Soil Aggregates Research Articles

Aqueous and Colloidal Dynamics in Size-Fractionated Paddy Soil Aggregates with Multiple Metal Contaminants under Redox Alternations.

Soil contamination by multiple metals is a significant concern due to the interlinked mobilization processes. The challenges in comprehending this issue arise from the poorly characterized interaction among different metals and the complexities introduced by spatial and temporal heterogeneity in soil systems. We delved into these complexities by incubating size-fractionated paddy soils under both anaerobic and aerobic conditions, utilizing a combination of techniques for aqueous and colloidal analysis. The contaminated paddy soil predominantly consisted of particles measuring <53, 250-53, and 2000-250 μm, with the <53 μm fractions exhibiting the highest concentrations of multiple metals. Interestingly, despite their higher overall content, the <53 μm fractions released less dissolved metal. Furthermore, glucose enhanced the release of arsenic while simultaneously promoting the sequestration of other metals, such as Pb, Zn, and Cu. Utilizing asymmetric flow field-flow fractionation, we unveiled the presence of both fine (0.3-130 kDa) and large (130-450 nm) colloidal pools, each carrying various metals with different affinities for iron minerals and organic matter. Our results highlighted the pivotal role of the <53 μm fraction as a significant reservoir for multiple metal contaminants in paddy soils, in which the colloidal metals were mainly associated with organic matter. These findings illuminated the size-resolved dynamics of soil metal cycling and provided insights for developing remediation strategies for metal-contaminated soil ecosystems.

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.

Phosphorus pool distributions and adsorption-desorption characteristics of soil aggregates in cut slopes of a permafrost zone in the Qinghai-Tibetan Plateau

Soil phosphorus (P) has attracted considerable attention from researchers because of its role in the restoration and stabilization processes of cut slopes in permafrost regions. However, the soil P pool distributions and adsorption-desorption characteristics in alpine cut slopes remain unclear. In this context, we examined in this study the P pools in the aggregates of surface cut soil slopes (0‐10 cm) in areas with three permafrost types, including perennially frozen soil (PF), seasonally frozen ground (SFG), and non-frozen soil (NFS) in the Qinghai-Tibet Plateau, China. In addition, we assessed the P adsorption-desorption characteristics and their correlations with the P pools. The results showed the significant effects of the permafrost types on the contents of total P (TP), available P (AP), labile P (LP), moderately labile P (MLP) and stable P (SP). The inorganic P (IP) contents were higher than those of organic P (OP) in the cut soil slopes of the three permafrost types. In addition, H2O-Pi and NaHCO3-Pi accounted for small proportions of IP, while NaHCO3-Po accounted for the smallest proportion of OP. On the other hand, the SP contents in the soil aggregates were generally higher than those of MLP and LP. In fact, the LP contents in the PF, SFG, and NFS were 72.55, 44.68, and 49.42 mg/kg, respectively. The AP contents in the cut soil slopes of the three permafrost types were significantly correlated with the MLP and LP contents. Moreover, the P adsorption-desorption characteristics of the SFG and NFS were closely related to AP and MLP. Compared with the PF and NFS, the SFG exhibited low and high P adsorption and desorption capacities, respectively. The findings of this study provided an important theoretical basis for the restoration of cut slopes in alpine permafrost regions.

Vegetation degradation reduces aggregate associated carbon by reducing both labile and stable carbon fraction in Northeast China

Vegetation changes can affect soil organic carbon (SOC) content and storage by altering the inputs of plant biomass and the catabolism and anabolism of soil microorganisms. However, influence of vegetation degradation on aggregate associated carbon fractions and the contribution of different aggregates to total SOC in bulk soil remains poorly understood. In this study, undisturbed soil samples were collected from three types of grassland in Songnen grassland: an undegraded grassland (LEY, Leymus chinensis), a moderately degraded grassland (CHL, Chloris virgata), and a severely degraded grassland (SUA, Suaeda heteroptera). Three soil aggregates including macroaggregate (> 0.25 mm), microaggregate (0.053–0.25 mm) and silt and clay fraction (< 0.053 mm) were separated using wet sieving. Contents of total SOC, soil labile and stable carbon in bulk soil and different soil aggregates were measured. Compared with LEY, the mean weight diameter and geometric mean diameter under the degraded vegetation communities reduced by 39.42 % and 28.47 %, respectively. The reduction in SOC contents in bulk soil, macroaggregate, microaggregate and silt and clay fraction resulting from vegetation degradation was 49.81 %, 26.00 %, 76.17 % and 43.65 %, respectively. Under the degraded vegetation communities, contents of soil labile and stable carbon in bulk soil (45.73 % and 52.61 %, respectively), macroaggregate (17.38 % and 31.61 %, respectively), microaggregate (77.83 % and 74.18 %, respectively), and silt and clay fraction (21.20 % and 53.45 %, respectively) were significantly lower than those under LEY. The contribution of macroaggregate, microaggregate and silt and clay fraction to total SOC was 13.27 %, 23.61 % and 63.12 %, respectively. The contribution of soil aggregates to total SOC following vegetation degradation reduced by 53.63 % for microaggregate, but increased by 47.10 % for silt and clay fraction. These findings collectively indicate that vegetation degradation reduces the aggregate associated carbon content by reducing both labile and stable carbon fraction in Songnen grassland, and sustainable vegetation restoration strategies are need to enhance soil carbon storage in Northeast China.

Temperature sensitivity of soil respiration declines with climate warming in subalpine and alpine grassland soils

AbstractWarming as a climate change phenomenon affects soil organic matter dynamics, especially in high elevation ecosystems. However, our understanding of the controls of soil organic matter mineralization and dynamics remains limited, particularly in alpine (above treeline) and subalpine (below treeline) grassland ecosystems. Here, we investigated how downslope (warming) and upslope (cooling) translocations, in a 5-years reciprocal transplanting experiment, affects soil respiration and its temperature sensitivity (Q10), soil aggregation, and soil organic matter carbon (C) and nitrogen (N) composition (C/N ratio). Downslope translocation of the alpine (2440 m a.s.l.) and subalpine (1850 m a.s.l.) to the lowland site (350 m a.s.l.) resulted in a temperature change during the growing seasons of + 4.4K and + 3.3K, respectively. Warming of alpine soils (+ 4.4K) reduced soil organic carbon (SOC) content by 32%, which was accompanied by a significant decrease of soil macroaggregates. Macroaggregate breakdown induced an increased respiration quotient (qCO2) by 27% following warming of alpine soils. The increase in qCO2 respiration was associated with a significant decrease (from 2.84 ± 0.05 to 2.46 ± 0.05) in Q10, and a change in soil organic matter composition (lower C/N ratios). Cooling did not show the opposite patterns to warming, implying that other mechanisms, such as plant and microbial community shifts and adaptation, were involved. This study highlights the important role of SOC degradability in regulating the temperature response of soil organic matter mineralization. To predict the adverse effect of warming on soil CO2 release and, consequently, its negative feedback on climate change, a comprehensive understanding of the mechanisms of C storage and turnover is needed, especially at high elevations in the Alps that are particularly affected by rising temperatures.

Soil Organic Carbon and Aggregate Associated Changes in Three Subtropical Evergreen Forest Ecosystems of China

Soil Organic Carbon and Aggregate Associated Changes in Three Subtropical Evergreen Forest Ecosystems of China

Biochar affects organic carbon composition and stability in highly acidic tea plantation soil

Biochar amendments are effective in stabilizing soil aggregates and improving soil organic carbon (SOC) content. However, the effects of biochar on highly acidic soil and their relation with soil SOC stability remain understudied. The study aimed to investigate the impact of biochar on changes of aggregate distribution and SOC stability in a highly acidic tea plantation soils over an eight-year period. Soil samples were collected from plots with varying biochar application amounts (0, 2.5 t ha−1, 5 t ha−1, 10 t ha−1, 20 t ha−1 and 40 t ha−1). The content of SOC, iron bound organic carbon (OC-Fe), particulate organic carbon (POC), mineral-associated organic carbon (MAOC) and the functional group composition of SOC was analyzed. The results indicated that in the biochar application treatments, the value of soil pH, SOC, POC and MAOC contents were increased from 3.92 to 4.28, 6.68%–187.02%, 8.31%–66.78% and 13.07%–236.47% respectively, compared with CK, while the content of macro-aggregate (particle size>0.25 mm) and soil aggregates mean weight diameter (MWD) significantly increased with higher biochar application amounts. But dissolved organic carbon (DOC) and OC-Fe content exhibited downward trend, decreased from 2.43% to 6.97% and 4.18%–19.91%. Furthermore, aromatic-C levels increased, with increased biochar application amounts. The integration of biochar not only bolstered soil aggregate stability but also amplified the presence of aromatic-C, thereby enhancing the resilience of organic carbon in highly acidic tea garden soil (BC40 > BC20 > BC5>BC2.5 > BC10 > CK), with increases ranging from 6% to 47%. The principal component analysis and structural equation modeling identified soil pH, TN, SOC, POC, MAOC, R > 0.25 and MWD as key factors of soil organic carbon stability. These findings provide crucial insights into the mechanism underlying biochar's efficiency in fortifying organic carbon stability, particularly in the context of highly acidic soil.

Changes in Physical Fractions within Soil Aggregates Under Nitrogen Reduction and Film Mulching Measures in Dryland Wheat Field

We studied the changes in various physical fractions within aggregates in the arid plateau of southern Shanxi Province, which has great significance for synergistically improving soil fertility and crop productivity in this region. Bulk soil samples were collected from 0-20 cm layers during a 7-year long-term experiment in Hongtong County, Shanxi Province. Wheat grain yields, SOC concentrations, proportions, and OC contents within soil aggregates were analyzed. OC contents included： unprotected coarse particulate organic carbon within macroaggregate （M-cPOC） and fine particulate organic carbon within macroaggregate （M-fPOC）, physically protected intra-aggregate particulate organic carbon within macroaggregate （M-iPOC）, chemically/biochemically protected mineral organic carbon within macroaggregate （M-MOC）, unprotected fine particulate organic carbon within microaggregate （m-fPOC）, physically protected intra-aggregate particulate organic carbon within microaggregate （m-iPOC）, and chemically/biochemically protected mineral organic carbon within microaggregate （m-MOC）. The treatments were ① farmer fertilization （FP）, ② nitrogen reduction monitoring and control fertilization （MF）, ③ nitrogen reduction monitoring and control fertilization plus ridge film and furrow sowing （RF）, and ④ nitrogen reduction monitoring and control fertilization plus flat film hole sowing （RF）. The results showed that compared with that in the FP treatment, MF reduced SOC concentration while maintaining wheat grain yield, RF and FH synergistically improved soil fertility and crop yield, especially for the FH with SOC concentration, and wheat grain yield increased by 8.44% and 48.86%, respectively. MF significantly reduced the content of M-cPOC, RF significantly increased the content of M-iPOC, and FH significantly increased the contents of M-fPOC, M-iPOC, M-MOC, and m-iPOC by 64.00%, 98.39%, 6.16%, and 17.48%, respectively. In addition, combined with redundancy analysis, we found that the M-iPOC fraction played a major role in increasing SOC concentration and wheat grain yield, with a contribution rate of 61.5%. Therefore, the contribution of macroaggregates to soil fertility and crop productivity was higher than that of microaggregates in the arid plateau area of southern Shanxi, and flat film hole sowing could increase the content of M-iPOC, thereby synergistically increasing SOC sequestration and wheat grain yield, which could promote this cultivation technology in the region and even in the country's arid agricultural areas.

Soil erodibility mapping using remote sensing and in situ soil data with random forest model in a mountainous catchment of Indian Himalayas.

Land degradation is accelerating in the Himalayan ecosystem, resulting in the loss of soil nutrients due to severe erosion. Soil erosion presents a significant environmental challenge, resulting in both on-site and off-site consequences, such as reduced soil productivity and siltation in reservoirs. Soil erodibility (K factor), an inherent soil property, determines the susceptibility of soils to erosion. Sampling across hilly and mountainous terrain pose challenges due to its complex landscape. Despite these challenges, it is essential to study K factor variations in different land use/land cover types to comprehend the threat of erosion. Digital soil mapping offers an opportunity to overcome this limitation by providing spatial predictions of soil properties. The objective of our study is to map the spatial distribution of soil erodibility using the Random Forest (RF) model, a machine learning method based on sampled in situ soil data and environmental covariates. We collected 556 surface soil samples from the mountainous catchment (Tehri dam catchment) using the stratified random sampling approach. The model performed satisfactorily in both training (r2 = 0.91; RMSE = 0.00185) and testing (r2 = 0.45; RMSE = 0.00318) phases. Subsequently, we generated a digital map with a resolution of 12.5m to depict the distribution of the K factor. Our analysis revealed that key environmental variables influencing the prediction of the K factor included geology, mean NDVI, and climatic factors. The average K factor value was estimated at 0.0304 and ranging from 0.0251 to 0.0400 t ha h ha-1MJ-1mm-1. A higher K factor was observed in the barren land (0.0344) primarily located in the higher and trans-Himalayan region of seasonally snow-covered areas. These areas typically feature young soils with weak soil formation and unstable soil aggregates. Subsequently cropland/cultivated soils (0.0307) exhibited higher K factor values due to the breakdown of soil aggregates by ploughing activities and exposing carbon to decomposition. The average K factor value of evergreen (0.0294) and deciduous (0.0295) forests were the lowest compared to other land use/land cover types indicating the role of forests in resisting soil erosion. By assessing and predicting soil erodibility, land planners and farmers can implement erosion control measures to protect soil health, prevent sedimentation in water bodies, and sustain agricultural productivity in the Himalayas.

The effects of roots and earthworms on aggregate size distribution and their associated carbon under contrasting soil types and soil moisture conditions

Soil’s potential as a carbon sink is uncertain due to biotic and abiotic interactions. Soil aggregates are important carriers of organic carbon (OC), and clarifying the response of aggregates and their associated OC to plant roots and earthworms can better understand the carbon cycle in terrestrial ecosystems. Herein, we determined the regulatory role of plant roots (Lolium perenne) and earthworms (Metaphire tschiliensis) in isolation and in combination on aggregate size distribution and their associated OC and readily oxidizable OC (ROOC) under contrasting soil types (Phaeozems and Anthrosols) and soil moisture conditions (constant wetting, CW; wetting–drying cycle repeated four times, 4WD) by a laboratory microcosm experiment. Results showed that earthworm presence significantly increased plant biomass by 30 % and 221 % in Phaeozems and Anthrosols, respectively (p < 0.05). For Phaeozems, plant alone (P) and plant and earthworm in combination (PE) had lower proportion of large aggregate (5–8 and 2–5 mm) than bare soil (CK) under 4WD condition (p < 0.05). For Anthrosols, the PE treatment decreased the proportion of 5–8 and 2–5 mm aggregate by 45 % and 25 %, respectively, under CW condition, and decreased the proportion of 5–8 mm aggregate by 37 % under 4WD condition (p < 0.05). Moreover, the proportion of 5–8 and 2–5 mm aggregate in P treatment was lower under CW condition (6.92 % and 22.13 %) but was higher under 4WD condition (11.49 % and 32.55 %) than those in CK (14.69 % and 29.91 %; 8.85 % and 20.56 %) (p < 0.05). Our results further indicated that the PE treatment had relatively higher OC and ROOC contents, especially for small aggregates in Anthrosols. The study indicates that plant roots and earthworms significantly influence aggregate turnover and the carbon cycle, with soil type and moisture playing a crucial role.

Long-term organic fertilization increases phosphorus content but reduces its release in soil aggregates

There is currently limited published information on the coupling correlation between phosphorus (P) redistribution and release in soil aggregates. To fulfill this gap, we conducted a 10-year field experiment of soil amended with organic fertilizer to investigate phosphorus transformation and immobilization during the organic fertilization process. Microbial communities, functional genes and enzymes were analyzed to elucidate the multi-mechanisms of the conversion among phosphorus fractions. Phosphorus content in soil aggregates was determined as follows: FeP (34 % ~ 45 %) > Ca-P (16 % ~ 27 %) > Oc-P (15 % ~ 17 %) > Or-P (13 % ~ 19 %) > Al-P (4 % ~ 5 %) ≈ Ex-P (2 % ~ 4 %). Compared to a control with only chemical fertilizer, a 13 % ~ 38 % increase in P availability of experimental treatments mixed with chemical and organic fertilizers was attributed to the mineralization of Or-P, but not to the dissolution of inorganic P. Following organic fertilization, the phnF gene was dominant factor to promote the mineralization of Or-P, because it encodes CP lyases that pyrolyzes the CP bounds in organophosphate esters. Overall, organic fertilization decreased P release risk in soil aggregates, especially for the micro-aggregates that showed a higher capacity to activate non-available P and immobilize endogenous P in farmland soil. These results provide a theoretical guidance for the source control of P pollution in agro-ecosystems.

Influence of long-term ecological reclamation on carbon and nitrogen cycling in soil aggregates: The role of bacterial community structure and function

Understanding the influence of microbial taxa and functions on soil carbon (C) and nitrogen (N) cycling, particularly concerning soil aggregate sizes, is crucial for ecosystem management. This study examines the taxonomic and functional dynamics of soil bacterial communities within different aggregate sizes over time. Soil samples from a reclamation forest on the Loess Plateau in North China were collected across reclamation ages of 0, 3, 18, and 28 years. Soil aggregates were categorized into large macro-aggregates (>2000 μm), small macro-aggregates (250–2000 μm), and micro-aggregates (<250 μm) using a modified dry-sieving method. Soil aggregate stability, C and N concentrations, newly derived plant C, enzyme activities, bacterial communities, and functional genes in each aggregate fraction were systematically analyzed. There was a notable increase in soil aggregate stability and a higher proportion of large aggregates was found with increasing forest age. There were significant differences in bacterial community structures, particularly between micro-aggregates and large macro-aggregates and across different forest ages. Reclamation led to an increased abundance of copiotrophic bacterial taxa. Decreases in N-acquiring enzyme activity in micro-aggregates were contrasted by an increase in C, N, and phosphorus (P) acquisition activities in larger aggregates over time. Larger aggregates showed a faster recovery of C and N cycling genes accompanied by a significant enhancement in acetyl-CoA and ammonia oxidation processes, underscoring their importance in soil nutrient cycling. These results highlight the critical role of aggregate size in shaping microbial community structures and functions that influence soil C and N cycling during reclamation and provide new perspectives highlighting the significance of incorporating aggregate size considerations into soil management and reclamation strategies.

Does the presence of mineral nutrient enhance the carbon sequestration, soil aggregation, and microbial biomass in the subtropical clay soil?

Crop residue incorporation is considered as a promising approach for improving carbon sequestration coupling with soil aggregation (MWD). However, better understanding is needed regarding to the mechanism of carbon sequestration and aggregation following crop residue return in subtropical clay soil. A short-term field experiment (1.5 years) was conducted to explore the underlaying potential mechanism of carbon sequestration after crop residues return in the subtropical clay soil. Four treatments were applied as follows: (1) Control, (2) Inorganic fertilization (NPK), (3) Crop residue at 8-ton ha−1, (6) NPK + Crop residue at 8-ton ha−1. MWD, soil organic carbon (SOC), microbial biomass carbon (MBC), glomalin protein (GRSP), mineral and aggregate-associated SOC, and Fe oxides were determined. Results exhibited that the mineral nutrients with or without crop residue enhanced the SOC significantly in comparison to the only straw and control treatments (P < 0.05). The short-term residue return enhanced the MWD compared to the baseline soil, which was less than control due to the greater concentration of amorphous Fe oxides. Moreover, GRSP and MBC were significantly increased upon crop residue return in presence of mineral nutrients treatment (P < 0.01). SOC was reduced in the order of NPK > NPK + Crop residue > Crop residue > control, while MBC and GRSP were increased in the order of control < Crop residue < NPK < Crop residue + NPK. Aggregate-associated and mineral-associated SOC of aggregates were enhanced in presence of mineral nutrients (P < 0.001). Our results suggest that the nutrients addition in presence or absence of crop residue return under short-term field experiment is considered as a promising and sustainable clay soil management approach for enhancing carbon sequestration to mitigate climate change.

Vegetation restoration changed the soil aggregate stability and aggregate carbon stabilization pathway according to δ13C signatures

Vegetation restoration can increase soil organic carbon (SOC) sequestration through the physical protection of soil aggregates. However, the soil aggregate stability and C flow pathway associated with long-term plantation restoration have not yet been fully characterized. Here, we conducted a study on Robinia pseudoacacia plantations at different recovery stages, studied the distribution and stability of aggregates, analysed the aggregate-associated organic carbon (OC) content and δ13C value, and quantified the aggregate C flow pathway. The results revealed that vegetation restoration increased the proportion of large macroaggregates (LMAs) and decreased the proportion of small macroaggregates (SMAs), with no changes observed in the proportion of microaggregates (MIAs) or silt + clay (SC) at 0–20 cm. The indices of aggregate stability, namely, the mean weight diameter (MWD), geometric mean diameter (GMD) and structural stability index (SSI), increased under vegetation restoration at 0–20 cm, with maximum values of 3.83 mm, 2.88 mm, and 2.00 %, respectively, at 35 years of age (35Y). The OC content of the LMAs increased from 10.96 to 21.64 g kg−1 and from 7.27 to 10.05 g kg−1 in the 0–20 cm and 20–40 cm layers, respectively. LMAs and SMAs had the greatest contributions to SOC accumulation in the 0–20 cm and 20–40 cm layers, respectively. The δ13C value increased with decreasing aggregate size. The C flow pathway was from macroaggregates to MIAs or SC. Compared with abandoned farmland, vegetation restoration decreased the aggregate C flow intensity in the 0–20 cm layer. The soil aggregate stability and aggregate-associated OC content decreased with increasing soil depth, but the soil δ13C value exhibited the opposite trend. Vegetation restoration regulated soil aggregate stability by influencing the fine root biomass (FRB) and SOC content. In summary, our analysis offers a valuable reference for the controlling effect of aggregation on C stability influenced by vegetation restoration.

Are bacterial communities and aggregation in fragile soils influenced by the management system?

Light-textured soils are widely distributed globally and, despite their limitations, have been integrated into agricultural production systems. This study aimed to assess how management systems—conventional tillage (CT) and no-till (NT)—affect aggregate formation pathways (physicogenic and biogenic) and bacterial communities. Two management systems (NT and CT) and three cover crops were evaluated: CJ: Crotalária (Crotalaria juncea (40 ​kg ​ha−1); M: Millet (Pennisetum glaucum - 60 ​kg ​ha−1); and C: Cocktail (Crotalária - Crotalaria juncea - 10 ​kg ​ha−1, Jack bean - Canavalia ensiformis - 75 ​kg ​ha−1, and Millet - Pennisetum glaucum - 30 ​kg ​ha−1). Undisturbed soil samples were collected from the crop row at a depth of 0.00–0.10 ​m. Aggregates with diameters between 9.7 and 8.0 ​mm were classified as biogenic or physicogenic. In addition to the chemical attributes of the aggregates, total organic carbon (TOC) and its fractions (mineral-associated organic carbon, MAOC; particulate organic carbon, POC; and free light fraction carbon, FLFC) were quantified. The structure and bacterial composition of the aggregates were also characterized. A higher proportion of biogenic aggregates (53–64%) was observed compared to physicogenic aggregates (36–47%). Cover crops exhibited significant differences in pH, calcium (Ca2+), base saturation, phosphorous (P), and percentage of base saturation. The management systems differed significantly for Ca2+ and P, with CT showing higher values than NT. The management system influenced organic matter accumulation and stabilization in the aggregates, with MAOC content being significantly lower in CT. POC and TOC were also significantly lower in physicogenic aggregates under CT. Bacterial community richness, diversity, and structure were significantly influenced by the management system, with greater richness and diversity in NT compared to CT. Network analysis revealed NT had more nodes and edges (65 and 406, respectively) than CT (52 and 357, respectively. Phyla abundance differed between the systems, with Firmicutes and Entotheonellaeota more abundant in CT, while WPS_2, GAL15, Bdellovibrionota, and Myxococcota were more abundant in NT. Despite the relatively short period of NT implementation (5 years), it had a positive effect on the bacterial community, which may subsequently influence nutrient and carbon content and their fractions in the aggregates.

Quantification and mapping of regulating ecosystem services in canola agroecosystems (case study: Gorgan County, Iran).

Regulating services are the advantages that humans receive from regulating ecosystem processes. These services include, but are not limited to pollination, climate regulation, water purification, carbon sequestration, and erosion control. Quantifying and mapping ecosystem services in agroecosystems is one of the main effective actions to increase pay attention to these services and adopt suitable approaches to direct sustainability. The purpose of the study was quantification, and mapping of regulating ecosystem services in canola agroecosystems of Gorgan County, north of Iran. For this purpose, some regulating services such as carbon sequestration, climate regulation, soil microbial respiration, soil aggregate stability, and pollination by insects were evaluated based on the Common International Classification of Ecosystem Services framework. The information and data required for each of these services were collected through field measurements, laboratory experiments, and field surveys. After quantifying, the surveyed services in canola agroecosystems were presented on geospatial maps generated by ArcGIS software, version 10.3. Results showed that agroecosystems in the west and north of the studied region provided the more regulating services. Also, the results of the pollination showed that pollinating insects belonged to four orders and 13 families. The majority of the pollinators were Hymenoptera (44.74%), especially honey bees (Apis mellifera L.), Diptera (5.26%), Butterflies (Lepidoptera; 25%), and the beetles (Coleoptera; 25%), and Anthophora sp. and Andrena sp. were the second and the third most abundant pollinating species after honey bees. Generally, the canola agroecosystems close to the rivers and the natural ecosystems provided more services than other regions.

Land Use affects the Soil Aggregation Pattern during Restoration of Degraded Land under Tropical Dry Climate

Soil aggregate formation and stability are crucial in safeguarding soil carbon pools, as they form the basic unit of soil structure in terrestrial ecosystems. The impact of different land uses on soil aggregation pattern has widely been studied but is limited under tropical dry climate conditions. This study aimed to determine the soil aggregation pattern at two soil depths (0-15 cm and 15-30cm) in three different plantations (Peltophorum pterocarpum, Eucalyptus globulus, and Acacia nilotica) established in degraded land under tropical dry climate. The soil aggregates were categorized into microaggregate, mesoaggregate and macroaggregate based on their size fractions which were determined by the wet sieving method. The percent of macroaggregate, mesoaggregate, and microaggregate fractions at 0-15 cm depth ranged from 62.2 – 82.6%, 31.6 – 36.7%, and 1.1 – 4.9 % respectively whereas at 15-30 cm depth, it ranged from 69.7 - 81.7%, 17.1 - 31.6%, and 1.2 - 2.8%. The mean weight diameter values at 0-15 cm and 15-30 cm soil depth ranged from 2.27-3.37mm and 2.85-3.35 mm respectively. The higher percentage of macroaggregate fractions in Peltophorum pterocarpum plantation compared to Eucalyptus globulus, and Acacia nilotica plantations indicated that the Peltophorum pterocarpum plantation has slightly more potential to improve aggregate formation and soil structure in the degraded lands under tropical dry climate. In addition, appropriate land use practices can increase soil aggregate stability in the study area.

Long‐Term Biochar Application Improved Aggregate K Availability by Affecting Soil Organic Carbon Content and Composition

ABSTRACTStraw biochar is an effective amendment at improving soil aggregate structure and increasing soil carbon and potassium (K) content. However, little information is available on the relationship between soil organic carbon (SOC) and aggregate‐associated K distribution under long‐term biochar application conditions. To address this, a field trial established in 2013 was used to examine the impact of biochar (B0: 0 and B1: 2.625 t ha−1 year−1) and K fertilizer (K0: 0 and K1: 60 kg ha−1 year−1) on the variation in soil aggregate K and reveal the associated influencing factors. A total of four treatments (B0K0, B0K1, B1K0, and B1K1) were included in this study. The soil analysis results obtained in 2021 showed that after 9 years' amendment, B1K1 increased the aggregate exchangeable K (EK) and nonexchangeable K (NEK) pools by 27.40% and 39.55%, respectively, and the increment was primarily because biochar enhanced &gt; 0.25 mm aggregate fractions and strengthened soil K+ adsorption capacity, which benefit from a synergistic increase in SOC and humic acid (HA) content by biochar. 13C NMR analysis showed that long‐term biochar applications altered the chemical composition of SOC, with an outcome of increased aromaticity and hydrophobicity but decreased the lipidation of SOC, indicating that the complexity of SOC molecular structure was enhanced and eventually contributed to strengthening the macroaggregates stability and soil K+ adsorption capacity. The correlation analysis revealed that soil aggregate EK and NEK contents were positively correlated with SOC and HA contents, which further proved that increase of SOC and soil HA is a significant mechanism for biochar ameliorate soil aggregate‐associated K availability.

Long-term Chinese milk vetch incorporation promotes soil aggregate stability by affecting mineralogy and organic carbon

Soil aggregates profoundly impact soil sustainability and crop productivity, and they are influenced by complex interactions between minerals and organics. This study aimed to elucidate the alterations in mineralogy and soil organic carbon (SOC) following long-term green manure incorporation and the effect on soil aggregates. Based on 5- and 36-year field experiments, surface soil samples (0-20 cm) were collected from Alfisol and Ferrisol soils subjected to rice-rice-winter fallow (CK) and rice-rice-Chinese milk vetch (MV) treatments to investigate aggregate stability, mineralogy, SOC composition, and soil microstructural characteristics. The results showed that high clay-content Ferrisol exhibited greater aggregate stability than low clay-content Alfisol. The phyllosilicates in Alfisol primarily comprised illite and vermiculite, whereas those in Ferrisol with high-content free-form Fe oxides (Fed) were dominated by kaolinite. Additionally, the clay fraction in Ferrisol contained more aromatic-C than the clay fraction in Alfisol. The 36-year MV incorporation significantly increased the Ferrisol macroaggregate stability (9.57-13.37%), and it also facilitated the transformation of vermiculite into kaolinite and significantly increased the clay, Fed, and aromatic-C contents in Ferrisol. Backscattered electron (BSE)-scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) revealed a compact aggregate structure in Ferrisol with co-localization of Fe oxides and kaolinite. Moreover, the partial least path model (PLS-PM) revealed that clay content directly improved macroaggregate stability, and that kaolinite and Fed positively and directly affected clay or indirectly modulated clay formation by increasing the aromatic-C levels. Overall, long-term MV incorporation promotes clay aggregation by affecting mineral transformation to produce more kaolinite and Fe oxides and retain aromatic-C, and it ultimately improves aggregate stability..

Reduced ligninase‐cellulase ratio enhances soil carbon sequestration following afforestation of agricultural land

AbstractIntroductionAfforestation of agricultural land is one of the most essential approaches to mitigate climate change by enhancing the sequestration of atmospheric carbon (C) into the soil. C‐degrading extracellular enzymes produced by soil microbes regulated the decomposition and fate of sequestrated soil organic carbon (SOC), with potential divergent variations following afforestation across different ecosystem scales. However, the feedbacks of different C‐degrading enzymes and their relationships with SOC following afforestation of agricultural land remain unclear.Materials and MethodsWe investigated the changes in enzyme activity and their relationships with SOC in soil aggregates across two typical climatic vegetation restoration regions in China, and explored the mechanisms through which changes in enzyme activity contribute to SOC sequestration following afforestation of agricultural land.ResultsAfforestation of agricultural land generally decreased ligninase activity and increased cellulase activity across various aggregate fractions, compared to the adjacent croplands in both subtropic (Danjiangkou Reservoir, DJK) and temperate (Maoershan, MES) region. Additionally, the ratio of ligninase to cellulase (L:C) was lower in afforested lands than in the croplands, with L:C as the major factor explaining the variations of SOC sequestration following afforestation. Specifically, ligninase and L:C were negatively correlated with SOC, whereas cellulase showed positive correlations with SOC. Further analyses suggested that microbial biomass C and nitrogen (MBC and MBN) and the ratio of SOC and total nitrogen (SOC:TN) were important factors influencing L:C and subsequently regulating SOC. These results suggest that shifts in microbial enzyme production from ligninase to cellulase following afforestation, reduced the decomposition of recalcitrant C, thus contributing to SOC sequestration.ConclusionOur work underscores the critical role of reduced L:C in enhancing SOC sequestration following the restoration of croplands to afforested lands. These findings advance the understanding of the influence of microbial community physiological adaptations on C sequestration across different land use types.