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Background and aims: As a significant land carbon sink, highly acid subtropical forests in southern China continued to accumulate a significant amount of soil carbon under elevated acid deposition, yet the mechanism of how soil organic carbon (SOC) and its two components: particulate (POC) and mineral-associated (MAOC) organic carbon increased remain unclear. We aim to assess which mechanism and drivers dominated the accumulation of SOC and its two fractions under elevated acid deposition. Methods: We conducted a 11-year field acid addition experiment to study how acid deposition affected the accumulation of SOC and its fractions. Lignin phenols and amino sugars were used as two tracers for plant- and microbe-derived carbon. Results: We found that both POC (0–20 cm) and MAOC (10–20 cm) were significantly increased by acid addition. Acid addition significantly reduced the contributions of fungal-, bacterial- or total microbial residue carbon to SOC but significantly increased the plant-derived soil carbon in both soil depths. The increase of lignin phenol and suppressed soil organic matter decomposition from soil microbes suggested that soil POC increased with acid addition. Soil acidification strongly enhanced MAOC accumulation through increased lignin and mineral protection by iron-aluminum oxides and cations. Conclusion: Our results showed that increased mineral protection of plant-derived carbon was the dominant driver of the increased SOC sequestration under acid addition. This finding identified the dominant pathway for SOC accumulation in a highly acidic subtropical forest and provides new insights into understanding how plant-soil-mineral interact under increasing acid deposition in the region. [ABSTRACT FROM AUTHOR]

Soil disinfestation has been widely used as an effective strategy to improve soil health and crop yield by suppression of soil-borne plant pathogens, but its effect on soil organic carbon (SOC), a crucial factor linked to climate change, remains unknown. A microcosm trial was conducted to evaluate microbial residue carbon (MRC) and its contribution to SOC under chemical soil disinfestation (CSD) with quicklime (QL) and chloropicrin (CP), as well as anaerobic soil disinfestation (ASD) with maize straw (MASD) and soybean straw (SASD). The SOC concentrations were increased by both CSD and ASD. Also, total SOC-normalized MRC concentration was enhanced, with a considerable increase in soil bacterial and fungal MRC, particularly evident under CP and SASD treatment. Due to broad-spectrum biocidal activities, decreased SOC-normalized microbial biomass carbon (MBC) was consistent with the reductions in bacterial and fungal phospholipid fatty acids (PLFAs), consequently increasing MRC accumulation under CSD. Similarly, ASD decreased fungal PLFAs while shifting bacterial PLFAs from aerobic to anaerobic taxa or from gram-negative to -positive taxa, both of which contributed to both MBC and MRC buildup. Collectively, the findings demonstrate that ASD can efficiently increase SOC concentration, with distinct mechanisms underlying MRC generation when compared to traditional CSD. [ABSTRACT FROM AUTHOR]

Aims: Soil organic carbon (SOC) storage is mainly governed by inputs from plant and microbial sources. How the relative contributions of these two sources in forest soils vary along broad-scale environmental gradients is poorly understood. The contributions of these two carbon sources in different soil layers are also elusive. Methods: We used amino sugar and lignin phenol as biomarkers to indicate microbial- and plant-derived soil carbon. The concentrations of amino sugar and lignin phenol in topsoil (0–10 cm) and subsoil (30–60 cm) of major forest types along a latitude gradient in China were investigated. Results: The concentration of soil amino sugar decreased along the latitude in topsoil, which is mainly controlled by the variations in mean annual temperature and soil nitrogen. The concentration of lignin phenols decreased along latitude in topsoil, mainly controlled by soil carbon/nitrogen ratio. The microbial-derived carbon was mainly composed of fungi-derived in topsoil, while bacteria-derived dominated in subsoil. Climate and soil properties are primary factors controlling the persistence of microbial residues and lignin phenols in topsoil, and soil clay is the crucial factor in the subsoil. Conclusions: Both microbial residuals and lignin phenols in topsoil showed a decreasing trend with increasing latitude, but controlled by different sets of environmental factors. Subsoil microbial residues and lignin phenols showed no trend along the latitude and are mainly influenced by soil clay content.These findings provide new insights on how climate and vegetation affect soil carbon persistence, revealing significant distribution patterns of forest soil microbial residuals and lignin phenols along a latitude gradient. [ABSTRACT FROM AUTHOR]

Microbial-sourced carbon is an important component of soil organic carbon (SOC) and influences SOC's size and turnover. Soil extracellular enzymes can participate in the degradation of plants in the soil to produce substances needed by microorganisms, which in turn affects microbial sources of carbon. Most of the current studies focus on the effects of soil extracellular enzymes on SOC pools, while there is a lack of clarity regarding the effects on microbial sources of carbon during SOC pool formation. In this paper, three typical grassland types (alpine meadow, alpine grassland, and desert grassland, respectively) on the Tibetan Plateau were selected as research objects to investigate the effects of grassland type and soil depth on microbial-sourced carbon (amino sugars) and soil extracellular enzymes (hydrolytic enzymes: β-glucosidase and cellulase; oxidative enzymes: peroxidase and polyphenol oxidase) in the soil profiles. Our study shows that the content of amino sugars in the three grassland types followed the order: alpine meadow > alpine grassland > desert grassland; the content of hydrolytic enzyme followed the order of alpine meadow > alpine grassland > desert grassland; the content of oxidative enzyme followed the order of desert grassland > alpine grassland > alpine meadow; amino sugars content showed a positive correlation with hydrolytic enzymes and a negative correlation with oxidative enzymes; and the hydrolytic enzyme was the main factor promoting the accumulation of amino sugars. The environmental conditions of alpine meadows and alpine grasslands are more favorable for the formation of microbial-derived carbon and have greater sequestration potential, while desert grasslands are not favorable for the formation of microbial-derived carbon. The results of this study provide a reference basis for exploring the model of organic carbon sequestration in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) represents the largest carbon reservoir in terrestrial ecosystems. Therefore, understanding how to enhance SOC is crucial for the global carbon cycle and atmospheric CO2 removal. While there has been reported on SOC accumulation following forest restoration efforts, changes in plant lignin and microbial necromass across soil fractions and depths remain unclear. To address this gap, we investigated the SOC-standardized concentrations of lignin phenols and amino sugars in bulk soil and soil fractions (particulate organic matter (POM) and mineral-associated organic matter (MAOM)) during subtropical forest restoration, as tracers for change in plant lignin components and microbial necromass respectively. Our findings indicate that forest restoration does not affect SOC concentrations, but does result in changes in plant lignin and microbial necromass. Specifically, in the subsoil, lignin phenols and amino sugars concentrations in bulk soil and soil fractions rise significantly with restoration time, with lignin phenols and amino sugars concentrations in bulk soil rising by 29.6% and 53.0%, respectively. This suggests that as forests recover, lignin and microbial necromass have a higher contribution to SOC accumulation in the subsoil, while the contribution of low-molecular plant-derived organic matter decreases. The relative change rate of lignin phenols (relative to SOC) is greater than that of amino sugars in POM in the topsoil, while in the subsoil, the relative change rate of amino sugars in MAOM is greater than that of lignin phenols. These results indicate that lignin in POM declines more rapidly than amino sugars during restoration, whereas in MAOM, amino sugars accumulate faster than lignin. Overall, these findings provide important insights into the regulation of SOC accumulation during forest restoration by the combination of plant lignin and microbial necromass in various stabilization pathways.

Soil disinfestation has been widely used as an effective strategy to improve soil health and crop yield by suppression of soil-borne plant pathogens, but its effect on soil organic carbon (SOC), a crucial factor linked to climate change, remains unknown. A microcosm trial was conducted to evaluate microbial residue carbon (MRC) and its contribution to SOC under chemical soil disinfestation (CSD) with quicklime (QL) and chloropicrin (CP), as well as anaerobic soil disinfestation (ASD) with maize straw (MASD) and soybean straw (SASD). The SOC concentrations were increased by both CSD and ASD. Also, total SOC-normalized MRC concentration was enhanced, with a considerable increase in soil bacterial and fungal MRC, particularly evident under CP and SASD treatment. Due to broad-spectrum biocidal activities, decreased SOC-normalized microbial biomass carbon (MBC) was consistent with the reductions in bacterial and fungal phospholipid fatty acids (PLFAs), consequently increasing MRC accumulation under CSD. Similarly, ASD decreased fungal PLFAs while shifting bacterial PLFAs from aerobic to anaerobic taxa or from gram-negative to -positive taxa, both of which contributed to both MBC and MRC buildup. Collectively, the findings demonstrate that ASD can efficiently increase SOC concentration, with distinct mechanisms underlying MRC generation when compared to traditional CSD.

Abstract Background Microbial residues are significant contributors to stable soil organic carbon (SOC). Soil aggregates effectively protect microbial residues against decomposition; thus, microbial residue accumulation and distribution among soil aggregates determine long-term SOC stability. However, how tree species influence accumulation and distribution of soil microbial residues remains largely unknown, hindering the chances to develop policies for SOC management. Here, we investigated microbial residue accumulation and distribution in soil aggregates under four subtropical tree species (Cunninghamia lanceolata, Pinus massoniana, Michelia macclurei, and Schima superba) after 29 years of afforestation. Results Accumulation of microbial residues in the 0–10 cm soil layer was 13.8–26.7% higher under S. superba than that under the other tree species. A structural equation model revealed that tree species affected the accumulation of microbial residues directly by altering fungal biomass. Additionally, tree species significantly affected microbial residue distribution and contribution to SOC in the top 20 cm soil. In particular, microbial residue distribution was 17.2–33.4% lower in large macro-aggregates (LMA) but 60.1–140.7% higher in micro-aggregates (MA) under S. superba than that under the other species in the 0–10 cm soil layer, and 14.3–19.0% lower in LMA but 43–52.1% higher in MA under S. superba than that under C. lanceolata and M. macclurei in the 10–20 cm soil layer. Moreover, the contribution of microbial residues to SOC was 44.4–47.5% higher under S. superba than under the other tree species. These findings suggest a higher stability of microbial residues under S. superba than that under the other studied tree species. Conclusions Our results demonstrate that tree species influence long-term microbial persistence in forest soils by affecting accumulation and stabilization of microbial residues.

Soil microbes mediate soil organic carbon (SOC) storage by affecting microbial residue carbon (C) in terrestrial ecosystems, a main source of SOC. However, how microbial residue C accumulation changes during the conversion of subtropical primary forest to plantations and the role of soil microbial community structure in regulating these changes remain unclear. Here, effects of conversion from forest on microbial residue C accumulation in three plantations, including tea (Camellia sinensis var. assamica), walnut (Juglans regia), and macadamia (Macadamia integrifolia). We assessed amino sugars content and the relative importance of soil microbial community structure, soil fertility, and aboveground biomass in four forest types in southwest Yunnan province, China. Our results show that total microbial residue C accounted for 27.8 % of SOC on average across all forest types, and fungal residue C contributed more to SOC than bacterial residue C across different forest types. Conversion from primary forest decreased fungal, bacterial, and total microbial residue C content in all plantation types except tea. Microbial residue C contents was significantly lower in the macadamia plantation than in the primary forest and the tea plantation. Fungal and total microbial residue C content increased with increasing soil microbial community composition, soil fungal abundance, and soil fertility. Soil fertility regulated fungal, bacterial, and total microbial residue C accumulation, which was major determinant of microbial residue C via its influence on soil fungal and bacterial abundance. Overall, we found that soil fungal abundance contributed more to microbial residue C accumulation than change in soil microbial community composition. We also found that soil bacterial abundance was negatively correlated with fungal and microbial residue C, while soil fungal abundance was positively related to microbial residue C accumulation. Ascomycota was most important phylum regulating microbial residue C. These findings suggest that soil fungal and bacterial abundance and soil fertility are the principal regulators of microbial residue C accumulation during the conversion from primary forest to different plantations.

Agroforestry management practices governed soil organic carbon (SOC) and microbial community structure in terrestrial ecosystems, yet the effect of these practices on microbial necromass carbon (C) remain poorly understood in a subtropical region. Here, we compared the differences in fungal, bacterial, and microbial necromass C (indicated by amino sugars) and their contributions to SOC among different forest types including macadamia monoculture plantation (MMP) and macadamia-based agroforestry systems intercropping with dasheen (MDAS), konjac (MKAS), and maize (MMAS) in the Lincang city, southwest Yunnan province, China, and assessed the impact of aboveground biomass, soil fertility, and soil microbial community structure on microbial necromass C and its contribution to SOC. Compared with monoculture plantation, macadamia-based agroforestry decreased SOC, and changed significantly soil microbial α diversity, β diversity, and microbial necromass C and its contribution to SOC (P

In this study, we investigated the seasonal changes in enzyme activities and microbial necromass carbon (C) in the bulk and rhizosphere soils of different halophytes (shrubs, grasses, and forbs) in an inland saline ecosystem in China. We found that the soil enzyme activities and microbial necromass C were 45–646% higher in rhizosphere soils than bulk soils regardless of the season and halophyte functional group. The activities of soil enzymes and bacterial necromass C were highest for forbs (4.9–172.3 nmol g−1 h−1 and 473.2 mg kg−1, respectively), and grasses had the highest fungal necromass C (FN-C) and total necromass C/soil organic C (TN-C/SOC) ratio. Moreover, the soil enzyme activities were higher in the late season stage (4.0–154.0 nmol g−1 h−1) than the early (3.6–132.1 nmol g−1 h−1) and middle (3.8–128.9 nmol g−1 h−1) season stages. FN-C and TN-C/SOC ratio were significantly higher in the middle season than the early and late seasons. Redundancy analysis showed that the enzyme activities and microbial necromass C mainly depended on the soil physicochemical properties, season, and halophyte functional group. Our results indicate that microbial turnover was consistently faster in rhizosphere soil than bulk soil in an inland saline ecosystem, and forbs could be used as pioneer species to improve microbial turnover during the phytoremediation of saline ecosystems. [ABSTRACT FROM AUTHOR]

Microbial necromass accrual via anabolism is an important process contributing to the formation and accumulation of stable soil organic C (SOC). Both substrates and microbial community traits impact the rate and efficiency of microbial biomass production, yet their effects on necromass accumulation patterns and efficiency remain unclear. Here we selected six substrates to investigate substrate and community regulations on microbial necromass accumulation over a 476-day model soil incubation including three stages (microbial growth–starvation–reactivation) with varied supply of substrates or 13C-labeled glucose. Microbial respiration, the composition of main microbial groups, and necromass (amino sugars) production were examined along with 13C analysis to compare necromass accumulation from new OC and native SOC. We found that relative to fast-decomposing substrates, slow-decomposing substrate like lignin induced slow but steady necromass accrual in a long term. Exogenous glucose input stimulated necromass accumulation from new and native SOC during reactivation, especially in C (or energy)-limited model soils. Furthermore, the accumulation efficiency of amino sugars sourced from SOC and 13C-labeled glucose were positively related, suggesting microbial communities and soil properties affect necromass accrual efficiency. However, there was quite some scatter in the correlation, suggesting potential substrate effect and uncertainty in this relationship. Hence, the efficiency of soil "microbial C pump" (i.e., microbial transformation of exogenous substrates into microbial byproducts) fueled by exogenous substrate and native SOC needs to be further investigated. Collectively, these findings provide new information on the dynamics and efficiency of microbial necromass accumulation from different substrates in soils. [ABSTRACT FROM AUTHOR]

CO2 separation with harmful chemicals will damage the environment. It is essential to explore greener solvents that are producible from renewable resources such as biomass. The suitability of N‐methyl‐D‐glucamine (MG), also known as meglumine, for capturing CO2, was explored in this work. This nontoxic amino sugar, which is derived from sorbitol, represents a renewable bio‐solvent. It was found that MG is especially reactive with CO2. Trials were performed in a stirred cell reactor with a flat gas–liquid interface between 303 and 313 K. The values of the pseudo‐first‐order reaction rate constant, reaction orders, and activation energy were found. The loading capacity (α) of 0.5 M MG solution was measured at T = 308 K. For a typical value of α = 0.524 mol CO2/mol MG, the corresponding equilibrium partial pressure of CO2 was 22 kPa. Finally, it was found that the catalyst Al2O3 aided in the desorption of CO2‐loaded MG solutions. Desorption efficiency using Al2O3 was higher (74%) than that achieved without this catalyst (45%). It is thus clear that MG represents a potential solvent for improved CO2 separation from gases. [ABSTRACT FROM AUTHOR]

To achieve long‐term increases in soil organic carbon (SOC) storage, it is essential to understand the effects of carbon management strategies on SOC formation pathways, particularly through changes in microbial necromass carbon (MNC) and dissolved organic carbon (DOC). Using a 14‐year field study, we demonstrate that both biochar and maize straw lifted the SOC ceiling, but through different pathways. Biochar, while raising SOC and DOC content, decreased substrate degradability by increasing carbon aromaticity. This resulted in suppressed microbial abundance and enzyme activity, which lowered soil respiration, weakened in vivo turnover and ex vivo modification for MNC production (i.e., low microbial carbon pump "efficacy"), and led to lower efficiency in decomposing MNC, ultimately resulting in the net accumulation of SOC and MNC. In contrast, straw incorporation increased the content and decreased the aromaticity of SOC and DOC. The enhanced SOC degradability and soil nutrient content, such as total nitrogen and total phosphorous, stimulated the microbial population and activity, thereby boosting soil respiration and enhancing microbial carbon pump "efficacy" for MNC production. The total C added to biochar and straw plots were estimated as 27.3–54.5 and 41.4 Mg C ha−1, respectively. Our results demonstrated that biochar was more efficient in lifting the SOC stock via exogenous stable carbon input and MNC stabilization, although the latter showed low "efficacy". Meanwhile, straw incorporation significantly promoted net MNC accumulation but also stimulated SOC mineralization, resulting in a smaller increase in SOC content (by 50%) compared to biochar (by 53%–102%). The results address the decadal‐scale effects of biochar and straw application on the formation of the stable organic carbon pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content. [ABSTRACT FROM AUTHOR]

Background: Microbial residues are significant contributors to stable soil organic carbon (SOC). Soil aggregates effectively protect microbial residues against decomposition; thus, microbial residue accumulation and distribution among soil aggregates determine long-term SOC stability. However, how tree species influence accumulation and distribution of soil microbial residues remains largely unknown, hindering the chances to develop policies for SOC management. Here, we investigated microbial residue accumulation and distribution in soil aggregates under four subtropical tree species (Cunninghamia lanceolata, Pinus massoniana, Michelia macclurei, and Schima superba) after 29 years of afforestation. Results: Accumulation of microbial residues in the 0–10 cm soil layer was 13.8–26.7% higher under S. superba than that under the other tree species. A structural equation model revealed that tree species affected the accumulation of microbial residues directly by altering fungal biomass. Additionally, tree species significantly affected microbial residue distribution and contribution to SOC in the top 20 cm soil. In particular, microbial residue distribution was 17.2–33.4% lower in large macro-aggregates (LMA) but 60.1–140.7% higher in micro-aggregates (MA) under S. superba than that under the other species in the 0–10 cm soil layer, and 14.3–19.0% lower in LMA but 43–52.1% higher in MA under S. superba than that under C. lanceolata and M. macclurei in the 10–20 cm soil layer. Moreover, the contribution of microbial residues to SOC was 44.4–47.5% higher under S. superba than under the other tree species. These findings suggest a higher stability of microbial residues under S. superba than that under the other studied tree species. Conclusions: Our results demonstrate that tree species influence long-term microbial persistence in forest soils by affecting accumulation and stabilization of microbial residues. [ABSTRACT FROM AUTHOR]

Carbohydrates are a ubiquitous constituent of organisms and contribute significantly to sedimentary organic carbon pools. Yet, the factors that control the degradation and long-term preservation of sedimentary carbohydrates are not well understood. Here, we investigate carbohydrate pool sizes and chemical compositions in high-altitude, meromictic Lake Cadagno (Switzerland) over a 13,500-year-old sedimentary succession that has recorded past changes from oxic to anoxic conditions and consists mostly of intercalations of lacustrine sediments and terrestrial-derived sediments. Analyses of the organic matter chemical composition by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) show that carbohydrates are selectively preserved over other organic matter constituents over time. The carbohydrate pyrolysis products levosugars (potentially cellulose-derived) and (alkyl)furans and furanones (potentially pectin-derived) dominate both lacustrine and terrestrially derived sediment layers, suggesting aquatic and terrestrial-derived sources of these compounds. Carbohydrate monomer analyses indicate galactose and glucose as dominant monomers and show no clear differences between aquatic and terrestrial organic matter. No clear impacts of past changes in redox conditions on carbohydrate compositions were observed. Our study shows that carbohydrates are a major contributor to sedimentary organic carbon burial in Lake Cadagno and indicates the effective preservation of both aquatic and terrestrial derived carbohydrates over millennia in lake sediments.

Elevated ozone (eO 3) and atmospheric nitrogen (N) deposition are important climate change components that can affect plant growth and plant-soil-microbe interactions. However, the understanding of how eO 3 and its interaction with N deposition affect soil microbially mediated carbon (C) cycling and the fate of soil C stocks is limited. This study aimed to test how eO 3 and N deposition affected soil microbial metrics (i.e., respiration, enzyme activities, biomass, necromass, and community composition) and resulting soil organic C (SOC) fractions in the rhizosphere of poplar plantations with different sensitivity to O 3. Exposure to O 3 and/or N deposition for four years was conducted within a free-air O 3 concentration-enrichment facility. Elevated O 3 reduced soil microbial respiration and biomass C but enhanced the enzymatic acquisition of C (i.e., potential soil hydrolase and oxidase activity) and shifted to a fungi-dominated community composition. These responses suggest that microbial C availability decreased and microbes allocated more energy to obtain C and nutrients from biochemically resistant substrates under eO 3. Elevated O 3 decreased bacterial necromass C and total necromass C, which could explain the observed decreases in mineral-associated organic C and SOC. The effects of eO 3 on soil microbial C availability and community composition were strengthened by N addition, whereas there were no differences in the below-ground effects of eO 3 between the two poplar clones. Taken together, the increased soil extracellular enzyme activities and slightly increased particulate organic C content suggest that the microbial C pump pathway via microbial ex vivo modification was strengthened by eO 3 , whereas the pathway via microbial in vivo turnover was weakened, as suggested by the decreases in soil microbial respiration, biomass, necromass, and mineral-associated organic C. Our study provides evidence that aboveground eO 3 effects on trees may affect belowground microbial processing of organic matter and ultimately the persistence of SOC. • Poplar plantations were exposed to elevated O 3 and N. • O 3 treatment increased soil enzyme activity and fungal abundance. • O 3 treatment reduced microbial respiration, biomass, and necromass. • O 3 treatment decreased soil mineral-associated rather than particulate organic carbon. • N addition strengthened O 3 effects on soil microbial C availability and community composition. [ABSTRACT FROM AUTHOR]

Saline-sodic soils have experienced severe organic carbon loss worldwide. In recent years, various types of cropping systems have been employed to reclaim saline-sodic wastelands, with the aim of increasing food production and improving soil conditions. However, the complex effects of this rapid and intense land-use change on soil organic carbon (SOC) accumulation and stability remain unclear. In this study, we compared how these effects varied across unperturbed saline-sodic wasteland, paddy fields, upland fields, and upland fields converted from paddy fields (CF) in the Songnen Plain, northeast China. Our assessment of plant- and microbial-derived carbon biomarkers, including lignin phenols, amino sugars, and glomalin-related soil proteins, revealed that the cultivation of saline-sodic wasteland increased total SOC by increasing particulate, mineral-associated, and labile organic carbon. Across cropping systems, the largest increase in SOC (217.77 %) was measured under long-term cultivation. Microbial-derived carbon was the primary contributor to SOC in saline-sodic farmland, but the proportion of SOC formed by plant-derived carbon increased under long-term cultivation. Our analysis of lignin phenols and soil enzymes (cellulase and ligninase) suggests that microbial decomposition of plant-derived carbon was enhanced in long-term compared to short-term farmland. Despite greater overall accumulation of plant- and microbial-derived carbon in CF, the stability of microbial-derived carbon in this cropping system was relatively low due to lower ratios of glucosamine to muramic acid. Additionally, random forest modelling indicates that the increases in microbial biomass and improvements in basic soil properties associated with the cultivation of saline-sodic wasteland were the key factors influencing plant- and microbial-derived carbon. These findings demonstrate that the cultivation of saline-sodic wasteland increases carbon sequestration in the soil by increasing both plant- and microbial-derived SOC. [Display omitted] • Farmland reclamation effectively enhances saline-sodic soil SOC storage. • Converting saline-sodic paddy to upland fields still achieves accumulation of plant- and microbial-derived carbon. • Lignin phenols, amino sugars, and glomalin-related soil proteins has different contribution to SOC. [ABSTRACT FROM AUTHOR]

Soil microbial residues play an important role in the formation and stabilization of soil organic matter and can be quantitatively characterized by amino sugars. However, the response of soil microbial residues to agricultural cultivation in karst areas remains unclear. In this study, we collected soil samples from natural reserved land as well as five plantation forests dominated by Citrus trees cultivated for 0, 1, 5, 15, 30 years to examine the effects of agricultural cultivation on the content of microbial residues (amino sugar analysis). Results showed that: (1) Soil Amino Sugars (ASs) contents were significantly reduced after agricultural cultivation along with the sharp decrease in soil organic carbon (SOC). After 30 years of cultivation, the contents of total ASs, glucosamine (GluN), galactosamine (GalN), and muramic acid (MurA) in cultivated soils decreased by 58.22%, 55.30%, 27.11%, respectively, compared with 0 yr.; (2) Microbial residual carbon contribution to SOC increased from 34.11% to 81.33% after 30 years of cultivation, including fungal residual carbon (FRC) (25.79% to 48.6%) and bacterial residual carbon (BRC) (8.32% to 32.72%); (3) Soil GluN/MurA values tended to decrease with increasing cultivation years. The results highlight the significant effect of cultivation years on amino sugar accumulation. It indicates that the years of reclamation in karst areas have different impacts on the organic fractions derived from various microbial communities in the soil organic matter pool, and the microbial residues indicated by amino sugar are of great significance for the interception of soil organic matter. [ABSTRACT FROM AUTHOR]

Mineral-associated organic matter (MAOM) constitutes a significant portion of carbon (C) pools in wetlands, determining their role as C sinks or sources. Nevertheless, detailed knowledge of the response of MAOM formation pathways to wetland restoration is lacking. Here, we collected 0-20 cm soil samples from two typical wetlands (meadow and peat wetlands) subjected to both grazing and restoration treatments (through micro dam construction) in the Zoige area. Lignin phenols and amino sugars within the MAOM fraction were analysed to clarify the MAOM formation pathways and their potential contributions to MAOM formation. The results demonstrated that both meadow and peat wetland restoration enhanced MAOM sequestration. Compared to grazed sites, restored meadow wetlands significantly increased the mineral-associated organic carbon (MAOC) content in soils but not the C content of the MAOM fraction; restored peat wetlands increased the C content of the MAOM fraction by 58% but not the MAOC content in soils. Notably, plant-derived C and microbial necromass C strongly and dominantly influenced the C content of the MAOM fraction in the meadow (path coefficient = 0.73) and peat wetlands (path coefficient = 0.75), respectively. Compared with those in the grazed peat wetlands, the MAOM fraction in restored peat wetlands contained 1.93, 1.61, and 2.09 times higher total, bacterial, and fungal necromass C contents, respectively. Moreover, soil properties influence lignin phenols and necromass C in conjunction with the C content of the MAOM fraction rather than directly. It seems reasonable to assume that meadow wetland restoration from grazing enhanced MAOM formation in soils via the accumulation of lignin phenols (through the "direct sorption" pathway). Peat wetland restoration from grazing enhanced MAOM formation in soils via the accumulation of lignin phenols (through the "direct sorption" pathway) and the "microbial turnover" pathway., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Supramolecular hydrogels can be obtained via self-assembly of small molecules in aqueous environments. In this study, we describe the development of oxidation-responsive supramolecular hydrogels comprising glucosamine derivatives with an aryl sulfide group. We demonstrate that hydrogen peroxide can induce a gel-sol transition through the oxidation of the sulfide group to the corresponding sulfoxide. Furthermore, we show that this oxidation responsiveness can be extended to photo-responsiveness with the aid of a photosensitizer., (© 2024 Wiley-VCH GmbH.)

Transformation of glycals to 2,3‐di‐substituted‐3‐dexoy‐glycals were achieved by sequential C2 alkenylation of pseudoglycals followed by capture of nucleophiles at C3 position. Anomeric linked N‐(glycosyloxy) acetamides group assisted innate C2‐H activation of pseudoglycals under palladium catalysis is achieved. The synthesized C2 alkenylated products were further attacked by thio/amino nucleophiles at C3 position under basic conditions in stereo‐selective fashion to generate 2,3‐branched glycals with the elimination of directing groups and translocation of double bond. Different control experiments were conducted to establish the role of directing groups in C−H functionalization of pseudoglycals and reason for selectivity. [ABSTRACT FROM AUTHOR]

Root activity creates a unique microbial hotspot in the rhizosphere and profoundly regulates soil carbon (C) dynamics, but empirical assessments of the soil microbial carbon pump (MCP, the iterative accumulation of necromass after microbial anabolism) and associated ecological consequences on soil C storage based on insight of the rhizosphere are still neglected, especially for different root functional modules.We assessed the soil MCP efficacy (i.e. the contribution of microbial necromass to SOC) by investigating the divergent contribution of microbial necromass based on amino sugar extrapolations to soil organic C (SOC) in the rhizosphere of two root functional modules (i.e. absorptive roots and transport roots) and the bulk soil in an alpine coniferous forest.The results showed that the MCP efficacy in both rhizosphere and bulk soil was more than 50%, suggesting that microbial necromass plays a key role in SOC formation. More importantly, absorptive roots drove a greater rhizosphere MCP efficacy (56%) than transport roots (51%).Synthesis. These observations suggest that the microbial necromass is a major contributor to SOC storage in both rhizosphere and bulk soil in alpine coniferous forests. The magnitude of the contribution of microbial necromass to rhizosphere SOC depends on root functional differentiation. Our study provides novel and direct empirical evidence for the active soil MCP functions in SOC sequestration from the perspective of the rhizosphere. [ABSTRACT FROM AUTHOR]

We presented a facile and scalable route for the synthesis of di-azido sugars via one-pot double inversion of the mono-benzoyl sugars by TBAN3 and studied the dependency pattern between solvent and protecting groups as well as the configuration of the neighboring and leaving groups. Moreover, we developed a chemical synthetic strategy for pseudaminic acid precursors (11 steps in 49%). Furthermore, we discussed the configuration of nonulosonic acid precursors for specificity of PseI and PmNanA enzymatic synthesis, permitting us to synthesize new nonulosonic acid derivatives for accessing Pse isomers.

Herin is reported a blue light-promoted (Ir[ d F(CF 3)ppy] 2 (dt bpy))PF 6 catalyzed method that synthesizes the 2-amino sugar analogues from glycals, N -aminopyridinium salts and alcohol. The reactions obtained two diastereomers and the results were not influenced by the kinds of glycals. The advantage of this method is that not only different nitrogen-containing functional groups can be introduced at the C-2 position of the glycals, but also different oxygen-containing functional groups can be attached at C-1 by using methanol, t ert -butanol, and water in the reaction. [Display omitted] • Visible light-promoted Ir-catalyzed reaction could achieve the synthesis of 1-OR 1 -2-NHR 2 -sugar from glycals. • The reaction gave two diastereomers with trans -configurations of C1–H and C2–H. • The kinds of glycals did not influence the selectivity of configurations. [ABSTRACT FROM AUTHOR]

Microbial necromass carbon (MNC) is a key soil organic carbon (SOC) pool. Soil aggregates and minerals play pivotal roles in controlling soil carbon storage. Although soil minerals and aggregates are tightly linked to parent materials, it is uncertain whether the relative importance of aggregates and minerals in governing MNC varies depending on soil parent materials. In this study, we determined the MNC content in forest soils originating from two contrasting soil parent materials, namely karst (carbonate rocks) and non-karst soils (clastic rocks) across a climatic gradient in southwest China. The MNC contents (24.5 ± 0.8 mg g−1 in karst and 24.1 ± 1.8 mg g−1 in non-karst soils) and their respective contribution to SOC (43.7 ± 1.3 % in karst and 41.1 ± 1.4 % in non-karst soils) were similar between the two parent materials. In karst soils, MNC was influenced by aggregates rather than minerals, whereas the opposite was true in non-karst soils. A higher proportion of microaggregates directly increased the MNC content in karst soils, whereas greater mineral contents indirectly increased the MNC through their effects on microbial biomass carbon. The divergent effects of aggregates and minerals on MNC were predominantly attributed to the formation of secondary carbonate crystals in calcium-rich karst soils as well as to the differences in pH between karst and non-karst soils. Additionally, climate (mean annual temperature and precipitation) and vegetation properties (aboveground biomass or richness) indirectly affected the MNC through their effects on aggregates or minerals in karst and non-karst soils. Consequently, the influence of soil aggregates and minerals on microbially derived carbon is mediated by the parent material. Our findings emphasize the importance of considering lithology-dependent drivers in predicting soil carbon accumulation, particularly in relation to the stability of microbial-derived carbon. [Display omitted] • Microbial necromass carbon accumulation is similar between karst and non-karst soils. • Soil aggregates, not minerals, affect microbial necromass carbon in karst soils. • Soil minerals, not aggregates, influence microbial necromass carbon in non-karst soils. • Lithology mediates physical-chemical protection on microbial necromass carbon. [ABSTRACT FROM AUTHOR]

Precision and efficient management of organic substitution fertilization is crucial in balancing soil health, environmental risks, and economic benefits for intensive crop cultivation. However, effectively determining the optimal organic substitution ratio in vegetable production remains uncertain and still relatively unexplored. We conducted a five-year vegetable field experiment and established four nitrogen-equivalent fertilization treatments: mineral fertilizer alone, and organic fertilizer substituting a quarter, half, and entirety of the mineral nitrogen. Employing a specialized multi-level fuzzy comprehensive evaluation model, our study assessed impacts of different organic substitution ratios on soil qualities, microbial diversity, vegetable yield and quality, environmental risks, and economic benefits in sustainable vegetable production of eastern China. Our results showed that the 50% organic substitution was optimal, significantly improving soil qualities and microbial characteristics, particularly in the topsoil layer. Compared to the control, this approach significantly reduced methane by 6.6–48.3%, nitrous oxide by 49.5–79.1%, and nitric oxide by 36.5–50.0%, while enhancing vegetable yield by 16.0–28.3% and its five-year average stability as well as quality as evidenced by increased protein, soluble sugar, and vitamin C contents. Economic analysis revealed that while it maximized environmental benefits, complete organic substitution did not consistently yield positive economic returns. In contrast, a 50% substitution ratio was identified as the most economically viable, representing a sustainable compromise that balances environmental health with economic feasibility. Further modeling analysis indicated an optimal comprehensive range between 42.9% and 64.5% for achieving the best balance of multiple objectives in vegetable fields. The study underscores the intricate organic substitution effects on intensive vegetable production, highlighting the necessity for tailored organic substitution strategies that integrate environmental sustainability with agricultural productivity and economic practicality. [Display omitted] ● Organic substitution assessed by field measures and multi-level fuzzy comprehensive model ● Organic substitution enhanced soil health, vegetable quality, and economic benefits ● Half organic substitution improved yield stability, soil qualities, income, and environments ● 42.9%-64.5% was recommended as organic substitution ratio for sustainable vegetable production [ABSTRACT FROM AUTHOR]

[Display omitted] • Two new amino sugars and six known alkaloids were isolated. • Amino sugars from Daphniphyllum plant are reported for the first time. • Known alkaloids showed moderate to weak activity against HCV infection. A phytochemical investigation performed on the leaves of Daphniphyllum himalaense has led to the characterization of two new amino sugars (1 and 2) and six known daphniphyllum alkaloids. The structures of new compounds were determined based on the interpretation of spectroscopic data. Some of the alkaloids were found to possess moderate to weak activity against the hepatitis C virus infection. [ABSTRACT FROM AUTHOR]

Microorganisms play a crucial role in regulating the turnover and transformation of soil organic carbon (SOC), whereas microbial contribution to SOC formation and storage is still unclear in coastal wetlands. In this study, we collected topsoil (0–20 cm) with 7 salinity concentrations and explored the shifts in microbial residues [represented by amino sugar (AS)] and their contribution to the SOC pool of coastal wetlands in the Yellow River delta. The gradually increasing soil salinity reduced soil water content (SWC), SOC, and soil nitrogen (N), especially in high salinity soils of coastal wetlands. Total ASs and their ratio to SOC, respectively, decreased by 90.56 and 66.35% from low salinity to high salinity soils, indicating that coastal wetlands with high salinity restrained microbial residue accumulation and microbial residue-C retention in the SOC pool. Together with redundancy analysis and path analysis, we found that SWC, pH, SOC, soil N, and glucosamine/muramic arid were positively associated with the ratio of ASs to SOC. The higher available soil resource (i.e., water, C substrate, and nutrient) increased microbial residue accumulation, promoting microbial derived-C contribution to SOC in low salinity coastal wetlands. The greatly decreased microbial residue contribution to SOC might be ascribed to microbial stress strategy and low available C substrate in coastal wetlands with high salinity concentration. Additionally, the gradually increasing salinity reduced fungal residue contribution to SOC but did not change bacterial residue contribution to SOC. These findings indicated that changed fungal residues would substantially influence SOC storage. Our study elucidates microbial contribution to SOC pool through residue reservoir in coastal wetlands and pushes microbial metabolites to a new application in global wetland SOC cycling.

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The broth of sea cucumber was decolorized with mineral sorbents, as perlite and bentonite, and with chitosans of crab carapace and shrimp shell. The chitosans were the most effective in sorption and subsequent removal of the protein-pigment complex, providing the decolorization degree of 35–55 %. Besides, the content of glycosides in the broth was twice decreased. The amino sugars content changed in dependence on the chitosan origin: the chitosan of crab carapace did not influence on this parameter, but the chitosan of shrimp shell caused its halving. For the optimal combination of chemical compounds in the broth, the chitosan with high molecular weight (1300 kDa) extracted from crab carapace should be used for decolorizing. Preliminary fermentation of the broth with Protamex increased concentration of biologically active peptides with low molecular weight in the solution. The fermented and decolorized broth of sea cucumber has good organoleptic properties and high content of biologically active components, as glycosides, amino sugars and low molecular weight peptides, so could be used as the basis for nonalcoholic tonic drinks.

Soil microbial residues play an important role in the formation and stabilization of soil organic matter and can be quantitatively characterized by amino sugars. However, the response of soil microbial residues to agricultural cultivation in karst areas remains unclear. In this study, we collected soil samples from natural reserved land as well as five plantation forests dominated by Citrus trees cultivated for 0, 1, 5, 15, 30 years to examine the effects of agricultural cultivation on the content of microbial residues (amino sugar analysis). Results showed that: (1) Soil Amino Sugars (ASs) contents were significantly reduced after agricultural cultivation along with the sharp decrease in soil organic carbon (SOC). After 30 years of cultivation, the contents of total ASs, glucosamine (GluN), galactosamine (GalN), and muramic acid (MurA) in cultivated soils decreased by 58.22%, 55.30%, 27.11%, respectively, compared with 0 yr.; (2) Microbial residual carbon contribution to SOC increased from 34.11% to 81.33% after 30 years of cultivation, including fungal residual carbon (FRC) (25.79% to 48.6%) and bacterial residual carbon (BRC) (8.32% to 32.72%); (3) Soil GluN/MurA values tended to decrease with increasing cultivation years. The results highlight the significant effect of cultivation years on amino sugar accumulation. It indicates that the years of reclamation in karst areas have different impacts on the organic fractions derived from various microbial communities in the soil organic matter pool, and the microbial residues indicated by amino sugar are of great significance for the interception of soil organic matter.

• Forest restoration increases lignin and microbial necromass in the subsoil. • Lignin decreased faster in topsoil's particulate organic matte than amino sugars. • Microbial necromass builds quicker in subsoil's mineral-bound organic than lignin. • Subtropical forest restoration has a greater impact on subsoil than topsoil. Soil organic carbon (SOC) represents the largest carbon reservoir in terrestrial ecosystems. Therefore, understanding how to enhance SOC is crucial for the global carbon cycle and atmospheric CO 2 removal. While there has been reported on SOC accumulation following forest restoration efforts, changes in plant lignin and microbial necromass across soil fractions and depths remain unclear. To address this gap, we investigated the SOC-standardized concentrations of lignin phenols and amino sugars in bulk soil and soil fractions (particulate organic matter (POM) and mineral-associated organic matter (MAOM)) during subtropical forest restoration, as tracers for change in plant lignin components and microbial necromass respectively. Our findings indicate that forest restoration does not affect SOC concentrations, but does result in changes in plant lignin and microbial necromass. Specifically, in the subsoil, lignin phenols and amino sugars concentrations in bulk soil and soil fractions rise significantly with restoration time, with lignin phenols and amino sugars concentrations in bulk soil rising by 29.6% and 53.0%, respectively. This suggests that as forests recover, lignin and microbial necromass have a higher contribution to SOC accumulation in the subsoil, while the contribution of low-molecular plant-derived organic matter decreases. The relative change rate of lignin phenols (relative to SOC) is greater than that of amino sugars in POM in the topsoil, while in the subsoil, the relative change rate of amino sugars in MAOM is greater than that of lignin phenols. These results indicate that lignin in POM declines more rapidly than amino sugars during restoration, whereas in MAOM, amino sugars accumulate faster than lignin. Overall, these findings provide important insights into the regulation of SOC accumulation during forest restoration by the combination of plant lignin and microbial necromass in various stabilization pathways. [ABSTRACT FROM AUTHOR]

• Conversion of farmland to grassland reduced microbial residue carbon content especially fungal residue carbon content. • Conversion of farmland to shrub forest increased microbial residue carbon content especially bacterial residue carbon content. • Microbial residue carbon accounted for a significant proportion of soil organic carbon. • Microbial residue carbon contribution to soil organic carbon increased after returning farmland to shrub forest and grassland. Microbial residue carbon (C) serves as a significant source of soil organic carbon (SOC). However, the contribution of microbial residue C to SOC accumulation after the restoration of farmland vegetation remains unclear, making it challenging to comprehend the role of microorganisms in the accumulation and transformation of SOC after vegetation restoration on farmland. Based on field investigations in Guinan County, Qinghai Province, our study focused on the microbial residue C content and its contribution to SOC in farmland, grassland, and shrub forest, employing the analysis of biomarkers. The results indicated that the microbial residue C content increased with the rise of SOC, soil total nitrogen (STN), and enzyme activities. Compared to farmland, grassland displayed significantly lower levels of SOC and STN, leading to reduced microbial residue C content, notably impacting the C content of fungal residues. Despite slightly lower levels of SOC and STN compared to farmland, shrub forest exhibited higher soil microbial residue C content, notably within bacterial residue C, due to elevated soil enzyme activities. The contribution of microbial residue C to SOC decreased as SOC content increased. In farmland boasting higher SOC content, the contribution of microbial residue C to SOC was notably lower compared to shrub forest and grassland with lower SOC content. In conclusion, compared to farmland, both shrub forest and grassland exhibited higher contributions of microbial residue C to SOC, which is favorable for the sequestration of stable SOC. [ABSTRACT FROM AUTHOR]

Amino sugars, particularly glucosamine (GlcN) and N-acetylglucosamine (GlcNAc), are abundant carbon and nitrogen sources supplied in host secretions and in the diet to the biofilms colonizing the human oral cavity. Evidence is emerging that these amino sugars provide ecological advantages to beneficial commensals over oral pathogens and pathobionts. Here, we performed transcriptome analysis on Streptococcus mutans and Streptococcus gordonii growing in single-species or dual-species cultures with glucose, GlcN, or GlcNAc as the primary carbohydrate source. Compared to glucose, GlcN caused drastic transcriptomic shifts in each species of bacteria when it was cultured alone. Likewise, cocultivation in the presence of GlcN yielded transcriptomic profiles that were dramatically different from the single-species results from GlcN-grown cells. In contrast, GlcNAc elicited only minor changes in the transcriptome of either organism in single- and dual-species cultures. Interestingly, genes involved in pyruvate metabolism were among the most significantly affected by GlcN in both species, and these changes were consistent with measurements of pyruvate in culture supernatants. Differing from what was found in a previous report, growth of S. mutans alone with GlcN inhibited the expression of multiple operons required for mutacin production. Cocultivation with S. gordonii consistently increased the expression of two manganese transporter operons (slo and mntH) and decreased expression of mutacin genes in S. mutans. Conversely, S. gordonii appeared to be less affected by the presence of S. mutans but did show increases in genes for biosynthetic processes in the cocultures. In conclusion, amino sugars profoundly alter the interactions between pathogenic and commensal streptococci by reprogramming central metabolism. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mowing can facilitate the incorporation of cover crop shoots into soil and improve the properties of soils in apple orchards. This article evaluated how apple orchard soil responds to the decomposition of the shoot residues of three cover crops[native mixed herbs (NMS), red clover (RCS), and ryegrass (RES)] in terms of microbial metabolism and biomass, and discussed the relationships between microbial responses and shoot chemistry. The chemical composition of shoots was analysed and a buried bag experiment was carried out to simulate shoot decomposition in an apple orchard. The results revealed significant differences in the chemical compositions and shoot C:N ratios (NMS: 10.9, RCS: 19.1, and RES: 12.9) of the three cover crops. The decomposition of the cover crop shoots promoted microbial metabolism and boosted soil bacterial reproduction (increase in the biomass indicator muramic acid: 19.44, 124.15, and 14.83 mg kg−1, respectively. But there are different types of effects on soil fungal reproduction (change in the biomass indicator glucosamine: 712.51, 887.45, and 103.97 mg kg−1), and they are obviously negative, significantly positive, and non-significant respectively. Thus, the native mixed herbs and red clover are preferable swards for better shoot enhancement in apple orchard. [ABSTRACT FROM AUTHOR]

No-tillage (NT) can enhance the accumulation of soil organic carbon (SOC), thereby aiding in climate change mitigation and improving soil fertility. However, the relations of soil microbial abundance, composition, and necromass to SOC increase under NT are still unclear, limiting the knowledge of SOC stabilization. We performed a 5-year paddy field experiment in southern China including NT, reduced tillage (RT) and conventional tillage (CT). Soil microbial necromass C (MC, including fungal and bacterial necromass C, FC, and BC) were analyzed, as well as soil bacterial and fungal community composition. At a depth of 0–10 cm, NT increased FC (by 48.6 %–50.2 %, P < 0.05), BC (28.6 %–41.7 %), and MC (38.5 %–45.1 %, P < 0.05) but did not significantly alter the FC/BC and MC/SOC ratios. The increase rate of MC (NT vs. CT and RT) was 12.8–16.2 % higher than that of total SOC. Compared with 0–10 cm and 10–20 cm, the MC/SOC ratio was 12.5 %–14.1 % lower at 20–30 cm. Linear regression indicated significant positive correlations of SOC with MC, BC, and FC, whereas no significant correlation was found between bacterial (or fungal) α-diversity (expressed by Shannon index) and BC (or FC). The Random Forest Model showed that several important fungal and bacterial Amplicon Sequence Variants (ASVs) explained 14 %–73 % of the FC and BC variations. Therefore, the composition of the microbial community may play a pivotal role in driving the accumulation of MC. Short-term NT in rice paddies resulted in increased levels of both MC and SOC. Notably, the rate of increase in MC exceeded that of SOC, suggesting the potential for SOC stabilization. • 5-Year no-tillage increased microbial-derived C in paddy soil. • Microbial composition explained 14–73 % of microbial-derived C variation. • The SOC is positively related with fungal and bacterial necromass C. • 5-Year no-tillage did not change microbial-derived C/SOC ratio. [ABSTRACT FROM AUTHOR]

Microbial necromass carbon (MNC) is one of the primary sources of stable soil organic carbon (SOC), playing a crucial role in global carbon cycling. Despite its significance, the impact of tunnel construction, a commonly adopted human activity in railway development, on MNC and its underlying mechanisms remains underexplored. To address this gap, a field survey was conducted in shrubland ecosystems on the eastern edge of the Qinghai-Tibet Plateau. Our study aimed to investigate the influence of tunnel construction on MNC and its contribution to SOC along an altitudinal gradient (3240 m, 3420 m, and 3600 m) and at two soil depths (0–10 cm and 10–30 cm). Results indicated that tunnel construction did not exert a significant impact on SOC and MNC. However, it led to a substantial decrease in the contribution of MNC to SOC (15.6%–19.9% in tunnel-affected areas) compared to the control areas (19.04%–30.97%). This outcome was likely attributed to the decreased bacterial necromass carbon (BNC) and the increased input of underground plant-derived carbon. MNC at 10–30 cm was significantly lower than that at 0–10 cm, and it exhibited a notable decrease at 3420 m compared to both 3240 m and 3600 m. These observations were closely related to reduced carbon input and microbial necromass stability. Principal component structural equation modeling revealed that soil microbial activities were the most important for MNC and SOC accumulation. Consequently, tunnel construction influenced SOC formation by altering the relative contributions from plant and microbial sources. This study provides valuable evidence for assessing the impacts of engineering construction on SOC and its sources in the context of climate change. Moreover, it offers scientific support for ecosystem conservation and sustainable development in the Qinghai-Tibet Plateau region during engineering construction. • Tunnel construction reduced bacterial necromass carbon. • Tunnel construction had no impact on fungal necromass carbon. • Contribution of microbial necromass to SOC was reduced after tunnel construction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Converting primary forest to agricultural production decreased fungal, bacterial, and total microbial residue C. • Soil fungal abundance increased microbial residue C accumulation. • Soil bacterial abundance declined fungal and total microbial residue C accumulation. • Soil fertility improved fungal, bacterial, and total microbial residue C accumulation. Soil microbes mediate soil organic carbon (SOC) storage by affecting microbial residue carbon (C) in terrestrial ecosystems, a main source of SOC. However, how microbial residue C accumulation changes during the conversion of subtropical primary forest to plantations and the role of soil microbial community structure in regulating these changes remain unclear. Here, effects of conversion from forest on microbial residue C accumulation in three plantations, including tea (Camellia sinensis var. assamica), walnut (Juglans regia), and macadamia (Macadamia integrifolia). We assessed amino sugars content and the relative importance of soil microbial community structure, soil fertility, and aboveground biomass in four forest types in southwest Yunnan province, China. Our results show that total microbial residue C accounted for 27.8 % of SOC on average across all forest types, and fungal residue C contributed more to SOC than bacterial residue C across different forest types. Conversion from primary forest decreased fungal, bacterial, and total microbial residue C content in all plantation types except tea. Microbial residue C contents was significantly lower in the macadamia plantation than in the primary forest and the tea plantation. Fungal and total microbial residue C content increased with increasing soil microbial community composition, soil fungal abundance, and soil fertility. Soil fertility regulated fungal, bacterial, and total microbial residue C accumulation, which was major determinant of microbial residue C via its influence on soil fungal and bacterial abundance. Overall, we found that soil fungal abundance contributed more to microbial residue C accumulation than change in soil microbial community composition. We also found that soil bacterial abundance was negatively correlated with fungal and microbial residue C, while soil fungal abundance was positively related to microbial residue C accumulation. Ascomycota was most important phylum regulating microbial residue C. These findings suggest that soil fungal and bacterial abundance and soil fertility are the principal regulators of microbial residue C accumulation during the conversion from primary forest to different plantations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Macadamia-based agroforestry systems influence microbial necromass C and its contribution to SOC. • Soil fungal β diversity controlled and significant negative effect over microbial necromass C and its contribution to SOC. • Woody aboveground biomass indirectly affected microbial necromass C via soil fungal β diversity. Agroforestry management practices governed soil organic carbon (SOC) and microbial community structure in terrestrial ecosystems, yet the effect of these practices on microbial necromass carbon (C) remain poorly understood in a subtropical region. Here, we compared the differences in fungal, bacterial, and microbial necromass C (indicated by amino sugars) and their contributions to SOC among different forest types including macadamia monoculture plantation (MMP) and macadamia-based agroforestry systems intercropping with dasheen (MDAS), konjac (MKAS), and maize (MMAS) in the Lincang city, southwest Yunnan province, China, and assessed the impact of aboveground biomass, soil fertility, and soil microbial community structure on microbial necromass C and its contribution to SOC. Compared with monoculture plantation, macadamia-based agroforestry decreased SOC, and changed significantly soil microbial α diversity, β diversity, and microbial necromass C and its contribution to SOC (P < 0.01). Microbial necromass C and its contribution to SOC were no significant difference between MMP and MMAS. MDAS and MKAS had lower microbial necromass C than MMP (35.11 % and 63.62 %, respectively). SOC increased with increasing soil fungal and microbial necromass C among the agroforestry systems. Soil fertility was the most important factor affecting fungal (41.45 %), bacterial (33.84 %), and microbial necromass C (40.63 %). Importantly, soil fertility and fungal β diversity directly negatively affected soil fungal and microbial necromass C and their contributions to SOC. Furthermore, woody aboveground biomass affected microbial necromass C directly or indirectly via soil fungal β diversity. Overall, our findings suggest that soil fungal β diversity drove microbial necromass C accumulation and its contribution to SOC in a macadamia-based agroforestry systems, which reveal that sowing crop may be key considerations in mitigating climate change. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unmanaged Moso bamboo forest duration significantly affects plant-derived C content. • Leaving unmanaged for 7–10 and 11–14 years significantly affected microbial-derived C content. • Soil cation exchange capacity dominated the accumulation of plant-derived C. • Plant biomass soil nutrients dominated the accumulation of microbial-derived C. Moso bamboo (Phyllostachys pubescens) has a high carbon (C) sequestration capacity that can help mitigate global climate change. However, owing to strengthened environmental protection policies and rising labor costs, large areas of Moso bamboo forests have been left unmanaged after long-term intensive management. Consequently, the contribution of plant- and microbial-derived C as part of soil organic carbon (SOC) has not been reported in Moso bamboo forests. Here, we investigated the change of microbial necromass and plant-derived components in Moso bamboo forests with different unmanaged chronosequences (i.e., intensively managed currently or unmanaged for 2–5, 7–10, or 11–14 years), using biomarker. We observed that plant-derived C was significantly higher in unmanaged than in intensively managed forests and that the highest content was found in the forests left unmanaged for 7–10 years (3.69 g kg−1). No significant differences in microbial-derived C content were observed between Moso bamboo forests under intensive management and those left unmanaged for 2–5 years. However, compared with intensive management, left unmanaged for 7–10 and 11–14 years significantly increased microbial-derived C content. Overall, the quantitative importance of microbial-derived C as part of SOC was higher than that of plant-derived C (28.7–42.62 % vs 8.88–20.8 %, respectively). Moreover, we found that the major determinants of microbial- and plant-derived C were different. For microbial-derived C accumulation, plant biomass, total nitrogen, total phosphorus, and soluble organic C were the dominant factors, and for plant-derived C accumulation, soil cation exchange capacity was the dominant factor. These findings provide new information about the changes in SOC accumulation in Moso bamboo forests left unmanaged and highlight the different accumulation mechanisms of plant- and microbial-derived C. [ABSTRACT FROM AUTHOR]