Incubation Experiments Research Articles

Roles of estrogen receptors during sexual reversal in Pelodiscus sinensis.

The Chinese soft-shelled turtle, Pelodiscus sinensis, exhibits distinct sexual dimorphism, with the males growing faster and larger than the females. During breeding, all-male offspring can be obtained using 17β-estradiol (E2). However, the molecular mechanisms underlying E2-induced sexual reversal have not yet been elucidated. Previous studies have investigated the molecular sequence and expression characteristics of estrogen receptors (ERs). In this study, primary liver cells and embryos of P. sinensis were treated with ER agonists or inhibitors. Cell incubation experiments revealed that nuclear ERs (nERs) were the main pathway for the transmission of estrogen signals. Our results showed that ERα agonist (ERα-ag) upregulated the expression of Rspo1, whereas ERα inhibitor (ERα-Inh) downregulated its expression. The expression of Dmrt1 was enhanced after ERα-Inh + G-ag treatment, indicating that the regulation of male genes may not act through a single estrogen receptor, but a combination of ERs. In embryos, only the ERα-ag remarkably promoted the expression levels of Rspo1, Wnt4, and β-catenin, whereas the ERα-Inh had a suppressive effect. Additionally, Dmrt1, Amh, and Sox9 expression levels were downregulated after ERβ inhibitor (ERβ-Inh) treatment. GPER agonist (G-ag) has a significant promotion effect on Rspo1, Wnt4, and β-catenin, while the inhibitor G-Inh does not affect male-related genes. Overall, these results suggest that ERs play different roles during sexual reversal in P. sinensis and ERα may be the main carrier of estrogen-induced sexual reversal in P. sinensis. Further studies need to be performed to analyze the mechanism of ER action.

Microorganisms in subarctic soils are depleted of ribosomes under short-, medium-, and long-term warming

Abstract Physiological responses of soil microorganisms to global warming are important for soil ecosystem function and the terrestrial carbon cycle. Here, we investigate the effects of weeks, years, and decades of soil warming across seasons and time on the microbial protein biosynthesis machineries (i.e. ribosomes), the most abundant cellular macromolecular complexes, using RNA:DNA and RNA:MBC (microbial biomass carbon) ratios as proxies for cellular ribosome contents. We compared warmed soils and non-warmed controls of 15 replicated subarctic grassland and forest soil temperature gradients subject to natural geothermal warming. RNA:DNA ratios tended to be lower in the warmed soils during summer and autumn, independent of warming duration (6 weeks, 8–14 years, > 50 years), warming intensity (+3°C, +6°C, +9°C), and ecosystem type. With increasing temperatures RNA:MBC ratios were also decreasing. Additionally, seasonal RNA:DNA ratios of the consecutively sampled forest showed the same temperature-driven pattern. This suggests that subarctic soil microorganisms are depleted of ribosomes under warm conditions and the lack of consistent relationships with other physicochemical parameters besides temperature further suggests temperature as key driver. Furthermore, in incubation experiments, we measured significantly higher CO2 emission rates per unit of RNA from short- and long-term warmed soils compared to non-warmed controls. In conclusion, ribosome reduction may represent a widespread microbial physiological response to warming that offers a selective advantage at higher temperatures, as energy and matter can be reallocated from ribosome synthesis to other processes including substrate uptake and turnover. This way, ribosome reduction could have a substantial effect on soil carbon dynamics.

Organic matter decomposition in mountain peatlands: effects of substrate quality and peatland degradation

Abstract Background and Aims Peatlands occupy only 3% of Earth’s terrestrial lands but store about one-third of global soil carbon. However, these large carbon stocks are currently under threat due to peatland degradation, where altered hydrological balance could enhance peat oxidation; thus releasing large amounts of CO2 into the atmosphere. We investigated the interactive effects of substrate quality, peat depth and peatland degradation on the decomposition rate of organic matter in peatlands by way of a field incubation experiment. Methods We incubated high-quality fresh peat and a lower-quality degraded peat substrate at three different depths (5, 15, and 30 cm) in two (intact and degraded) mountain peatlands for 18 months. Our results indicated that there is a significant interactive effect of substrate quality, peat depth, and peatland type on the peat decomposition rate. Results The fresh peat showed significantly higher decomposition rates than the degraded peat substrate, likely due to the high percentage of bioavailable carbon in the fresh moss substrate. In the degraded peatland, fresh peat at 30 cm showed no mass loss during the incubation period, likely due to the high-water table creating anaerobic conditions. The fresh peat incubated in the intact peatland showed a higher decomposition rate than the same substrate incubated in the degraded peatland due to the comparatively lower water table in the intact peatland. Conclusions Our findings indicate that the quality of the substrate being decomposed and the depth of the water table act as the main factors affecting the decomposition rate in mountain peatlands.

Temperature sensitivity of aerobic and anaerobic organic carbon mineralization varies with climate and soil depth in riparian zones

The temperature sensitivity (Q10) of soil organic carbon (SOC) mineralization plays a vital role in predicting the global carbon cycle under climate change. Q10 has been extensively examined in various terrestrial ecosystems; however, in riparian zones where soil oxygen levels are highly dynamic owing to frequent flooding, Q10 should change with oxygen conditions and show spatial variation, but the mechanisms are still obscure. In this study, we collected topsoil and subsoil samples from riparian zones along a latitudinal gradient and conducted aerobic and anaerobic incubation experiments to determine the latitudinal and vertical patterns of Q10. The results showed that Q10 under anoxic conditions (average of 1.7) significantly exceeded that under oxic conditions (average of 1.4). In general, aerobic SOC mineralization is more sensitive to warming at higher latitudes than at lower latitudes, whereas the pattern is reversed under anoxic conditions. The Q10 in the topsoil was significantly higher than that in the subsoil only under oxic conditions. Metagenomics showed that the abundance of genes involved in the degradation of lignin, carbohydrate esters, and starch in the topsoil increased with latitude, whereas genes for acetate degradation were more abundant in warmer zones, regardless of soil depth. Q10 under oxic conditions was mainly influenced by soil physicochemical properties (e.g., pH and texture), whereas Q10 under anoxic conditions was jointly controlled by climate, soil texture, and acetate degradation genes. Together, anaerobic carbon (C) mineralization in riparian zones is more sensitive to temperature than aerobic metabolism, but the patterns of Q10 under oxic conditions were dependent on both latitude and depth. Our findings highlight that the discrepancies in aerobic and anaerobic C metabolism, and the C cycling process at different soil depths, might play a non-negligible role in affecting the assessment of global C emissions under climate change.

Photothermal conditions and upwelling enhance very short-lived brominated halocarbons emissions in the western tropical Pacific Ocean

Sea-to-air emissions of very short-lived brominated halocarbons (VSLBrHs) are known to contribute to 30 % of stratospheric and tropospheric ozone depletion. However, empirical data on their occurrence in open ocean are scarce, which makes it difficult to estimate the significant contribution of open ocean releases to the global budget of halocarbons. This study was conducted in 2022 to explore the spatial variations of VSLBrHs and their controlling factors in the western tropical Pacific Ocean (WTPO). The findings highlighted that high biological productivity and the resulting dissolved organic matter (DOM) as well as upwelling dynamics significantly influenced the distribution and production of VSLBrHs in seawater, with atmospheric levels primarily governed by oceanic emissions. Based on the simultaneous observation of seawater and atmospheric concentrations, the mean sea-to-air fluxes of CH2Br2, CHBr3, CHBrCl2, and CHBr2Cl were estimated to be 1.01, 6.65, 9.31, and 7.25 nmol m−2 d−1, respectively. Sea-to-air fluxes of these gases in the upwelling regions were 9.0, 4.6, 2.9, and 6.8 times those in the non-upwelling regions, respectively. Additionally, in-situ incubation experiments revealed that the enzymatic mediated biosynthesis pathways of VSLBrHs were enhanced under temperature and light-induced stress and in waters rich in humus-like substances. Therefore, we tentatively concluded that abundant photothermal conditions and the existence of upwelling in the WTPO made it a potential hotspot for the emission of VSLBrHs. This study offers critical insights into the environmental dynamics of VSLBrHs emissions and underscores the importance of regional oceanic conditions in influencing atmospheric greenhouse gas compositions.

Ecotoxicological effects of polyethylene microplastics and lead (Pb) on the biomass, activity, and community diversity of soil microbes

Microplastics and heavy metals are ubiquitous and persistent contaminants that are widely distributed worldwide, yet little is known about the effects of their interaction on soil ecosystems. A soil incubation experiment was conducted to investigate the individual and combined effects of polyethylene microplastics (PE-MPs) and lead (Pb) on soil enzymatic activities, microbial biomass, respiration rate, and community diversity. The results indicate that the presence of PE-MPs notably reduced soil pH and elevated soil Pb bioavailability, potentially exacerbated the combined toxicity on the biogeochemical cycles of soil nutrients, microbial biomass carbon and nitrogen, and the activities of soil urease, sucrase, and alkaline phosphatase. Soil CO2 emissions increased by 7.9% with PE-MPs alone, decreased by 46.3% with single Pb, and reduced by 69.4% with PE-MPs and Pb co-exposure, compared to uncontaminated soils. Specifically, the presence of PE-MPs and Pb, individually and in combination, facilitated the soil metabolic quotient, leading to reduced microbial metabolic efficiency. Moreover, the addition of Pb and PE-MPs modified the composition of the microbial community, leading to the enrichment of specific taxa. Tax4Fun analysis showed the effects of Pb, PE-MPs and their combination on the biogeochemical processes and ecological functions of microbes were mainly by altering amino acid metabolism, carbohydrate metabolism, membrane transport, and signal transduction. These findings offer valuable insights into the ecotoxicological effects of combined PE-MPs and Pb on soil microbial dynamics, reveals key assembly mechanisms and environmental drivers, and highlights the potential threat of MPs and heavy metals to the multifunctionality of soil ecosystems.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, β-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21-2.81 times) in β-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%-45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17-1.59 and 1.18-3.56 times, respectively) under heavy arsenic stress (500mgkg−1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5-50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4-47.9% and 31.2-63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

Carbon and nutrient cycling responses to repeated application of biochar and NPK fertilizers depend on microenvironmental differences among hierarchical aggregate fractions

The conversion of bambara groundnut seed residues into biochar facilitated the bioavailability and retention of more nutrients (C, N, P, K and Mg) after repeated application of biochar. However, the mechanisms of microbially mediated biochar-C degradation and nutrient cycling responses to repeated biochar application, particularly in different hierarchical soil aggregates, are largely unknown. A 20-day incubation experiment was conducted on Ultisols from a 4-year cucumber field trial in Nsukka, Nigeria. The effects of repeated application of bambara seed residue biochar with or without NPK fertilizer on soil aggregate associated electrical conductivity (EC), basal respiration, microbial biomass, and soil enzyme activities were determined. The results showed that the concentration of organic matter in the bulk soils increased with biochar and NPK+biochar treatments. These treatments also increased the soil EC, cumulative CO2 respiration, microbial biomass C and N concentrations, and the activities of tyrosine-aminopeptidase and sulfatase enzymes, compared to the biochar treatment and the control soil. The NPK+biochar treatment contributed 35% more to β-cellobiosidase activity, but the biochar treatment resulted in 85% reduction in N-Acetyl-β-glucosaminidase activity, indicating microbial N mining. The NPK and NPK+biochar treatments accounted for a higher percentage of N-, C and N-, and S- cycle enzyme activities, although their composition was relatively higher with the latter treatment. The overall soil biochemical responses were significantly higher in the micro-aggregates (< 0.25mm) than in the macro-aggregates (≤ 4.75 - 0.25mm); least of all in the small macro-aggregates (0.25 - 1.00mm). Therefore, repeated application of biochar to N-deficient soils generally does not result in positive soil biochemical responses. However, repeated application of biochar together with NPK fertilizer modulates N limitation and optimizes microbial nutrient cycling processes, especially in micro-aggregates.

Phosphorus immobilization/release behavior of lanthanum-modified bentonite amended sediment under the dual effects of pH and dissolved organic carbon

Phosphorus immobilization/release behavior of lanthanum-modified bentonite amended sediment under the dual effects of pH and dissolved organic carbon

Functional role of TrIL-1β in Takifugu rubripes defense against Cryptocaryon irritans infection

The Japanese puffer, Takifugu rubripes, is a commercially important fish species in China that is under serious threat from white spot disease (cyptocaryoniasis), which leads to heavy economic losses. We previously found that interleukin-1β (IL-1β), an important cytokine with a potential role in resistance against pathogens, was one of the most significantly differentially up-regulated proteins in the gills and spleen of T. rubripes infected by the protozoan parasite Cryptocaryon irritans. In this study, we assessed the potential function of T. rubripes IL-1β (TrIL-1β) in fish infected with C. irritans. Phylogenetic analysis indicated that the TrIL-1β protein sequence was most closely related to that of Atlantic salmon (Salmo salar) (67.2 %). The incubation experiments revealed that TrIL-1β may reduce trophont activity by destroying membranes. Immunofluorescence experiments showed that recombinant TrIL-1β promoted the expression of endogenous IL-1β, which penetrated and disrupted the cell membranes of trophonts. Transmission electron microscopy showed that the IL-1β group had less tissue damage compared with control groups of fish. IL-1β-small interfering RNA and IL-1β overexpression experiments were performed in head kidney primary cells, and challenge experiments were performed in vitro. Quantitative RT-PCR results showed that TrIL-1β regulated and activated MyD88/NF-κB and MyD88/MAPK/p38 signaling pathways during C. irritans infection. TrIL-1β also promoted the differential expression of IgM, showing that it was involved in humoral immunity of T. rubripes. The cumulative mortality experiment show that TrIL-1β could protect fish against C. irritans infection. These results enrich current knowledge about the molecular structure of TrIL-1β. They also suggested that recombinant TrIL-1β could be used as an adjuvant in a subunit vaccine against C. irritans infection, which is of profound importance for the prevention and control of parasitic diseases in T. rubripes.

Controlled preparation of bamboo charcoal/BiOCl with efficient visible-light-driven photocatalytic activity for organic pollutant degradation using the residues of bamboo processing

In this research, bamboo charcoal (BC)/BiOCl composites were successfully prepared by a simple hydrothermal method, where the BC was derived from the residues of bamboo processing. The BC/BiOCl composites displayed nanosheet structures with tight combination between bamboo charcoal and BiOCl. The oxygen vacancies (OVs) concentration and photoelectric properties of BC/BiOCl composites were boosted with the doped bamboo charcoal. The photocatalytic performance of the composites was evaluated by the degradation of RhB and TCH. Meanwhile, the possible intermediates, degradation pathways and toxicity of the pollutants in the photocatalytic process were elucidated. When the additive dosage of BC and hydrothermal temperature were 5% and 140°C, the 5BC-140 has highest photocatalytic efficiency under visible light irradiation, and the degradation rates of RhB and TCH over the 5BC-140 composite were 97.9% and 69% at 36 min and 120 min, with the kinetic constants of 6.2 times and 2.0 times as high as those of pure BiOCl, respectively. The establishment of Bi-O-C bonds in the BC/BiOCl played a pivotal role in constructing atomic-level interfacial channels to boost the charge carriers’ separation. The enhanced photocatalytic activity was originated from the robust interaction between bamboo charcoal and BiOCl, promoting the rapid transfer of electrons and suppressing the combination of photogenerated electron-hole pairs through the increased oxygen vacancies. In addition, incubation experiments on green beans demonstrated the nontoxicity of contaminant solution degraded by the BC/BiOCl composites.

Unraveling the Coupled Dynamics between DOM Transformation and Arsenic Mobilization in Aquifer Systems during Microbial Sulfate Reduction: Evidence from Sediment Incubation Experiment

Geogenic arsenic (As)-rich groundwater poses a significant environmental challenge worldwide, yet our understanding of the interplay between dissolved organic matter (DOM) transformation and arsenic mobilization during microbial sulfate reduction remains limited. This study involved microcosm experiments using As-rich aquifer sediments from the Singe Tsangpo River basin (STR) and Jianghan Plain (JHP), respectively. The findings revealed that microbial sulfate reduction remarkably increased arsenic mobilization in both STR and JHP sediments compared to that in unamended sediments. Moreover, the mobilization of As during microbial sulfate reduction coincided with increases in the fluorescence intensity of two humic-like substances, C2 and C3 (R = 0.87/0.87 and R = 0.73/0.66 in the STR and JHP sediments, respectively; p &lt; 0.05), suggesting competitive desorption between DOM and As during incubation. Moreover, the transformations in the DOM molecular characteristics showed significant increases in CHOS molecular and low-O/C-value molecular intensities corresponding to the enhancement of microbial sulfate reduction and the possible occurrence of methanogenesis processes, which suggests a substantial bioproduction contribution to DOM components that is conducive to As mobilization during the microbial sulfate reduction. The present results thus provide new insights into the co-evolution between As mobilization and DOM transformations in alluvial aquifer systems under strong microbial sulfate reduction conditions.

Activated Carbon Application Simultaneously Alleviates Paddy Soil Arsenic Mobilization and Carbon Emission by Decreasing Porewater Dissolved Organic Matter.

Flooding of paddy fields during the rice growing season enhances arsenic (As) mobilization and greenhouse gas (e.g., methane) emissions. In this study, an adsorbent for dissolved organic matter (DOM), namely, activated carbon (AC), was applied to an arsenic-contaminated paddy soil. The capacity for simultaneously alleviating soil carbon emissions and As accumulation in rice grains was explored. Soil microcosm incubations and 2-year pot experimental results indicated that AC amendment significantly decreased porewater DOM, Fe(III) reduction/Fe2+ release, and As release. More importantly, soil carbon dioxide and methane emissions were mitigated in anoxic microcosm incubations. Porewater DOM of pot experiments mainly consisted of humic-like fluorophores with a molecular structure of lignins and tannins, which could mediate microbial reduction of Fe(III) (oxyhydr)oxides. Soil microcosm incubation experiments cospiking with a carbon source and AC further consolidated that DOM electron shuttling and microbial carbon source functions were crucial for soil Fe(III) reduction, thus driving paddy soil As release and carbon emission. Additionally, the application of AC alleviated rice grain dimethylarsenate accumulation over 2 years. Our results highlight the importance of microbial extracellular electron transfer in driving paddy soil anaerobic respiration and decreasing porewater DOM in simultaneously remediating As contamination and mitigating methane emission in paddy fields.

Adaptive strategies of high and low nucleic acid prokaryotes in response to declining resource availability and selective grazing by protozoa

AbstractProkaryotes play a fundamental role in global ocean biogeochemical cycles. However, how the abundance and metabolic activity of ecologically distinct subgroups (i.e., high nucleic acid (HNA) and low nucleic acid (LNA) cells), and their regulating factors, change in response to changing marine environmental conditions remains poorly understood. Here, we delved into the time-evolving dynamic responses of the HNA and LNA prokaryotic subgroups to declining resource availability and selective grazing by protozoa by conducting a 73-day incubation experiment in a large-volume (117,000 L) macrocosm that facilitates community-level exploration. We found that the metabolic activity of the HNA subgroup was higher than that of the LNA subgroup when the macrocosm was resource replete but that the HNA subgroup declined more rapidly than the LNA subgroup as the resources became increasingly scarce, leading to a steadily increasing contribution of LNA cells to prokaryotic activity. Meanwhile, as resources in the macrocosm became limited, protozoan grazing preference shifted from the HNA to the LNA subgroup and the contributions of the LNA subgroup to the carbon flow within the macrocosm increased. The findings highlight the resilience of LNA cells in resource-limited environments, illuminate the critical role of selective grazing by protozoa in balancing distinct prokaryotic subgroups under changing resource conditions, and demonstrate the complex and adaptive interactions between protozoa and prokaryotes across diverse environmental contexts.

Impact of Hood Steaming on Tuber Vitality of Yellow Nutsedge (Cyperus esculentus)

Cyperus esculentus is a hard-to-control, destructive perennial weed propagating and spreading through rhizomes and tubers. Currently, a combination of mechanical, cultural, and chemical measures sustained over time is required for satisfactory control of arable crops. Hood steaming is a promising thermal technique for rapid depletion of the soil tuber bank. The effect of hood steaming on C. esculentus tuber vitality was investigated using a dose–response experiment on two localities in Belgium. Steaming was performed for five durations (2, 4, 8, 16, and 32 min). Moreover, the effects of tuber burial depth (5, 15, and 25 cm), genetic C. esculentus clone (three different clones), and pedohydrological parameters (sandy and sandy, loamy soil) on hood steaming efficacy were determined. Additionally, the heat sensitivity of genetically diverse C. esculentus tubers was investigated in a laboratory incubator experiment in which incubation temperature and duration varied. To control tubers at depths of 5, 15, and 25 cm, treatment durations of 8, 16, and 32 min were required, respectively. In general, clones producing large tubers showed lower heat sensitivity. As pedohydrological parameters may affect heat transfer into the soil, they may affect steaming efficacy as well. To obtain complete control of C. esculentus tubers, soil temperature should be 50 °C or more for at least 42 min. Hood steaming is a highly suitable alternative technique for a rapid and strong depletion of the soil tuber bank in small well-delineated C. esculentus patches.

Response of Soil CO2 Emission to Addition of Biochar and Dissolved Organic Carbon along a Vegetation Restoration Gradient of Subtropical China

Biochar, as a soil amendment, has been widely confirmed to increase soil carbon sequestration. However, how biochar addition affects soil carbon changes during the vegetation restoration process is still unclear, which constrains our ability to explore biochar’s application in the technology of soil carbon sequestration in forests. We conducted an incubation experiment on biochar and dissolved organic matter (DOM) addition to soil at three stages of revegetation (degraded land (DS), plantation forest (PS), and secondary natural forest (NS) in Changting County in Fujian province, China) to investigate the effects of vegetation restoration, biochar, DOM, and their interaction on soil CO2 emission and its relative mechanisms. We found that the accumulative release of CO2-C in the NS and PS soils was 7.6 and 6.8 times higher, respectively, in comparison to that from the DS soil. In the DS, biochar addition significantly increased the accumulative release of CO2-C, soil pH, NH4+-N content, qCO2, phenol oxidase, and peroxidase activities. Peroxidase activities were positively correlated with the accumulative release of CO2-C, and oxidase was the most important direct factor influencing the accumulative release of CO2-C in the DS. However, the accumulative release of CO2-C, soil NH4+-N content, qCO2, β-glucosidase, and N-acetylglucosaminidase activities was significantly reduced after the application of biochar in the PS and NS. These two hydrolases were positively associated with the accumulative release of CO2-C, and hydrolase was the most vital direct factor influencing the accumulative release of CO2-C from the PS and NS soils. The positive effect of DOM addition on CO2 emission under biochar application declined with a vegetation restoration age increase. Our results indicated that biochar could alter microbial physiological processes, inhibit qCO2 and hydrolase activities, and further decrease CO2 emission in relatively fertile soil from the PS and NS; but in the relatively barren soil from the DS, biochar might promote CO2 emission by stimulating microorganisms to enhance qCO2 and oxidase activities.

Effects of Straw Amendment in Combination with Synthetic N Fertilizer Addition on N2O, N2, and Their Stoichiometric Ratios in Three Different Agro-Ecosystems

Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control &lt; KNO3 &lt; rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification.

Pulp mill sludges as a solution for reducing the risk of mineral nitrogen leaching from agriculture

Nitrogen (N) from agricultural systems contributes to the eutrophication of waterbodies through leaching. Incorporating organic material with a high carbon-to-nitrogen (C/N) ratio, such as mixed pulp mill sludges (PMSs), into the soil in autumn could reduce the amount of leachable N. This study tested the potential of composted and lime-stabilised mixed PMSs (CPMS and LPMS) in reducing the concentration of mineral N in the soil, and thus the risk of N leaching from arable land in the boreal region using a two-year field experiment. To better understand the mechanisms of the PMSs for influencing mineral N concentration in soil, the impact of PMSs with different quality on the reactions of N in the soil was investigated in a laboratory incubation study. In the field experiment, nitrate-N (NO3--N) concentration was lower with PMSs compared to mineral fertilisation and the control during the first autumn and the following spring after PMS application. The undersowing of Italian ryegrass reduced the NO3--N concentration in the soil during the first autumn. In the incubation experiment, PMSs reduced the soil ammonium-N (NH4+-N) concentration at the beginning of the experiment and the soil NO3--N concentration throughout the experiment compared to a mineral fertiliser treatment and an organic fertiliser. Increased soil respiration in PMS-treated soils indicated increase in microbial activity, and thus immobilisation of soil NO3--N and NH4+-N due to PMSs addition. These results suggest that PMSs have the potential to reduce N leaching from agricultural soils. However, the immobilisation of N must be considered when planning the nutrient requirements of the following crops.

Impact of liming and maize residues on N2O and N2 fluxes in agricultural soils: an incubation study

AbstractSince it is known that nitrous oxide (N2O) production and consumption pathways are affected by soil pH, optimising the pH of agricultural soils can be an important approach to reduce N2O emissions. Because liming effects on N2O reduction had not been studied under ambient atmosphere and typical bulk density of arable soils, we conducted mesoscale incubation experiments with soils from two liming trials to investigate the impact of long-term pH management and fresh liming on N transformations and N2O production. Soils differed in texture and covered a range of pH levels (3.8–6.7), consisting of non-limed controls, long-term field-limed calcite and dolomite treatments, and freshly limed soils. Both soils were amended with 15N-labelled potassium nitrate (KNO3) and incubated with and without incorporated maize litter. Packed soil mesocosms were cycled through four phases of alternating temperatures and soil moistures for at least 40 days. Emissions of N2O and dinitrogen (N2) as well as the product ratio of denitrification N2O/(N2O + N2), referred to as N2Oi were measured with the 15N gas flux method in N2-reduced atmosphere. Emissions of N2O increased in response to typical denitrifying conditions (high moisture and presence of litter). Increased temperature and soil moisture stimulated microbial activity and triggered denitrification as judged from 15NO3− pool derived N2O + N2 emissions. Fresh liming increased denitrification in the sandy soil up to 3-fold but reduced denitrification in the loamy soil by 80%. N2Oi decreased throughout the incubation in response to fresh liming from 0.5–0.8 to 0.3–0.4, while field-limed soils had smaller N2Oi (0.1–0.3) than unlimed controls (0.9) irrespective of incubation conditions. Our study shows that the denitrification response (i.e., N2O + N2 production) to liming is soil dependent, whereas liming effects on N2Oi are consistent for both long- and short-term pH management. This extends previous results from anoxic slurry incubation studies by showing that soil pH management by liming has a good mitigation potential for agricultural N2O emissions from denitrification under wet conditions outside of cropping season.

Input of high-quality litter reduces soil carbon losses due to priming in a subtropical pine forest

To date, it is unclear how differences in litter quality affect soil organic matter (SOM) decomposition through a phenomenon called 'priming effects' (PEs), especially for low-fertility forest soils under field conditions. Here, the effects of low- and high-quality leaf litter on PE and microbial metabolism of litter-derived carbon (C) were explored in a low-fertility pine (Pinus massoniana) plantation. A 185-day in situ incubation experiment was carried out by adding two 13C-labeled leaf litters to the pine soil—a low-quality (high lignin: nitrogen ratio) litter sourced from pine and a broadleaved species Schima superba produced high-quality (low lignin: nitrogen ratio) litter. To determine the key microbial groups contributing to PEs, the abundance of 13C-labeled litter enrichment in soil phospholipid fatty acids (13C-PLFAs) was quantified. We found that high-quality litter decomposed more rapidly than low-quality litter, with both litter-derived CO2 efflux reaching a plateaued level during the experimental period. Low-quality litter induced net positive PEs, while high-quality litter induced net negative PEs during the litter decomposition processes. The 13C-PLFAs results showed that bacterial groups governed the negative PEs induced by high-quality litter, whereas fungal communities targeted the positive PEs induced by low-quality litter. Random forest model and variation partitioning analysis demonstrated that the direction and magnitude of PEs were driven by litter-induced changes in key microbial groups rather than the structure of the microbial community. Our results demonstrate that microorganisms preferentially utilized litter-derived C in high-quality litter treatment and SOM in low-quality litter treatment, respectively. In contrast to low-quality litter, adding high-quality litter promoted the microbial metabolism of litter-derived C, reducing SOM decomposition (strong negative PEs). Taken together, this study provides isotope-based suggestions for the improvement of degraded pine forests—introducing tree species that produce high-quality litter may benefit soil C sequestration by reducing soil C losses due to PE in nutrient-poor pine forests.