ratio from phospholipid fatty acid analysis (PLFA). Large macroaggregates were positively correlated with total C and N, microbial biomass, Gram + , and AMF. Soil water content was positively correlated with macroaggregates, total C and N, and AC. No-till increased soil carbon content even after 44years of cultivation. By implementing conservation tillage systems and diversified crop rotation, soil quality can be improved through greater soil organic C, water content, greater soil structure, and higher AMF biomass than CT practice in the Central Great Plains.

Biochar application increases maize yield under film mulching due to higher soil organic content and soil aggregate stability in a semi-arid area

Biochar application increases maize yield under film mulching due to higher soil organic content and soil aggregate stability in a semi-arid area

IMPROVEMENT OF THE HYDRAULIC PROPERTIES OF SALINE-SODIC SOIL EXPOSED TO FREEZING-THAWING USING SEWAGE SLUDGE AND WETTING-DRYING PROCESS WITH WASTEWATER

Soil improvement practices are needed to protect weakly aggregated saline-sodic soils in cold regions from the negative effects of freezing-thawing events. Amelioration of these soils by adding sewage sludge and applying wetting–drying process with wastewater can be a practical application due to aggregation to be increased with increase in organic matter. Therefore, a laboratory experiment has been conducted to determine the effects on soil properties with three stabilized sewage sludge doses (0, 50, 100 Mg ha−1), two freeze-thaw cycles (5 and 10 times), two wetting-drying intervals (4 and 8 days) and two water types (freshwater and recycled wastewater). The negative effects of freezing-thawing on organic matter and aggregate stability were determined. However, while sewage sludge increased organic matter, aggregate stability, salinity, exchangeable K and Ca+Mg contents, cation exchange capacity (CEC), it was instrumental in inducing a lower pH, exchangeable Na, CaCO3 and exchangeable sodium percentage (ESP), and thus improved field capacity and hydraulic conductivity. Wetting-drying with 8-day intervals and wastewater improved organic matter also. Therefore, it could be concluded that the improvement of hydraulic properties can be attributed to achieving better aggregate stability with increased organic matter in soil from sewage sludge. Long intervals of wetting-drying and recycled wastewater can promote good results as well. However, improving the findings with the proposed treatments in the outer field conditions of the regions exposed to freezing-thawing events will provide more practical use.

Soil organic carbon transfer in aggregates subjected to afforestation in karst region as indicated by 13C natural abundance

The measurement of 13C natural abundance provides valuable information in studying carbon (C) incorporation in soil aggregates. Exploring the pathways of C between aggregates of different size classes are vital to further understand the stabilization of soil organic matter (SOM) and aggregate formation. However, little is known on the mechanism of C stabilization in soil, especially when subjected to afforestation effects in karst rocky desertification area. Soil in the 0–20 cm layer was collected from two afforestation types [natural secondary forest (NF) and artificial Zanthoxylum bungeanum forest (AF)] in the karst rocky desertification area, with cropland (CL) as the reference. Stable isotope fractionation was used to analyze the dynamic changes in organic carbon (OC) in aggregates, and the Δ13C (difference in δ13C between the bulk soil and aggregate fractions) was utilized to quantify the C flow in aggregates under different land use types and soil layers. Results showed that afforestation significantly affected the dynamics of soil aggregate OC. Afforestation on cropland increased the number of large macroaggregates (>2 mm, LMA) and decreased the proportions of small macroaggregates (0.25–2 mm, SMA), microaggregates (0.053–0.25 mm, MI), and silt + clay fraction (<0.053 mm, SC). With the increase in aggregate class size, the OC content in aggregates rose under CL and AF, but no obvious regularity was found in NF. The proportion of new SOC was higher in NF (27.0%) than in AF (20.6%) and in 0–10 cm soil layer (27.3%) than in 10–20 cm soil layer (20.3%) under different afforestation measures. No significant differences in particle size were found among aggregates (P > 0.05). The δ13C in bulk soil and aggregates was significantly decreased by afforestation and increased with the increment in soil depth. Stable isotope analysis results showed that the flow of OC was mainly from larger aggregates to smaller aggregates in CL and AF, which is consistent with the stabilization mechanism of SOM in aggregate hierarchy theory. However, the C flow occurred from smaller aggregates to larger aggregates in NF topsoil due to that newly input OC is first associated with MI and then incorporated into macroaggregates during soil aggregation process. The different human disturbance frequencies and the replenishment levels of plant biomass through litter input, root biomass, and exudates resulted in variation in aggregate turnover (formation and breakdown) among CL, AF and NF. These conclusions can provide sufficient reference for the formation and stabilization of aggregate-associated OC.

Calculation of exciton couplings based on density functional tight-binding coupled to state-interaction state-averaged ensemble-referenced Kohn-Sham approach.

We introduce the combination of the density functional tight binding (DFTB) approach, including onsite correction (OC) and long-range corrected (LC) functional and the state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS or SSR) method with extended active space involving four electrons and four orbitals [LC-OC-DFTB/SSR(4,4)], to investigate exciton couplings in multichromophoric systems, such as organic crystals and molecular aggregates. We employ the LC-OC-DFTB/SSR(4,4) method to calculate the excitonic coupling in anthracene and tetracene. As a result, the LC-OC-DFTB/SSR(4,4) method provides a reliable description of the locally excited (LE) state in a single chromophore and the excitonic couplings between chromophores with reasonable accuracy compared to the experiment and the conventional SSR(4,4) method. In addition, the thermal fluctuation of excitonic couplings from dynamic nuclear motion in an anthracene crystal with LC-OC-DFTB/SSR(4,4) shows a similar fluctuation of excitonic coupling and spectral density with those of first-principle calculations. We conclude that LC-OC-DFTB/SSR(4,4) is capable of providing reasonable features related to LE states, such as Frenkel exciton with efficient computational cost.

METHODS FOR REMOTE QUALITY CONTROL OF COMPOSITES WITH ORGANIC AGGREGATES

The Chinese construction industry has been using the Internet of Things (IoT) to monitor building materials and structures for many years. The achievements of the Chinese construction industry in IoT applications can be used to study and monitor the performance of building materials, including green buildings (energy-efficient building materials).&#x0D; The aim of research: study and optimization methods for remote quality control of composites with organic aggregates.&#x0D; With the help of the developed methods, the following dependencies were obtained: dependences of stresses inside composites with organic aggregates on external influences obtained using a sensor Keyes brick thin film pressure sensor, dependences of deformations inside composites with organic aggregates on external influences obtained using a sensor ultrasonic ranging sensor, dependences of humidity inside composites with organic aggregates on external influences obtained using a sensor Soil moisture sensor, dependences of rheology (cement paste setting time) obtained using a sensor Ph-sensor module.

Variation in shear strength of soil-root system under five typical land use types on the Loess Plateau of China

Shear strength of soil-root system (SRSS) is one of the most useful dynamic properties for evaluating soil erodibility and structural stability. The adjustment of land use may strongly affect SRSS by altering soil properties and plant root system. Few studies have been conducted to investigate the effect of land use on SRSS in semi-arid region. This study was performed to quantify the variation in SRSS with five typical land use types (cropland, orchard, grassland, shrub land and woodland) and identify the related dominant contributing factors on the Loess Plateau where land use has changed greatly in the past several decades. In-situ shear tests with large shear box (25 × 25 × 10 cm) were conducted to measure shear stress-displacement curves. The strain energy calibrated to 15 % soil water content (SEc), peak shear stress (PSS) and the displacement of peak shear stress (DPS) calculated from the curves were used to reflect SRSS. The results showed that woodland had the maximum SEc (124.4 J m−2) and PSS (1048.6 kPa), whereas cropland had the minimum SEc (65.6 J m−2) and DPS (7.2 mm). Woodland, especially coniferous species and its mixed forest, might be the most suitable land use type for vegetation restoration on the Loess Plateau to enhance soil erodibility or structural stability. The variation in SRSS with land use was closely related to the changes in soil properties and root traits. PSS increased with penetration resistance, while it decreased with soil water content. DPS was positive correlated to root biomass and morphological traits. SEc was mainly affected by the direct and indirect effects of root surface area density, penetration resistance, soil organic matter content and aggregate stability. The results are helpful for understanding the mechanical mechanism of vegetation restored soils to mitigate erosion and optimizing land use type in semi-arid region.

Variations in the concentration, composition, and sources of WEOM in erosion and deposition landscapes over an erosion intensity gradient on the Loess Plateau of China

Water-extractable organic matter (WEOM) is the most active and mobile fraction of soil organic matter and responds sensitively to soil erosion. However, previous studies on the chemical nature of WEOM in the erosion and deposition landscapes were controversial at site-level studies and mainly focused on surface soils, limiting our assessment of WEOM’s environmental fate at larger and deeper scales. Here, we collected eroded soils and deposited sediments from a depth of 0–200 cm in five eroding catchments with an erosion intensity gradient across the Loess Plateau. We examined the concentration, composition, and potential sources of WEOM using UV–visible absorption and fluorescence excitation-emission matrix-parallel factor analysis. Soil WEOM quantity and quality varied significantly in the erosion and deposition landscapes, with greater variations in soils below 20 cm, where WEOM in the deposition zone was characterized by higher concentration, aromaticity, hydrophobicity, and UVA and UVC humic-like components derived from terrestrial and soil organic matter. WEOM variations in deep soils increased with increasing erosion modulus among sites, and were mainly driven by changes in soil organic carbon concentration, aggregate stability, and carbon to nitrogen ratio. However, the pattern of WEOM parameters between erosion and deposition zones at 0–20 cm was opposite to that in soils below 20 cm. Vegetation inputs compensated the loss of organic matter in sites with suitable climatic status and weak erosion, and led to higher concentrations and exogenous features of WEOM in the surface erosion area. Concludingly, the WEOM concentration, components, and sources differed significantly between erosion and deposition zones, and these differences, as well as their response to erosion intensity, revealed an opposing pattern in surface and deep soils.

Leymus chinensis resists degraded soil stress by modulating root exudate components to attract beneficial microorganisms.

Phytoremediation is an effective means to improve degraded soil nutrients and soil structure. Here, we investigated the remediation effects of Leymus chinensis on the physicochemical properties and structure of degraded soil after 3 years of cultivation and explored the bacterial and fungal drivers in root exudates by metabolomics and high-throughput sequencing. The results showed that root exudates increased soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP) and soil aggregates, and organic acids in root exudates reduced pH and activated insoluble nutrients into forms that are available to plants, such as available nitrogen (NH4 +-N), nitrate nitrogen (NO3 --N), and available phosphorus (AP). The cultivation of L. chinensis restored the diversity and richness of soil microorganisms and recruited potential beneficial bacteria and fungi to resist degraded soil stress, and L. chinensis also regulated the abundances of organic acids, amino acids and fatty acids in root exudates to remediate degraded soils. Spearman correlation analysis indicated that glutaric acid, 3-hydroxybutyric acid and 4-methylcatechol in root exudates attracted Haliangium, Nitrospira and Mortierella to the rhizosphere and dispersed the relative abundance of the harmful microorganisms Fusicolla and Fusarium. Our results demonstrate that L. chinensis enhances soil fertility, improves soil structure, promotes microbial diversity and abundance, and recruits potentially beneficial microorganisms by modulating root exudate components.

Higher Soil Aggregate Stability in Subtropical Coniferous Plantations Than Natural Forests Due to Microbial and Aggregate Factors

Forest restoration and soil structure stabilization are the focus of forestry and ecology. However, the combined mechanisms of soil microorganisms and organic and inorganic aggregate binding agents on soil aggregation is unclear. In order to explore the effects of subtropical forest restoration types on soil aggregates and the underlying mechanisms, we collected soil samples from subtropical natural forests and coniferous and broad-leaved plantations that are commonly used for forest restoration. The mean weight diameter (MWD) of the soil aggregate was used to indicate the aggregates’ stability. The soil microbial diversity and structure, the organic and inorganic aggregate binding agents including the mycorrhizal density, the glomalin-related soil protein and the Fe and Al oxides were investigated. Results showed that the Shannon and Simpson indices of soil microbial communities in the coniferous plantations were both significantly higher than those in the natural forests. At the annual level, compared with the natural forests, the plantations decreased the proportion of 0.25–1 mm aggregates while the MWD significantly increased. The forest type also significantly affected the mycorrhizal density, the easily extractable glomalin-related soil proteins (EEG) and the Fe oxide. A variance decomposition analysis showed that soil microbial communities, organic and inorganic binding agents, and their interactions together contributed to the aggregates’ composition and stability by 75.07%. The MWD was positively correlated with the microbial diversity, mycorrhizal density and Fe oxide. We therefore suggest that the combined effects of the soil microbial communities and the organic (mycorrhizal density) and inorganic binding agents (Fe oxide) can be the main mechanisms of soil aggregation in the study area, resulting in a higher soil aggregate stability in the subtropical coniferous plantation than in the natural forest.

Nutrient addition affects stability of soil organic matter and aggregate by altering chemical composition and exchangeable cations in desert steppe in northern China

AbstractNitrogen and phosphorus can influence the stability of soil organic matter (SOM) and aggregate, which are important for ecosystem functions. However, understanding remains limited regarding the impact of nutrient addition on soil aggregate stability, aggregate‐relevant organic matter and nutrients in desert steppe. Here, we studied the variation of soil aggregate stability, nutrients, and the exchangeable cations distribution characteristics, and the chemical composition and thermal stability of SOM were analyzed using thermogravimetric (TG) and Fourier transformed infrared spectroscopy. Samples of soil were collected under four conditions, phosphorus addition (P), nitrogen addition (N), combined phosphorus and nitrogen addition (NP), and no addition (CK), from 0 to 10 cm depth over 4‐year experiments in desert steppe in northern China. The percentage of micro‐aggregates (0.25–0.053 mm) and large macroaggregates (&gt;2 mm) dramatically increased by 34.2% and 18.1%, respectively, under the N treatment condition compared to the CK treatment, and micro‐aggregate content significantly increased under the P treatment, respectively. Nitrogen addition significantly increased the soil aggregate stability index, but the P addition reduced their value. The both macro‐aggregates (&gt;0.25 mm) and silt‐clay (&lt;0.053 mm) were preferentially enriched with soil nutrients and the exchangeable cations. The N and P addition was beneficial to nutrients accumulating in macro‐aggregates, and enhanced the aliphatic‐C and aromatic‐C abundances respectively. The TG‐T50 value (i.e., temperature when 50% of SOM is lost) increased after nutrient addition, indicating that the SOM has higher thermal stability, especially in the micro‐aggregates. The addition of N may have potentially a greater influence on aggregate stability through their influence exchangeable polyvalent cations (Ca2+ and Mg2+), and stability of SOM was influenced by chemical composition and exchangeable K+, Na+, Ca2+ contents in desert steppe. Overall, nutrient addition effects stability of SOM and aggregate by altering chemical composition and exchangeable cations in desert steppe in northern China.