Organic Matter Fractions Research Articles

MIGRATION OF HEAVY METALS FROM MINE WASTE ROCK DUMP END ENVIRONMENTAL IMPACT ON GROUNDWATERS AND SEDIMENTS

The environmental impact of mine waste rock dump, located in the region of Srednogorie, Bulgaria on groundwaters and sediments was studied. The acid mine drainage with low pH (2.43 - 3.53), high electrical conductivity (1500 - 4400 μS cm-1), content of Fe, Mn, Cu, Zn, Al, As and high concentration of sulfates (540 - 6905 mg L-1) are formed after heavy rainfall. The content of heavy metals, except manganese, in groundwater was significantly lower than that in the acid mine drainage, and the pH was in the range of 5.43 to 6.62. Sediments in the non-consequential vicinity of the mine waste rock dump had a pH in the range of 2.86 - 4.53 and contained heavy metals and As at concentrations higher than those in the mineral waste due to precipitation, co-precipitation and sorption reactions. An increase in the copper and zinc content in the exchangeable and organic matter fractions was found in the sediment sample. A relationship was found between arsenic and iron concentration in the sediments, which was mainly due to the retention of arsenic in the Fe and Mn oxides fraction. The concentration of total Mn in the sediments was lower than that in the mining waste due to the high mobility of manganese.

Soil properties are affected by vegetation types in a semi-arid mountain landscape

Soil plays a crucial role in the provision of ecosystem services, particularly in mountain areas that are frequently regarded as delicate and vulnerable systems. The alteration of vegetation cover is known to impact the various fractions of organic matter and other soil properties, subsequently influencing the activities of microbes and enzymes that play a role in nutrient cycling. However, there is not much information available regarding the effect on soil properties in semi-arid mountain landscapes. Here, we studied different soil features under woodland (dominated by Carpinus orientalis Miller.), shrubland (dominated by Berberis integerrima Bunge.) and grassland (dominated by Festuca ovina L., Dactylis glomerata L. and Bromus danthoniae Trin.) in the north of Iran. In the summer, a total of eighteen soil (0–10 cm depth) samples were collected from each vegetation type. In addition, to investigate the dynamics of soil microclimate and biota population, the same number of soil samples were collected in the fall season. Results indicated that woodland had a more fertile soil and a higher biological activity than the other vegetation types. Soil earthworm groups showed higher densities in the fall season, whereas soil biota population and microbial processes were enhanced in the summer season. In addition, the study area presented hot spots of soil fertility and biological activities in woodland compared with shrubland and grassland. As a conclusion, distinct soil properties are influenced by various types of vegetation (particularly woody species in contrast to grass covers). With the aim of increasing soil functioning or rehabilitating degraded areas, natural resource managers are suggested to establish wood covers (trees or shrubs) rather than grasslands, whenever possible.

Characterization of organic pollution in the Dianchi Caohai Lake at the transition between the dry and rainy seasons

Dianchi Caohai Lake is heavily polluted, and a significant increase in chemical oxygen demand (COD) occurs during the transition from the dry season to the rainy season. In order to analyze the cause of COD increase, the compositional characteristics of organic matter were investigated using three-dimensional fluorescence spectroscopy technology. The results showed that the most polluted area was located in the geographic center of the outer Caohai Lake, where COD reached 29 mg/L and was elevated by 52%, and protein-like and humus-like features were evident in the organic matter fractions. By measuring the characteristics of water in Caohai Lake, it was found that the fluorescence indexes were greater than 2.47, the biological index was distributed between 0.67 and 1.06, and the humification index was distributed between 1.81 and 3.12. It indicated that the lake had low humification and showed strong autochthonous source characteristics. The bloom outbreak was one of the main reasons for the elevated COD concentration. This study will provide theoretical support for the control of organic pollution in Dianchi Lake.

Straw return-enhanced soil carbon and nitrogen fractions and nitrogen use efficiency in a maize–rice rotation system

Summary Considering straw resource utilization and air pollution prevention, straw return has been commonly practiced in China. However, the practicability of plenty straw return in an emerging maize–rice rotation and their effects on soil C and N pools have not been extensively investigated. This study has been conducted to examine the effects of straw return on soil nutrients, soil functional C and N fractions, and then to figure out their relationships with yield and N use efficiency. Two treatments of straw return (S2Nck) and without straw return (S0Nck) were compared in 3-year field experiment, and subplots without N application were added in their respective plots in the third year. The results showed that, relative to the control (S0Nck), straw return significantly increased soil mineralized nitrogen (Nmin), available P, and exchange K content by 11.7%, 41.1%, and 17.4% averaged across 3-year experiments, respectively. Straw return substantially increased soil dissolved organic C, microbial biomass C, and microbial biomass N content by 73.0%, 25.2%, and 36.8%, respectively. Furthermore, straw return markedly increased C and N retention in particulate organic matter in microaggregates (iPOM) and mineral associated organic matter within microaggregates (intra-SC), but significantly reduced in free mineral associated organic matter (free-SC) fraction. The structural equation modeling analysis showed that yield and the partial factor productivity of N were positively correlated with labile and slow soil C and N fractions. Consequently, straw incorporation significantly increased grain yields of maize by 14.7% and rice by 15.1%. The annual potential reduction proportion in fertilizer-N induced by straw return was estimated to be 25.7% in the third year. This study suggests that the incorporation of straws is an effective way to enhance soil nutrients and regulate soil C and N pools to improve crop production and has the potential to reduce N fertilizer application under maize–rice rotation in subtropical regions.

Organic matter fractions of soil aggregates under agroecological production systems in the southeast of Brazil

Organic matter fractions of soil aggregates under agroecological production systems in the southeast of Brazil

Mineral solubilizing microorganisms and their combination with plants enhance slope stability by regulating soil aggregate structure.

The stability of exposed slopes is prone to natural disasters, seriously threatening socio-economic and human security. Through years of exploration and research, we proposed an active permanent greening (APG) method based on patented mineral solubilizing microorganisms (MSMs) as an improvement over the traditional greening method. In this study, we selected two MSMs (Bacillus thuringiensis and Gongronella butleri) and a plant species (Lolium perenne L.) set up six treatments (T1, T2, T3, T4, T5, and T6) to investigate the effectiveness of the MSMs and their combinations with the plant species on the soil stability using APG method. We noted that both MSMs and the plant species significantly improved soil aggregate stability and organic matter content. Of all the treatments, the T1 treatment exhibited better results, with soil aggregate stability and organic matter content increased to 45.63% and 137.57%, respectively, compared to the control. Soil stability was significant positively correlated with macroaggregate content and negatively with microaggregates. Using structural equation modeling analysis, we further evaluated the mechanism underpinning the influence of organic matter content and fractions on the content of each graded agglomerates. The analysis showed that the macroaggregate content was influenced by the presence of the plant species, primarily realized by altering the content of organic matter and aromatic and amide compounds in the agglomerates, whereas the microaggregate content was influenced by the addition of MSMs, primarily realized by the content of organic matter and polysaccharide compounds. Overall, we observed that the effect of the co-action of MSMs and the plant species was significantly better than that of using MSMs or the plant species alone. The findings of this study provide reliable data and theoretical support for the development and practical application of the APG method to gradually develop and improve the new greening approach.

Transformation and aging of organic matter during degradation and preservation in marine sediment of the northern South China Sea

Organic matter (OM) preservation in marine sediments is an important sink in the carbon cycle and the isotopic records of the preserved OM provide useful information on the sources, biodegradation, and transformation of organic carbon during early diagenesis. Here, we present radiocarbon data combined with stable carbon isotope measurements of total organic carbon (TOC) and four organic fractions, namely, total lipids, hydrolysable amino acids (THAAs), humic acids (HAs), and acid-base insoluble OM, separated from four sediment cores collected from the South China Sea (SCS), to reveal their sources and transformation. The total lipids, THAAs, HAs and acid-base insoluble OM fractions account for 1.1 ± 0.4%, 3.1 ± 1.6%, 12.7 ± 9.4% and 61.6 ± 10.0% of the TOC (the percentages of organic fraction in TOC), respectively, and the acid-base insoluble OM is the dominant fraction of TOC preserved in the sediments. Distinct differences in both 13C and 14C values are found among these organic fractions. The δ13C values are more depleted in total lipids and HAs (−23.1‰ to −30.2‰) than in THAAs and the acid-base insoluble OM (−15.3‰ to −20.6‰), which indicates that HAs could be polymerized from lipid-like materials. The acid-base insoluble OM has the lowest Δ14C values (−848‰ to −358‰), with the oldest 14C ages (mean of 7330 years before present) compared to total lipids (−574‰ to −253‰, 3860 years), THAAs (−331‰ to −66‰, 1527 years) and HAs (−569‰ to −168‰, 2916 years) in these sediment cores. The δ13C and Δ14C values of THAA in the sediment are similar to those of pore-water dissolved organic carbon (DOC), indicating that THAA is preferentially degraded and converted to DOC. These results reveal that OM derived from marine and terrestrial sources decompose selectively and contribute differently to the organic fractions during early diagenesis and preservation in marine sediment. The very aged acid-base insoluble fraction is likely formed as a complex of the most refractory OM during microbial degradation and alteration of TOC, representing a major mechanism of OM sequestration in marine sediments.

Cover crop benefit bacteria and increase aggregate-associate soil C and N storage

The aim of this study was to analyze the effect of four crop sequences with different aboveground biomass and crop residue biochemical composition on biological soil variables, fractions of soil organic matter, and soil aggregation. The study was carried out in a long-term experiment under no-till, in the Argentinean Pampas (31°51′ S; 60°32′ W), on an Aquic Argiudoll. The treatments were: i) fertilized soybean monocropping (Syf), ii) winter cover crop (CC)/ fertilized soybean (CC/Syf), iii) N-fertilized winter CC/fertilized soybean (CCN/Syf), and iv) N-fertilized winter CC/fertilized soybean in a crop rotation: CCN/Syf - wheat [Triticum aestivum L.] for grain production/soybean - maize [Zea mays L.] (CCN/Syf rot). Wheat was used as winter CC. Crop residues were sampled in four moments, and were separated into different fractions. Furthermore, crop residue quality was analyzed according to Van Soest (Cellulose, Hemicellulose, Lignin, Non- structural carbohydrates), and %C and %N was also determined. In soil samples obtained at 0–5 cm depth, we determined: soil organic C, total N, particulate organic matter C and N, mineral-associated organic matter C and N, C and N stocks in different aggregate-size classes, microbial biomass C and N (MBC and MBN), fungal and bacterial biomass-C (FBC and BBC), and N released after a 7-d anaerobic incubation. From June to November, Syf exhibited slower decomposition of soybean stems and an increase in the non-identifiable residue biomass. Intensified crop sequences (i.e., with CC) increased MBC (∼38%) and BBC (∼115%), but had no effect on FBC. The BBC was positively correlated with Hemicellulose (r = 0.86, P < 0.001), but negatively associated with lignin (r = −0.84, P < 0.001) and the lignin:N ratio (r = − 0.89, P < 0.001) in the crop residue. The C and N stocks in aggregates >2000 μm were 263% and 227% greater in treatments with CC than Syf, respectively, and correlated with improvements in the MBC and MBN (r = 0.87, P < 0.001 and r = 0.88, P < 0.001, respectively), particularly the BBC. Intensification of crop sequences through the incorporation of CC provided crop residues with a higher availability of easily decomposable C compounds. This enhancement stimulated the soil biota responsible for decomposition, particularly bacteria. Our study highlights the importance of increasing cropping intensity and covering the soil with live vegetation, resulting in a healthier soil.

Impact of Diverse Agricultural Land Uses on Soil Organic Matter Fractions: A Comprehensive Evaluation

Organic matter is a crucial component of soil that influences various soil properties and functions, including nutrient cycling, soil structure, water holding capacity and microbial activity. Different agricultural land uses significantly influence the quantity and quality of soil organic matter (SOM) fractions. The primary constituent of SOM is humic substances, also known as humus. These are stable compounds originating from the decomposition of organic matter derived from plants, animals, and microorganisms. The soil humic fraction is categorized into humic acid (HA), fulvic acid (FA) and humin (HN) based on the solubility in acid and alkaline medium. The structural arrangement, chemical constitution and stability of the humic substances in soil are affected by various factors, including climate, parent material, altitude, vegetation and the management practices employed in the area. In this context the present study was proposed to assess the impact of various agricultural land use systems on humic acid, fulvic acid and humin fraction in soils of different agro-ecological units (AEUs) of southern Kerala. The study focused on specific AEUs in southern Kerala, including the southern coastal plain (AEU 1), Onattukara sandy plain (AEU 3), southern laterites (AEU 8), south central laterites (AEU 9) and southern and central foothills (AEU 12). Within each AEU, various agricultural land use categories such as, coconut, rice, rubber and uncultivated land were selected as specific focal points for this investigation. The HA, FA and HN content in soil exhibited varying ranges across different AEUs, ranging from 0.57 to 2.06, 0.73 to 2.33, and 0.62 to 1.59 per cent respectively. Among the various land uses, rubber exhibited significantly higher levels of HA (1.72%), FA (2.01%) and HN (1.44%) compared to coconut, rice and uncultivated land. Among the different organic matter fractions, FA (32.30-36.18 %) contributed more towards SOM than HA (29.40-32.51 %) and HN (26.43-29.25 %).

Effect of long-term land use change on soil organic carbon fractions and functional groups

Soil organic matter (SOM) fractions and functional groups can be used to study the short-term as well as the long-term effects of land use change on soil organic carbon (SOC) dynamics. In this study, soil samples of grassland (native vegetation), planted forest and cropland (both converted from grassland) were collected from three soil pedogenetic horizons of A-horizon, AB-horizon and Bk-horizon in a semiarid area of Northeast China. The amounts of SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MOC) were evaluated. After grassland conversion into planted forest and cropland, the amount of SOC decreased by 5.71 and 13.59%, POC decreased by 17.39 and 34.72%, and MOC decreased by 2.84 and 8.36%. Based on the analysis of MOC composition, the average content of humic extract-C decreased by 2.19% and humin-C decreased by 3.08% for planted forest, meanwhile humic extract-C decreased by 14.14% and humin-C decreased by 6.24% for cropland, compared to grassland. This result suggested that labile SOC fractions were more affected by land use change. Solid-state 13C nuclear magnetic resonance (NMR) spectra of bulk soil showed that native grassland SOC had a higher proportion of alkoxy C but a lower proportion of aromatic C, and the aromaticity was less than that of planted forest and cropland. Our results suggested that although the chemical structure of SOM tend to be stable, SOM fraction levels were not enough to recover. Reasonable grassland management measures should be formulated to prevent the continued conversion of native grassland.

Evaluating the effect of organic matter contained in shale on hydraulic fracturing of infill-well

Organic matter which is scattered uniformly in shale can respond to the applied stress and result in the variation of stress field. However, the effects of organic matter content in organic-rich shale on stress interference have not been well considered during developing infill-wells. A fully coupled numerical model is proposed in this paper to consider the whole flow spectrum of shale gas and investigate the effect of organic matter content on stress variation and fracture propagation in infill-well. Through simulating the production and fracturing process with only one set of code, some conclusions can be drawn that the alteration angle of the maximum horizontal principal stress increases and then decreases with the production time. Furthermore, the shrinkage of organic matter enlarges the alteration angle and the magnitude of the maximum horizontal principal stress. Certainly, the optimal fracturing effect in the infill-wells vary due to the different mass fraction of organic matter. This study not only helps to understand the effect of mass fraction of organic matter on stress variation and fracture propagation, but also provides theoretical support for increasing production from shale gas reservoirs.

In the presence of the other: How glyphosate and peptide molecules alter the dynamics of sorption on goethite

The interactions with soil mineral surfaces are among the factors that determine the mobility and bioavailability of organic contaminants and of nutrients present in dissolved organic matter (DOM) in soil and aquatic environments. While most studies focus on high molar mass organic matter fractions (e.g., humic and fulvic acids), very few studies investigate the impact of DOM constituents in competitive sorption. Here we assess the sorption behavior of a heavily used herbicide (i.e., glyphosate) and a component of DOM (i.e., a peptide) at the water/goethite interface, inclusive of potential glyphosate-peptide interactions. We used in-situ ATR-FTIR (attenuated total reflectance Fourier-transform infrared) spectroscopy to study sorption kinetics and mechanisms of interaction as well as conformational changes to the secondary structure of the peptide. NMR (nuclear magnetic resonance) spectroscopy was used to assess the level of interaction between glyphosate and the peptide and changes to the peptide' secondary structure in solution. For the first time, we illustrate competition for sorption sites results in co-sorption of glyphosate and peptide molecules that affects the extent, kinetics, and mechanism of interaction of each with the surface. In the presence of the peptide, the formation of outer-sphere glyphosate-goethite complexes is favored albeit inner-sphere glyphosate-goethite bonds (i.e., POFe) are still formed. The presence of glyphosate induces secondary structural shifts of the sorbed peptide that maximizes the formation of H-bonds with the goethite surface. However, glyphosate and the peptide do not seem to interact with one another in solution nor at the goethite surface upon sorption. The results of this work highlight potential consequences of competition for sorption sites, for example the transport of organic contaminants and nutrient-rich (i.e., nitrogen) DOM components in relevant environmental systems. Predicting the rate and extent with which organic pollutants are removed from solution by a given solid is also one of the most critical factors for the design of effective sorption systems in engineering applications.

Grazing intensity and nitrogen fertilization timing to increase soil organic carbon stock and nitrogen in integrated crop-livestock systems

ABSTRACT Integrated crop-livestock systems (ICLS) foster synergistic relationships to increase nitrogen (N) cycling and soil organic carbon (SOC) accrual in agricultural setups. This study evaluated how the grazing intensity and N fertilization (rates and timing) affect both SOC and N fractions, and soil organic matter chemical composition in an ICLS managed under no-tillage in an Oxisol, six years after initiation. The ICLS was compared to a nearby pasture (PA) and a native forest (NF). The treatments consisted of two grazing intensities: Low Sward Height (LH) and High Sward Height (HH) were maintained with high and low stocking rates, respectively. The HH varied between 0.20 and 0.60 m, and LH between 0.10 and 0.30 m according to the plant forage species throughout the experiment. Fertilization using 200 kg ha -1 N-urea, not splitting up, was conducted at two timings, either at the winter pasture establishment (autumn), about 35 days after sowing or during the summer cash crop cycle (spring). Total N amount per year, including both phases, pasture and cash crop was the same for all treatments. The SOC and N contents were assessed in soil and particulate organic matter (POM), while carbon (C) and N stocks were specifically determined in the soil. Soil organic matter composition was characterized by FTIR. The combination of HH and N fertilization during the pasture phase increased the content of C from 36.1 to 39.9 ± 0.7 g C kg -1 and of N from 2.7 to 3.2 ± 0.1 g N kg -1 . The SOC stocks varied from 37.3 to 41.1 ± 0.7 Mg C ha -1 , and the N stocks from 2.1 to 3.3 ± 0.1 Mg N ha -1 at 0.0-0.10 m soil layer. The SOC content of the POM and the soil organic matter chemical composition determined by FTIR were mainly affected by the grazing intensity. The HH led to an increased in C content within the POM fraction, reaching values of 51.6 ± 1 and 49.2 g C kg -1 , respectively to N crop fertilization and N pasture fertilization. Land-use changed how organic functional groups were stored in soil organic matter fractions. The NF had a greater abundance of aliphatic and phenol in the MAOM, while pasture and ICLS systems had greater aliphatic in the POM fraction. In ICLS, SOC accrual was positively associated with more recalcitrant organic functional groups of phenol, aromatic, and carbonyl C-O. The HH increases SOC accrual, while N-fertilization on pasture ensures adequate nutrition of plants and animals during the winter ICLS phase, at the same time as providing greater residual N for subsequent cash crops through enhanced catalyzed by ruminants. Therefore, grazing and fertilization management strategies should be considered to promote sustainable agriculture intensification with ICLS.

Competition between Dissolved Organic Matter and Freshwater Plankton Control Methylmercury Isotope Fractionation during Uptake and Photochemical Demethylation.

Isotope fractionation related to photochemical reactions and planktonic uptake at the base of the food web is a major uncertainty in the biological application of mercury (Hg) stable isotopes. In freshwater systems, it is unclear how competitive interactions among methylmercury (MeHg), dissolved organic matter (DOM), and phytoplankton govern the magnitude of mass-dependent and mass-independent fractionation. This study investigated how DOM alters rates of planktonic MeHg uptake and photodegradation and corresponding Hg isotope fractionation in the presence of freshwater phytoplankton species, Raphidocelis subcapitata. Outdoor sunlight exposure experiments utilizing R. subcapitata were performed in the presence of different DOM samples using environmentally relevant ratios of MeHg-DOM thiol groups. The extent of Δ199Hg in phytoplankton incubations (2.99‰ St. Louis River HPOA, 1.88‰ Lake Erie HPOA) was lower compared to paired abiotic control experiments (4.29 and 2.86‰, respectively) after ∼30 h of irradiation, resulting from cell shading or other limiting factors reducing the extent of photodemethylation. Although the Δ199Hg/Δ201Hg ratio was uniform across experiments (∼1.4), Δ199Hg/δ202Hg slopes varied dramatically (from -0.96 to 15.4) across incubations with R. subcapitata and DOM. In addition, no evidence of Hg isotope fractionation was observed within R. subcapitata cells. This study provides a refined examination of Hg isotope fractionation markers for key processes occurring in the lower food web prior to bioaccumulation, critical for accurately accounting for the photochemical processing of Hg isotopes across a wide spectrum of freshwater systems.

Spatial–temporal distribution characteristics and traceability analysis of organic matter in Shahe Reservoir (Beijing, China)

Shahe Reservoir is a key node in the upstream of the North Canal, and the water quality has gradually improved after the implementation of low water operation in 2018. The organic matter(OM) in the sediment decreased from 16.66 to 14.22%.In this study, the FI index and parallel factor method were used to investigate the traceability of OM and dissolved organic matter (DOM) in the Shahe Reservoir before and during low water level operation(LWLO), and the results showed that the terrestrial source fraction of OM in sediments was mainly related to organic-rich terrestrial plant residues carried by tributaries and overflows/outfalls during the rainy season, and the FI index indicated that the organic matter (OM) in the Shahe Reservoir before and during LWLO in each DOM in the area is derived from authigenic sources of autotrophic microorganisms, algae, etc. The parallel factor method shows that more than most of the pollutants in the DOM are input from endogenous sources and a small proportion of pollutants are input from exogenous sources. Nutrients in both sediment and interstitial water increased during the LWLO, with TN and TP levels increasing by 262.38 and 204.45 mg·kg−1 in sediment, NH4+–N, PO43−−P, TN and TP in interstitial water increasing by 0.98, 1.36, 2.07 and 4.33 mg·L−1, respectively. Pearson correlation analysis and principal component analysis showed that OM was significantly correlated with nutrients: OM and TN (p < 0.01) and OM and TP (p < 0.05) in the pre-LWLO; OM and TN and TP (p < 0.01) in the LWLO.The results suggested that organic matter pollution control should be mainly carried out from the perspective of endogenous input, focusing on controlling the release of nutrients in sediments.

Comparative Study of Soil Properties and Organic Matter Fractions in Organic and Conventional Farms of Kerala, India

Aims: Assessing various soil properties as influenced by organic farming in the selected certified organic and conventional farms of Kerala.&#x0D; Study Design: Ten pairs of certified organic farms and nearby conventional farms were identified from different agroecological zones of Kerala and were analysed for physical, chemical and biological properties.&#x0D; Place and Duration of Study: The research was conducted at College of Agriculture Vellayani, between December 2020 – June 2021.&#x0D; Methodology: Soil samples were collected from these farms and analyzed for soil physical, chemical and biological properties, organic carbon, total nitrogen, C: N ratio and organic matter fractions.&#x0D; Results: Organic farms exhibited lower bulk density (1.15 Mg m-3) and higher values in porosity (41.32%), water holding capacity (52.68%), mean weight diameter (1.87%), and water stable aggregates (73.59%) compared to conventional farms. Additionally, organic farms were found to be higher in electrical conductivity (0.09 dS m-1), cation exchange capacity (5.98 C mol(p+) kg-1), total organic carbon (7.59%), total nitrogen (0.46%), and C:N ratio (16.14) in comparison to conventional farms. The concentrations of fulvic acid, humic acid, and humin are also greater in organic farms, with mean values of 5.45%, 3.56%, and 0.47%, respectively.&#x0D; Conclusion: Organic farming has a significant role in improving the physical, chemical and biological properties of the soil and also total carbon, total nitrogen and the organic matter fractions.

Soil fertility in silvopastoral systems integrating tree legumes with signalgrass (Urochloa decumbens Stapf. R. Webster)

Silvopastoral Systems (SPS) can increase overall productivity and generate continuous income in order to stimulate simultaneous growth and development of trees, forage and livestock. Moreover, the SPS with tree legumes would be important for add nutrients to the system, mainly N, and ensure the soil health and quality. Soil properties were assessed in two SPS, implanted in 2011, using tree legumes and Urochloa decumbens Stapf. R. Webster (Signalgrass). Treatments were Signalgrass + Mimosa caesalpiniifolia Benth (Sabia) and Signalgrass + Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricidia), and they were allocated in a randomized complete block design, with three replications. Soil was sampled in 2013, 2017, and 2018, at 0, 4, and 8 m along transects perpendicular to tree double rows, from 0- to 20- and 20- to 40-cm layers. Soil chemical properties included pH, P, K+, Ca2+, Mg2+, Al3+, H++Al3+, cation exchange capacity (CEC), and base saturation. In addition, light fraction of soil organic matter (LF-SOM), soil basal respiration (SBR), and natural abundance of 13C of the respired CO2 (δ13C-CO2) were analyzed. Soil pH (5.3, 5.2, 5.1), P (11.3, 7.2, 3.6 mg dm-3), and CECeffective (5.8, 5.1, 5.0 cmolc dm-3) decreased (P &lt; 0.05) along the years 2013, 2017, and 2018, respectively. In 2018, the LF-SOM and δ13C-CO2 was greater in Sabia (1.1 g kg-1 and -16.4‰) compared to Gliricidia (0.7 g kg-1 and -18.2‰). Silvopastoral systems reduced soil fertility regardless of the tree legume species used as result of biomass nutrient stock, without maintenance fertilization. Sabia had greater deposition of LF-SOM, without increasing SBR, providing potential for microbial C use efficiency. Enriched C-CO2 isotope composition shows an efficient SOM oxidize in SPS with Gliricidia or Sabia. This information can contribute to the assessments related to CO2 balance and C retention. Both SPS contribute to C sequestration.

Carbohydrates and carbohydrate degradation gene abundance and transcription in Atlantic waters of the Arctic

Carbohydrates are chemically and structurally diverse, represent a substantial fraction of marine organic matter and are key substrates for heterotrophic microbes. Studies on carbohydrate utilisation by marine microbes have been centred on phytoplankton blooms in temperate regions, while far less is known from high-latitude waters and during later seasonal stages. Here, we combine glycan microarrays and analytical chromatography with metagenomics and metatranscriptomics to show the spatial heterogeneity in glycan distribution and potential carbohydrate utilisation by microbes in Atlantic waters of the Arctic. The composition and abundance of monomers and glycan structures in POM varied with location and depth. Complex fucose-containing sulfated polysaccharides, known to accumulate in the ocean, were consistently detected, while the more labile β-1,3-glucan exhibited a patchy distribution. Through ‘omics analysis, we identify variations in the abundance and transcription of carbohydrate degradation-related genes across samples at the community and population level. The populations contributing the most to transcription were taxonomically related to those known as primary responders and key carbohydrate degraders in temperate ecosystems, such as NS4 Marine Group and Formosa. The unique transcription profiles for these populations suggest distinct substrate utilisation potentials, with predicted glycan targets corresponding to those structurally identified in POM from the same sampling sites. By combining cutting-edge technologies and protocols, we provide insights into the carbohydrate component of the carbon cycle in the Arctic during late summer and present a high-quality dataset that will be of great value for future comparative analyses.

Slope position controls prescribed fire effects on soil: a case study in the high-elevation grassland of Itatiaia National Park

ABSTRACT There is a need for greater knowledge about the medium- and long-term effects of prescribed fire management on soil in ecosystems prone to wildfires and more vulnerable to climate change. This study examined the short- and medium-term effects of prescribed fire on soil chemical properties and chemical fractions of soil organic matter (SOM) in two positions of the landscape in a high-elevation grassland environment. The ecosystem is located in the mountain peaks of southeastern Brazil associated with the Atlantic Forest biome. Prescribed fire was conducted in 2017 to reduce understory vegetation and thus prevent potential severe wildfires. Soil samples were collected at the layers of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m, at eight composite sampling. The composite samples were collected on five different occasions: before the prescribed fire, and 10, 30, 90, and 240 days after the prescribed fire. Soil chemical properties, total organic carbon, labile C, and chemical fractionation of SOM were analyzed. All soil properties investigated were affected by the prescribed fire, with variations in landscape position, duration of effect, and soil layer. In the backslope area, the medium-term effect of fire was negative and induced soil degradation and induced soil degradation. In the footslope area, the system showed greater resilience to the effects of fire, as indicated by the recovery of the soil’s chemical properties. These results can help assess the suitability of controlled burning of vegetation for managing risks of fire in mountainous regions, such as high-elevation grasslands.

Nutrient and Rumen Fermentation Studies of Indian Pasture Legumes for Sustainable Animal Feed Utilisation in Semiarid Areas

This study evaluated 5 annual and 11 perennial Indian pasture legumes species for their nutritive value, dry matter and mineral contents and in vitro fermentation parameters. Legume species differed significantly (p &lt; 0.05) in various nutritional aspects such as organic matter, crude protein (CP), ether extract, fibres and protein fractions. Perennial Clitoria ternateaa had higher (p &lt; 0.05) buffer soluble protein (477), while neutral detergent soluble protein was highest in annually grown Lablab purpureus (420 g/kg CP). Atylosia scarabaeoides (AS) had higher levels of nonstructural carbohydrates (NSCs) (392 g/kg dry matter (DM)) than structural carbohydrates (SC) (367 g/kg DM). Its rapidly degradable fraction (51.7 g/kg (total carbohydrate) tCHO) was lower (p &lt; 0.05) than other fractions of carbohydrates. Total digestible nutrients, digestible energy and metabolisable energy varied, with Desmodium virgatus (DV) having higher values and Stylosanthas seabrana (SSe) having the lowest. Predicted dry matter intake, digestible dry matter and relative feed value also showed significant differences (p &lt; 0.05). Annual grasses such as Dolichos biflorus, Macroptilium atropurpureum, Rhynchosia minima (RM) were found to be better balanced with micro minerals. In vitro dry matter degradability, partition factor, short-chain fatty acids and microbial protein production of legumes varied significantly (p &lt; 0.05). Gas and CH4 production (mL/g and mL/g (digestible DM) DDM) also varied, with Clitoria ternatea-blue having the highest gas production and C. ternatea -white (CT-w) and AS having lower CH4 production. Methane in total gas was low for DV, RM and CT-w (8.99%, 9.72% and 9.51%). Loss of DE and ME as CH4 varied (p &lt; 0.05) among the legumes. Each legume offers unique benefits, potentially allowing for tailored combinations of annual and perennial legumes to optimize rumen feed efficiency.