Laboratory Incubation Experiment Research Articles

Effects of Organic Amendments and Mineral Fertilizers on Optimizing Nutrient Cycling in Alkaline Soil

Soil microbial biomass carbon (MBC) and nitrogen (MBN) are indicators of microbial size and soil fertility, representing a vital living nutrient reservoir in the soil. This study aimed to evaluate the impact of various organic sources, such as poultry manure (PM), farmyard manure (FYM), compost (CM), and biochar (BC), along with different levels of mineral fertilizers on soil microbial dynamics and nutrient (N, P) mineralization through laboratory incubation experiments. The organic amendments were applied at rates of 0.25%, 0.5%, and 1.0% of soil carbon (w/w), combined with 75%, 50%, and 25% of recommended doses of NPK (120:90 and 60 kg N, P2O5, and K2O ha-1), respectively. Following the application of amendments, the soil underwent a 16-day incubation period to measure CO2 emissions and a 28-day period for N and P mineralization. The rate of CO2 evolution exhibited a significant increase with higher carbon levels but declined over time. Compost showed the highest CO2 evolution at any given time, followed by PM, FYM, and BC, likely due to a higher readily available fraction of carbon. Compost, particularly at the 1% C level in combination with inorganic fertilizer, led to a significant increase in soil microbial biomass C and N. Nitrogen and phosphorous mineralization increased with the duration of the 28-day incubation period. However, the net release of N and P decreased with higher carbon levels, potentially associated with both immobilization and the fact that higher levels received lower (25%) NPK levels. Nevertheless, soils treated with CM and PM maintained higher levels of N and P, associated with their higher fraction of labile nutrients. These findings suggest that the continuous application of organic sources enhances N and P mineralization, soil microbial biomass, and their activity. Therefore, the regular application of carbon sources emerges as a strategic approach to improving the soil health of less fertile alkaline calcareous soils.

Biogenic emission as a potential source of atmospheric aromatic hydrocarbons: Insights from a cyanobacterial bloom-occurring eutrophic lake

As important precursors of ozone (O3) and secondary organic aerosol (SOA), reactive aromatic hydrocarbons (AHs) have typically been classified as anthropogenic air pollutants. However, biogenic emission can also be a potential source of atmospheric AHs. Herein, field observations in a eutrophic lake were combined with laboratory incubation experiments to investigate the biogenic AH emission. Field work showed that the water-air fluxes of AHs measured at sites with high cyanobacteria abundance could reach an order of magnitude greater than those at sites with low cyanobacteria abundance, suggesting that cyanobacteria could be the important contributor to measured AHs. Laboratory incubation experiments further confirmed the AH emission of cyanobacteria and revealed that the emission could change significantly over the lifespan of cyanobacteria and varied to their growing conditions. By combining field observations and laboratory incubation experiments, it has been suggested that the emission of different AH species from cyanobacteria could be modulated by variable biogeochemical mechanisms and that the biochemical process of toluene could be different from that of other AHs. This study investigates AH emissions from inland aquatic ecosystem and suggests that biogenic emission could be a potential source of atmospheric AHs.

Effect of Organic Amendments on the Speciation of Chromium in Contaminated and Uncontaminated Soils

ABSTRACT Quantitative speciation of metals and their variability over time is a critical concept in environmental soil chemistry. Chromium is a heavy metal that has negative effects on the environment and human health. There have been several attempts to study the behavior of chromium in soils and its removal from soil. However, there is relatively little knowledge about the immobilization of chromium and its chemical speciation in contaminated and uncontaminated soils when different organic amendments are applied. A laboratory incubation experiment was conducted in a completely randomized design to evaluate the effect of organic amendments on the speciation of chromium in contaminated and uncontaminated soils. Four organic amendments were used: farmyard manure (FYM), rice straw compost (RSC), vermicompost (VC), and biochar (BC). Each of them was applied at 1% to contaminated as well as uncontaminated soils. In both the amended and unamended soils, chromate (CrO4 2-), bichromate (HCrO4 −), and calcium chromate (CaCrO4) in soil-water system followed the order CrO4 2-> HCrO4 −> CaCrO4. The application of FYM, RSC, VC, and BC significantly decreased the CrO4 2- and CaCrO4 in the soil-water system of both soils. However, only the application of BC affected the HCrO4 − contaminated soils. In both soils, HCrO4 − exists as the predominant chromium species in the pH range of 2.0 to 6.25. At pH 6.25, CrO4 2- and HCrO4 − each contribute 50% of the total dissolved chromium in soil solution. CrO4 2- dominated in the system as the pH increased from 6.25 till 8.0. The maximum concentration of CrO4 2- was at pH 8.0. At pH <3.0, CrO3SO4 2- contributes less than 10%. Overall, organic amendments decreased the concentration of Cr species in both soils. However, the decrease in concentration was highly dependent on the nature of the amendment applied. Therefore, organic amendments can be exploited to remediate chromium-contaminated soils.

Effects of Land-Use Type and Salinity on Soil Carbon Mineralization in Coastal Areas of Northern Jiangsu Province

Sea level rise due to glacier melting caused by climate warming is a major global challenge, but the mechanism of the effect of salinity on soil carbon (C) mineralization in different land types is not clear. The pathways by which salinity indirectly affects soil carbon mineralization rates need to be investigated. Whether or not the response mode is consistent among different land-use types, as well as the intrinsic links and interactions between soil microbial resource limitation, environmental stress, microbial extracellular enzyme activity, and soil carbon mineralization, remain to be demonstrated. In this paper, three typical land-use types (wetland, forest, and agroforestry) were selected, and different salinity levels (0‰, 3‰, 6‰, and 32‰) were designed to conduct a 125-day laboratory incubation experiment to determine the soil CO2 release rate, soil physicochemical properties, and soil enzyme activities, and to correlate C mineralization with biotic and abiotic factors. A correlation analysis of soil physical and chemical properties, extracellular enzyme activities, and carbon mineralization rates was conducted to investigate their intrinsic linkages, and a multiple linear regression of C mineralization at different sites was performed to explore the variability of mineralization among different site types. Structural equation models were established in the pre- and post-incubation stages to study the pathways of soil C mineralization at different incubation times, and the mechanism of mineralization was further verified by enzyme stoichiometry. The results showed that, at the end of 125 days of incubation, the 32‰ salinity addition reduced the cumulative mineralization of forest and agroforestry types by 28.41% and 34.35%, respectively, compared to the 0‰ salinity addition. Soil C mineralization in the three different land-use types was highly correlated with the active C fractions of readily oxidizable C (ROC), dissolved organic C, and microbial biomass C (MBC) in the soil, with the standardized coefficients of multivariate linear regression reaching 0.67 for MBC in the wetland and −0.843 for ROC in the forest. Under long-term salinity additions, increased salinity would reduce the microbial respiratory quotient value by inhibiting β-glucosidase activity, thus indirectly affecting the rate of CO2 release. With added salinity, the mineralization of non-saline soil was more susceptible to the inhibitory effect of salinity, whereas the mineralization of salinized soil was more controlled by soil C pools.

Effect of bioremediation or organic treatments of soil contaminated with some heavy metals on the biological and L- glutaminase activity

For the purpose of identify the ability of bioremediation or organic treatments of soil to reduce the harmful effect of heavy metals including Zn, pb and cd on the biological activity such as soil respiration, the total number of fungi and the activity of the L-glutaminase enzyme have been studied. A laboratory incubation experiment was applied in the Soil Microbiology Laboratory in the Department of Soil Sciences and Water Resources in the College of Agriculture– Basrah University. The soil of the surface layer (0-30 cm) from Qurna district, north of Basrah province was contaminated with the critical levels of the heavy metals cd, Pb, Zn and were placed in an incubator at 30°C for 14 days. The biological and organic treatments process was applied by inoculating soil contaminated with Aspergillus niger or humic acid (40 L ha-1) or sterilized cow manure (4%), incubated at 25°C for 30 days, then some biological parameters were estimated at the periods of 10, 20 and 30 days. Results have been showed that an inhibitory effect of the studied heavy metals on the biological parameters, and the Cd has been recorded the highest percentage of inhibition of total number of fungi (30.67%), the amount of CO2 released (13.93%) and the activity of the L-glutaminase enzyme (45.33%) compared to the control treatment. The ability of the treatments materials to remove heavy metals were (89.02%) for A. niger compared to humic acid (63.48%) and cow manure (48.71%). It was reflected in an increase in the number of fungi, which recorded 152, 167.75, 174.5 cfu g-1 when treated with A. niger, cow manure and humic acid, respectively compared to the control treatment which was (65.92 cfu g-1). The biological and organic treatments also increased the level of liberated CO2 from the polluted soil to 268.62, 253.86, 303.59 mg CO2 g-1, respectively compared to the control treatment. The activity of the L-glutaminase enzyme has increased due to application of treatments. It was 57.02, 48.97, 70.41 µg NH4+ g-1 2hr.-1 for inoculated with A. niger or treated with cow manure and humic acid, respectively, while the control treatment was 37.19 µg NH4+ g-12hr.-1.

Short-term effect of liquid organic fertilisation and application methods on N2, N2O and CO2 fluxes from a silt loam arable soil

AbstractThe absence of N2 flux measurements in liquid manure-amended soils has resulted in a poor understanding of the effect of manure application on gaseous N losses. The aim of this study was to quantify N2, N2O, CO2, N2O reduction to N2, depth distribution of moisture, water-extractable organic C, NO3−, NH4+, pH, and diffusivity in a laboratory incubation experiment with an arable silt-loam soil. To quantify N processes and gaseous fluxes, 15N tracing was applied. An artificial livestock slurry-mixture was added to the soil in various treatments (control, surface or injected application; slurry-application rate: 42.9 kg N ha− 1; soil water content of either 40% or 60% water-filled pore space (WFPS)). The soil was incubated for 10 days. The depth distribution of the control parameters was measured twice during the experiment on days 5 and 10. The average increase in N2 and N2O fluxes from denitrification was about 900% in slurry-amended soils. The highest N2 and N2O fluxes from denitrification were measured in the slurry injection, 60% WFPS treatment (7.83 ± 3.50 and 11.22 ± 7.60 mg N m− 2 d− 1, respectively). The hypothesis that injected slurry at a higher water content enhances denitrification was confirmed. This study provides important insights into the formation, spatial and temporal variation of the manure-soil hotspot and its impact on the denitrification process. The results will form part of a dataset to develop, improve and test manure application submodules of biogeochemical models and will help to understand in detail the effect of hotspots on N-cycling in manure-treated soils.

Effects of biobased fertilisers on soil physical, chemical and biological indicators – a one-year incubation study

Soil quality is declining in Europe and globally due to agricultural practices and climate change. The European market for novel biobased fertilisers (BBFs) is growing and the new European Union fertiliser regulation promotes their use. However, knowledge about the effects of many novel BBFs on soil quality is currently very limited. In a one-year laboratory incubation experiment, this study aimed to test the effect on biological (microbial biomass carbon (C)), physical (clay dispersibility and water-holding capacity) and chemical (pH, cation exchange capacity (CEC), total C and C in soil size fractions (&lt;250, 50–250 and &gt;50 μm)) soil quality indicators of 10 BBFs applied at two different rates on two soil types: an Arenosol and a Luvisol. The set-up also included a soil that was subjected to long-term annual application of the compost used in the incubation. The application of BBFs generally improved soil quality, with the compost material improving soil quality most, followed by a plant-based fertiliser and a biogas digestate. The effect of BBF application on CEC, total C and particulate organic matter (POM) was related to the amount of total C added with the BBF. Furthermore, the effect on total C and POM fractions was also related to easily decomposable C added with the BBF. Comparing the single accelerated application with annual application under field conditions indicated that the long-term incubation trial is a reasonable predictor of compost long-term effects in the field. Whether this applies to BBFs with very different properties remains to be shown.

Investigating organic sulfur in estuarine and offshore environments: A combined field and cultivation approach

Estuarine-offshore sediments accumulate substantial particulate organic matter, containing organic sulfur as a key component. However, the distribution and sources of organic sulfur in such environments remain poorly understood. This study investigated organic sulfur in the Yangtze River Estuary and adjacent East China Sea. Dissolved organic sulfur varied from 0.65 to 1.99 μmol/L (molar S:C 0.006–0.018), while particulate organic sulfur ranged from 0.42 to 2.69 μmol/L (molar S:C 0.007–0.082). Sedimentary organic sulfur exhibited a similar molar S:C ratio (0.014–0.071) to particulate organic sulfur in bottom water, implying that particulate matter deposition is a potential source. Furthermore, sediments exposed to frequent hypoxia harbored significantly higher organic sulfur and S:C values compared to non-hypoxic areas. Laboratory incubation experiments revealed the underlying mechanism: sustained activity of sulfate-reducing bacteria in hypoxic sediments led to a substantial increase in sedimentary organic sulfur (from 15 to 53 μmol/g) within 600 days. This microbially driven sulfurization rendered over 90 % of the organic sulfur resistant to acid hydrolysis. Therefore, this study demonstrates that, alongside particle deposition, microbial sulfurization significantly contributes to organic sulfur enrichment and likely promotes organic matter preservation in estuarine-offshore sediments, particularly under hypoxic conditions. This finding advances our understanding of organic sulfur sources in these vital ecosystems.

Differential degradation dynamics of λ-cyhalothrin in mineral and peat soils: a comparative study under laboratory condition

Dissipation kinetics of λ-cyhalothrin in mineral and peat soils of Semongok (mineral soil) and Sibu (peat soil) farms was investigated in a laboratory incubation experiment under different temperature and moisture conditions at normal and double application dosages. The soil was spiked with λ-cyhalothrin at 5 and 25 µg/g soil, respectively. The soil moisture content was adjusted to 20, 40, and 60% of field capacity and then incubated in three climatic chambers at 15, 25, and 35 °C. Samples were collected at 0, 7, 21, 42, 70, and 105 days and analysed by Gas Chromatography-Electron Capture Detector (GC-ECD). Pesticides from the soil were extracted via a facile-modified QuEChERS method. Recovery studies of λ-cyhalothrin in mineral and peat soils were carried out at 0.05, 0.1, 0.5 and 1.0 µg/g fortification levels. The percentage of recovered amount was in the range of 81.4–95.0% and 81.3–86.5% for mineral and peat soils, respectively which falls within the acceptable recovery range of 70.0–120.0%. Factors i.e., soil carbon content, moisture, temperature, and applied dosage that render the degradation of λ-cyhalothrin in mineral and peat soils were evaluated. Findings showed that faster λ-cyhalothrin degradation took place in soil that contained low organic carbon content (< 12%), low soil moisture (≤ 20%) and incubated under higher temperatures (≤ 35 °C). Degradation of λ-cyhalothrin was described by first-order kinetics in both mineral and peat soils at various conditions. Half-lives of λ-cyhalothrin in mineral soil were shorter compared to peat soil. This is due to its lower carbon content and lower soil organic matter availability. This study provides significant information to the agriculture industry and farmers on the important factors such as soil properties, environmental conditions and application dosage that will influence the fate of pesticides in soil.Graphical abstract

Biochar produced at high temperature mitigates N2O emission and promotes nitrogen retention in subtropical forest soils

AbstractBiochar is produced by burning biomass under oxygen‐limited conditions, and it has been widely used as a soil amendment to improve soil functions such as nutrient retention. However, whether the impact of biochar application on soil nitrogen (N) transformation and N2O emission varies with the pyrolysis temperature remains unclear, especially in different forest types in subtropical regions. In this study, a 60‐day laboratory incubation experiment was conducted to evaluate the impact of biochar with different pyrolysis temperatures (300°C [BC300], 500°C [BC500], and 800°C [BC800]) on net N transformation rates and N2O emission in soils collected from Castanopsis kawakamii dominated natural forest (NF) and Chinese fir (Cunninghamia lanceolate, CF) plantation in subtropical China. The results showed that the application of biochar significantly increased soil ammonium (NH4+) content (p &lt; 0.001) but reduced nitrate (NO3−) content (p &lt; 0.001) compared with the control. The soil NH4+ content of the BC800 treatment was significantly higher than that of other treatments (p &lt; 0.001). Biochar application significantly reduced soil net N mineralization (NRmin) and nitrification (NRnit) rate (p &lt; 0.001), but increased net ammonification (NRamm) rate (p &lt; 0.001). The application of biochar led to a remarkable decrease in cumulative N2O emission compared to the control (p &lt; 0.001). In particular, soils treated with high‐temperature biochar emitted significantly lower N2O compared to other treatments (p &lt; 0.001). The partial least squares path model demonstrated that biochar influenced N2O emission through a direct effect in NF soil and an indirect effect in CF soil. This study highlights the distinct role of biochar, particularly that produced under high pyrolysis temperatures as a soil amendment to mitigate N2O emission and promote N retention in both subtropical natural and planted forests.

Degradation of atrazine, glyphosate, and 2,4-D in soils collected from two contrasting crop rotations in Southwest Chaco, Argentina

Argentina stands as one of the leading consumers of herbicides. In a laboratory incubation experiment, the persistence and production of degradation metabolites of Atrazine, 2,4-D, and Glyphosate were investigated in a loamy clay soil under two contrasting agricultural practices: continuous soybean cultivation (T1) and intensified rotations with grasses and legumes (T2). The soils were collected from a long-term no-till trial replicating the influence of the meteorological conditions in the productive region. The soil was enriched with diluted concentrations of 6.71, 9.95, and 24 mg a.i./kg-1 of soil for the respective herbicides, equivalent to annual doses commonly used in the productive region. Samples were taken at intervals of 0, 0.5, 1, 2, 4, 6, 8, 16, 32, and 64 days, and analysis was conducted using high-resolution liquid chromatography UPLC MS/MS. An optimal fit to the first-order kinetic model was observed for each herbicide in both rotations, resulting in relatively short half-lives. Intensified crop sequences favored the production of biotic degradation metabolites. The impact of the high frequency of soybean cultivation revealed a trend of soil acidification and a reduced biological contribution to attenuation processes in soil contamination.

Study in a long-term laboratory experiment of the potential susceptibility to mineralization of organic matter in post-agrogenic light gray soils

Relevance. Since 2021, work has begun in Russia to assess the fertility of unused arable land and its involvement in agricultural circulation. Changes in the farming system of post-agrogenic soils can lead to uncontrolled mineralization of newly formed soil organic matter (SOM) under fallow vegetation and significant CO2 emissions into the atmosphere. Studies of the nature of SOM accumulation under fallow vegetation and assessment of its potential susceptibility to mineralization are relevant, since they can become the basis for the development of agrotechnical methods for returning unused lands to arable circulation with the maximum preservation of their fertility.Methods. In a long-term laboratory incubation experiment, we studied the dynamics of changes in the intensity of basal (BR) and substrate-induced respiration (SIR) in postagrogenic soils to assess the potential susceptibility to SOM mineralization with a change in land use. Layered samples (0–10 and 10–20 cm) were used from the old arable horizons of two fallow plots with different humus conditions. The results of the incubation experiment were compared with the results of assessing the quantitative content and qualitative composition of SOM.Results. In the 0–10 cm layer, the respiration rates are higher than in the 10–20 cm layer. The results of the assessment of the respiration intensity are consistent with the assessment of the qualitative composition of SOM. The accumulation of SOM occurs mainly in the upper part of postagrogenic soils due to mobile easily oxidized organic compounds of a fulvic nature. When developing agrotechnical methods for returning fallow lands to arable circulation, it is necessary to focus primarily on basic processing technologies that ensure maximum preservation of potentially easily mineralized material accumulated in the upper layer.

The ability of soils to aggregate, more than the state of aggregation, promotes protected soil organic matter formation

Efforts to increase soil organic carbon (SOC) are pursued as a viable climate change mitigation strategy. Boosting SOC stocks requires increasing plant carbon (C) inputs and promoting their persistence in SOC. In well aerated mineral soils, water soluble inputs are expected to stabilize through chemical binding to minerals, forming mineral-associated organic carbon (MAOC) before or after microbial transformation, while structural inputs are expected to stabilize as particulate organic carbon (POC) via protection in soil aggregates. Although ample research is centered on the effects of soil aggregation, its disturbance (e.g., tillage), and microbial processing on SOC cycling, we still lack mechanistic understanding of how plant C input type (i.e., soluble versus structural) and disturbance (i.e., aggregate disruption) independently and in interaction affect POC and MAOC formation and stabilization in soils with inherently different degrees of aggregation.To this end, using 13C enriched structural and soluble plant inputs, we traced SOC formation and stabilization in a lab incubation experiment in soils with differing levels of aggregation, and capacity to form aggregates after disturbance. Our results showed that soluble plant inputs contributed substantially to MAOC and that higher formation and persistence of MAOC occurred in the highly aggregated soil. Moreover, the highly aggregated soil retained more soluble inputs stabilized as MAOC when disturbed. Disturbance in this fine textured, organic carbon rich soil stimulated regeneration of aggregates around structural plant inputs leading to greater persistence of aggregate-occluded POC. Soluble plant inputs, specifically, as well as structural plant inputs in the highly aggregated disturbed soil, compensated for SOC lost due to disturbance alone.Overall, this study provides mechanistic evidence suggesting that management strategies for SOC accrual should consider soil type, aggregation potential, and plant attributes to inform decisions surrounding tillage frequency and cropping regimes. Our mechanistic findings require testing. If confirmed in the field, they would suggest that no disturbance in tandem with high structural plant C inputs would benefit most SOC accrual in systems with soils that have little capacity to form organo-mineral complexes, including large aggregates. On the contrary, with sustained plant inputs, occasional disturbance in systems with soils that have a high capacity to form organo-mineral complexes can promote both POC and MAOC formation and stabilization.

Evaluation of Biochar and Inorganic Fertilizer on Soil Available Phosphorus and Bacterial Community Dynamics in Acidic Paddy Soils for Different Incubation Temperatures

The composition of microbial communities and the functioning of ecosystems are greatly influenced by the nutrient inputs. Despite this fact, our knowledge regarding the impact of phosphorus (P) inputs on soil P availability and microbial community structures in subtropical acidic soils remains limited. We hypothesized that diverse P inputs, incubation temperatures, and soil types could significantly alter soil P availability and microbial communities. To address this gap, we conducted a laboratory incubation experiment, investigating the effects of biochar and inorganic P amendments on soil available P, soil pH, acid phosphatase enzymes, and bacterial abundance. We employed two different incubation temperatures (15 °C and 25 °C) using acidic paddy soil and red soil from the subtropical Southern China region. Our results indicate a notable increase in soil pH, reaching 37% and 39% at 15 °C and 40% and 40.6% at 25 °C, respectively, following the application of biochar and inorganic P amendments in paddy soil. In the case of red soil, we observed pH increases of 41% and 43% at 15 °C and 44% and 45% at 25 °C after the application of biochar and inorganic P amendment, respectively. The addition of inorganic P amendment resulted in the highest available P contents in paddy soil, reaching 111.47 mg/kg at 15 °C and 100.17 mg/kg at 25 °C, respectively. However, Proteobacteria decreased after inorganic P addition, which showed that P might not be the only limiting nutrient for various bacterial communities. Bacterial diversity and richness indices were found to be higher after biochar application in both soils. Gemmatimonadetes, Acidobacteria, and Actinobacteria were found to be strongly influenced by incubation temperatures, whereas most of the top abundant bacterial phyla, such as Gemmatimonadetes, Actinobacteria, Chloroflexi, Acidobacteria, Planctomycetes, Firmicutes, Patescibacteria, and Bacteroidetes, were highly dependent on soil type. At the genus level, various important P solubilizing genera (Pseudomonas, Bradyrhizobium, Streptomyces jietaisiensis, Massilia) significantly increased after biochar and inorganic P addition in both soils. The correlation analysis proved that P-solubilizing genera were significantly associated with changes in soil pH, as well as soil available P after biochar and inorganic P addition. Conclusively, in a short-term incubation experiment, inorganic P amendment greatly increased the soil pH and available phosphorus contents compared to biochar and control treatments; however, the microbial community was observed to be strongly associated with biochar application, soil type, and incubation temperature.

Elevated temperature and nutrients lead to increased N2O emissions from salt marsh soils from cold and warm climates

Salt marshes can attenuate nutrient pollution and store large amounts of ‘blue carbon’ in their soils, however, the value of sequestered carbon may be partially offset by nitrous oxide (N2O) emissions. Global climate and land use changes result in higher temperatures and inputs of reactive nitrogen (Nr) into coastal zones. Here, we investigated the combined effects of elevated temperature (ambient + 5℃) and Nr (double ambient concentrations) on nitrogen processing in marsh soils from two climatic regions (Quebec, Canada and Louisiana, U.S.) with two vegetation types, Sporobolus alterniflorus (= Spartina alterniflora) and Sporobolus pumilus (= Spartina patens), using 24-h laboratory incubation experiments. Potential N2O fluxes increased from minor sinks to major sources following elevated treatments across all four marsh sites. One day of potential N2O emissions under elevated treatments (representing either long-term sea surface warming or short-term ocean heatwaves effects on coastal marsh soil temperatures alongside pulses of N loading) offset 15–60% of the potential annual ambient N2O sink, depending on marsh site and vegetation type. Rates of potential denitrification were generally higher in high latitude than in low latitude marsh soils under ambient treatments, with low ratios of N2O:N2 indicating complete denitrification in high latitude marsh soils. Under elevated temperature and Nr treatments, potential denitrification was lower in high latitude soil but higher in low latitude soil as compared to ambient conditions, with incomplete denitrification observed except in Louisiana S. pumilus. Overall, our findings suggest that a combined increase in temperature and Nr has the potential to reduce salt marsh greenhouse gas (GHG) sinks under future global change scenarios.

Non-linear effects of temperature and moisture on gross N transformation rates in an Inner Mongolian grassland

Understanding how soil nitrogen (N) turnover responds to temperature and soil moisture alterations is important for accurately predicting responses of soil N availability and plant productivity to global climate change. However, few studies had explored such questions under natural conditions. We investigated effects of temperature and moisture on soil gross N turnover with an annual scale field experiment in an Inner Mongolian grassland and a laboratory incubation experiment. In the field experiment, on the annual scale both gross ammonification and nitrification rates showed a hump-shaped response to temperature, with maximum rates occurring around 10 °C and 5 °C, respectively. Gross ammonification rates did not respond to soil moisture, and gross nitrification rates decreased first and then increasing with soil moisture, which the threshold was 35% water holding capacity (WHC). Totally, soil temperature explained more variation than moisture in gross ammonification (0.30 VS 0.04) and nitrification (0.24 VS 0.14) rates. On the seasonal scale, both soil temperature and moisture showed generally significant effects on gross N turnover. Grazing had no effects on soil temperature and moisture sensitivity of gross N turnover on the annual scale, but increased the sensitivity of gross ammonification to soil moisture during the spring freeze–thaw period. In the laboratory incubation experiment, gross ammonification and nitrification rates increased with the increase of temperature, although there was no difference between 20 °C and 30 °C. Gross ammonification rates reached a maximum at 50% WHC, while gross nitrification rates did not respond to soil moisture until 100% WHC. Soil temperature explained more variation than moisture in gross ammonification (0.71 VS 0.01) and nitrification (0.37 VS 0.25) rates. Our results imply that climate warming may have greater impact on gross nitrogen turnover compared to changes in rainfall, however it remains great uncertainty due to the low explanation of soil temperature and moisture.

Dynamics of soil nitrogen availability following conversion of natural forests to various coffee cropping systems in northern Thailand

Land conversion critically affects soil physiochemical and biological properties, yet very little remains clear about the impact of forest conversion on the N pool and related microbial N transformations. Therefore, this study aimed to examine the dynamics of soil N availability following forest conversion into the different coffee cropping systems, and explore the mechanisms behind these dynamics from the microbial N transformation. Disturbed soil samples from two depths (0–20 and 20–40 cm) were collected from four land uses consisting of three different coffee cropping systems (coffee monocultures (C), coffee agroforestry (FC), coffee associated with persimmon (Diospyros kaki L.) (CH)) converted from natural forest and adjacent natural forest (F) in northern Thailand. The soil labile N pools (including ammonium (NH4+), nitrate (NO3−), inorganic N (IN), dissolved organic N (DON) contents and microbial biomass N (MBN)) were measured, as well as the soil total N (STN) content. Soil N transformation rates, including net N mineralization, nitrification, and immobilization, were determined using a laboratory incubation experiment. The results showed that the forest conversion to coffee agroforestry significantly increased soil N content by 39.83 % in topsoil, but no significant difference was observed in C and CH soils as compared to F soil (p ≤ 0.05). The three labile N forms (NH4+, NO3− and DON content) were significantly higher under the C, FC and CH soils in both depths, while the coffee monoculture decreased the MBN content. The increases in soil IN, IN/DON and NO3−/NH4+ ratios used as an N availability indicator were positively associated with an increase in the N mineralization and nitrification processes following the forest conversion. Interestingly, the N immobilization processes in the F and FC soils were significantly higher than those in the C and CH soils, which indirectly regulated a decreased nitrification rate in F and FC soils in our study. With the exception of the FC soil, the nitrification/N immobilization ratios in the C (4.95) and CH (4.08) soils were higher than those in the F (0.70) soil, indicating an increased N loss risk after forest conversion. Therefore, coffee agroforestry systems have the potential to be effective management strategies for improving soil nitrogen sequestration following forest conversion.

Effects of microplastics on cold seep sediment prokaryotic communities

Cold seep sediments are an important reservoir of microplastics (MPs) whose impact on the structure and function of prokaryotic community is not well understood. In this study, the impact of 0.2% and 1% (w/w) polyethylene (PE), polystyrene (PS), and polypropylene (PP) MPs on the cold seep sediment prokaryotic community was investigated in a 120-day laboratory incubation experiment. The results revealed that exposure to MPs altered sedimentary chemical properties in a type- and concentration-dependent manner. Furthermore, MPs significantly altered the structure of bacterial community, with some MPs degradation-associated bacterial phyla significantly increasing (p < 0.05). However, in the case of archaea, the changes in the structure of microbial community were less pronounced (p > 0.05). Co-occurrence network analysis revealed that the addition of MPs reduced the network complexity, while PICRUSt2 and FAPROTAX analyses suggested that 0.2% PP and 1% PS MPs had the most significant effects on the nitrogen and carbon cycles (p < 0.05). Overall, this study provides new insights into the effects of MPs on the structure and function of microbial communities in cold seep sediments.

Local Beneficial Microorganisms Impact Carbon and Nitrogen Mineralization in a Lixisol Incubated with Organic Waste Products

Growing awareness of the environmental impact of intensive agriculture has prompted a quest for more sustainable approaches. The most promising alternatives include the application of organic waste products (OWPs), as well as biofertilizers containing local beneficial microorganisms (BMs) on cultivated soils. This study was designed to assess the effects of BMs on carbon and nitrogen mineralization of OWPs. A 28-day laboratory incubation experiment was conducted at 28 °C with a soil, three OWPs (poultry litter (PL), cow dung (CD), and sewage sludge (SS)), and three BMs (groundnut + millet from Saint-Louis (LGM), groundnut from the southern groundnut basin (BG), and rice from the southern groundnut basin (BR) in Senegal), alone and combined. The results showed that the C mineralization from OWP + BM + soil mixtures exceeded (range 13–41%) those measured for OWP + soil. The BM input induced an increase or reduction in OWP nitrogen mineralization, depending on the type of BM and OWP. However, the net mineral nitrogen (Nmin) obtained with the PL-LGM and SS-BG combinations was 13.6- and 1.7-fold higher than with PL and SS, respectively, at 28 days. The addition of BM seemed to lead to a decrease in the C: N ratio, an improvement in the availability of nitrogen, and an increase in microbial activity in the OWP + BM + soil mixture. Our results generated new information on the variation patterns of OWP carbon and nitrogen in OWP-BM-soil systems. This novel insight will be developed to guide the most appropriate choice of OWP-BM mixtures for improved fertilization in sustainable production systems.

Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric CO2 levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments. These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Findings reveal that the addition of calcite increased the benthic alkalinity release from 0.4 μmol cm−2 d−1 (control) to 1.4 μmol cm−2 d−1 (calcite) as well as other weathering products such as calcium. However, these enhanced fluxes returned to lower fluxes after approximately 4 weeks yet still higher than the un-amended controls. Microbial activity appeared to be the primary driver for lowering pore water pH and thus enhanced weathering. In several sediment cores, pH profiles taken at the start of the experiments indicated activity of sulfur oxidizing Beggiatoa spp, which was verified by RNA-profiling of 16S rRNA genes. The pH profiles transitioned to those commonly associated with the activity of cable bacteria as the experiments progressed. The metabolic activity of cable bacteria would explain the significantly lower pH values (~5.6) at sediment depths of 1–3 cm, which would favor substantial calcite dissolution. However, a high abundance of cable bacteria was not reflected in 16S rRNA sequence data. Total alkalinity (TA) fluxes in these cores increased by a factor of ~3, with excess TA/calcium ratios indicating that the enhanced flux originated from calcite dissolution. The dissolution of dunite or the potential formation of secondary minerals could not be identified due to the strong natural flux of silicic acid, likely due to biogenic silica dissolution. Furthermore, no accumulation of potentially harmful metals such as nickel was observed, as highlighted as a potential risk in other studies concerning OAE. Given the complexity of sediment chemistry and changes of the benthic conditions induced by the incubation, it remains challenging to distinguish between natural and enhanced mineral weathering. Further investigation, including the identification of suitable tracers for mineral dissolution, are necessary to assess the feasibility of benthic weathering as a practical approach for OAE and climate change mitigation.