Microbial Respiration Research Articles

Soil dependence of biochar composts in mitigating greenhouse gas emissions: An overlooked biophysical mechanism

Biochar-manure co-compost (BM) has garnered considerable attention as a promising soil amendment for improving nutrient retention and mitigating the emission of greenhouse gases (GHGs). However, its efficacy often varies largely from one soil to another. By comparing soil CO2 and N2O effluxes, solution chemistry, enzyme activities, and the abundances of N-cycle genes between BM and manure compost (M) across three soils of different texture classes through microcosm incubations, we aimed to develop biophysical mechanics to untangle the soil-dependent efficacy of BM in mediating soil carbon and nitrogen transformation processes. Compared to M addition, BM addition significantly reduced soil CO2 and N2O emissions, but its effectiveness was soil texture-dependent, being strongest for CO2 and N2O in fine-textured clay loam and coarse-textured sand, respectively. Such soil texture-dependent effects of BM versus M were also observed in soil enzyme activities and gene copy numbers of ammonia-oxidizing bacteria and denitrifiers. Our datasets suggest that BM interacted strongly with soil texture to modulate the pore scale-based diffusion of oxygen, thereby creating divergence in the aeration status among soils. Sequentially, soil phenol oxidase activity was greater in BM than in M under more aerobic conditions but no difference between BM and M in oxygen-limited soils. The balance between oxygen depletion due to microbial respiration of organic amendments and oxygen diffusion through soil/biochar pores also shaped the activities of nitrifying and denitrifying prokaryotes differently between coarse- and fine-textured soils. This logic model well-explained the magnitude of change in soil-dependent CO2 and N2O emissions from organic amendments. The knowledge gained in this work will likely have profound practical ramifications for optimizing BM efficacy in mitigating the GHGs emission.

Primary study on frass fertilizers from mass-reared insects: Species variation, heat treatment effects, and implications for soil application at laboratory scale

Insect farming has gained popularity as a resource-efficient and eco-friendly method for managing organic wastes by converting them into high-quality protein, fat, and frass. Insect frass is a powerful organic fertilizer that enriches the soil with essential plant nutrients and enhances plant defense mechanisms through chitin stimulation. Given the importance of frass commercialization for many insect farmers and the use of increasingly diverse organic wastes as insect feedstocks, there is a need for legal guidelines to enable clean production practices. The recent introduction of a legal definition for frass and heat treatment requirements by the EU commission marks a significant step towards standardizing its quality; however, little is known about the processes shaping its nutritional profiles and contributing to its maturation. Our study addresses key knowledge gaps in frass composition and production practices. Here, we analyzed the physicochemical, plant-nutritional, and microbiological properties of black soldier fly, yellow mealworm, and Jamaican field cricket frass from mass-rearing operations and assessed the impact of hygienizing heat treatment on fertilizer properties and frass microbiota. The results showed that frass properties varied significantly across insect species, revealing concentrations of plant-available nutrients as high as 7000 μg NH4+-N, 150 μg NO2–NO3--N, and 20 mg available P per g of total solids. Heat treatment reduced microbial activity, biomass, and viable counts of pathogenic Escherichia coli and Salmonella spp. In terms of frass microbiome composition, alpha diversity showed no significant differences between fresh and heat-treated frass samples; however, significant differences in microbial community composition were observed across the three insect species. Despite heat treatment, soil application of frass reactivated and boosted soil microbial activity, inducing up to a 25-fold increase in microbial respiration, suggesting no long-term detrimental effects on microorganisms. These findings not only enhance our understanding of insect frass as a nutrient-rich organic fertilizer but also have implications for regulatory frameworks, underscoring its promising potential for soil health and nutrient cycling. However, it is important to recognize the primary nature of this research, conducted at laboratory scale and over a short term. Future studies should aim to validate these findings in agricultural settings and explore additional factors influencing frass properties and its (long-term) interaction with soil ecosystems.

Soil organic carbon increase via microbial assimilation or soil protection against the priming effect is mediated by the availability of soil N relative to input C

Labile C inputs into soils will be partially transformed into soil organic carbon (SOC) through microbial assimilation or physicochemical protection as such mineral-organic interactions and soil aggregation. The C inputs may stimulate the decomposition of native SOC, inducing a phenomenon known as the priming effect. Increasing C inputs may increase SOC content, yet the relative role of these mechanisms in controlling the magnitudes of SOC increase among soils remains unclear. Four soils differing in microbiology and N content were incubated with 13C-labeled glucose at the amounts of 0.5 (G0.5), 1.0 (G1.0), and 2.0 (G2.0) g C kg−1 soil for 48 days. The objectives of this study were 1) to quantify the fates of added glucose-C, the priming effect, and the changes in SOC and mineral N contents after the incubation, and 2) to identify the main mechanisms for SOC increase with the increased amount of C input and the effects of initial soil N availability and microbial composition. 13C isotope probing showed that 19 to 26 % and 37 to 96 % of added glucose were utilized for microbial respiration and growth, respectively, after the incubation in all soils, with the glucose-C use efficiency ranging from 30 to 60 %. The remaining accounted for 4 to 37 % in all cases except for UltisolHN at G1.0 and G2.0 (–23 % and −2%), which was confirmed as the fraction protected in soil or re-utilized by microbes via acid extraction. The soil-protected glucose-C was higher, while glucose-C use efficiency was lower with the increased amount of added glucose only in the soils with low N. Glucose addition induced a positive priming effect, a SOC increase, and a mineral N loss irrespective of soil type and addition amount. Glucose addition increased the cumulative fungal biomass in all cases and the cumulative bacterial biomass only at G2.0 in all soils and at G1.0 in the high-N soils. It increased the final fungal necromass only at G0.5 in MollisolLN and UltisolHN and at G2.0 in MollisolHN and the final bacterial necromass in all cases except for the low-N soils and UltisolHN at G2.0. With the increased amount of added glucose, the SOC content increased linearly and the priming effect and fungal biomass increased non-linearly, with larger magnitudes in the soils with lower N. These results indicated that glucose was quickly protected after addition and remained in the soil until soil N became a limiting factor for microbial utilization. The availability of soil N relative to input C mediated microbial growth and its controls over SOC change via the soil protection and priming effects. The carbon sequestration potential with increased input of dissolved substrates as such glucose e. g. through root exudation was likely larger in soils with lower fertility due to reduced substrate-C use efficiency and increased effect of soil protection despite an increased priming effect. Further studies are needed on more substrate types as they affect substrate-C use efficiency and soil protection mechanisms.

Divergent responses in microbial metabolic limitations and carbon use efficiency to variably sized polystyrene microplastics in soil

AbstractMicroplastics, considered emerging contaminants, have been accumulating excessively within soil ecosystems, conferring potentially detrimental effects with respect to soil carbon turnover and pools. As a major participant in soil carbon processes, microplastics affecting microorganisms may be one of the main agents affecting soil carbon dynamics. However, the microbial metabolism processes through which microplastics affect soil carbon dynamics remain unclear. Therefore, this study aimed to assess the impact of variously sized (1300, 800, 100, and 0.1 μm) polystyrene microplastics on soil microbial metabolism. Soil microplastics of all sizes invariably and consistently affected microbial metabolism, though nanomicroplastics (0.1 μm) stressed soil microorganisms more than micron‐microplastics. Furthermore, microplastics inhibited both microbial carbon use efficiency (CUE) and respiration, the exception being the CUE in the 1300 μm microplastics treatment. As microplastic particle size decreased, the suppressive influence of microplastics on microbial respiration was gradually lost, the inhibitory effect on microbial CUE increased steadily, and the impact on microorganisms shifted from extracellular to intracellular, with intracellular microplastics exhibiting higher toxicity than extracellular microplastics. We used stoichiometric models to provide precise projections of microbial metabolism features associated with microplastic contamination, thereby enhancing the understanding of the effects of microplastic contamination on the carbon cycle and soil ecosystem.

Mineral protection mediates soil carbon temperature sensitivity of nine old-growth temperate forests across the latitude transect

Temperature sensitivity (Q10) of soil microbial respiration serves as a crucial indicator for assessing the response of soil organic carbon (SOC) to global warming. However, the biogeographic variation in Q10 remains inconsistent. In this study, we examined Q10 and its potential drivers in nine old-growth mixed broad-leaved Korean pine (Pinus koraiensis Sieb. et Zucc.) forests (the climax community of Asian temperate mixed forest) under a wide range of climatic conditions. We found that stand characteristics (arbuscular mycorrhizal tree basal area to ectomycorrhizal tree basal area ratio and root to shoot ratio) contributed to soil C sequestration by facilitating the accumulation of soil recalcitrant C components. Contrary to the C quality-temperature hypothesis, Q10 was not correlated with C quality (soil C to nitrogen ratio and recalcitrant C to labile C ratio). Soil mineral protection parameters (Fe/Al oxides) had negative effect on Q10 because they inhibited microbial activities by decreasing substrate accessibility. Additionally, soils with high microbial biomass C and microbial biomass C to soil organic C ratio had high Q10. Overall, understanding the complex relationships among Q10, mineral protection, and microbial attributes on a spatial scale is essential for accurately predicting soil C cycling in forest ecosystems.

Sustainable indigenous bio-mixture for restoration the soil point source pollution with special reference to chlorpyrifos

Improper pesticide handling is the main cause of contamination of the environment in agricultural systems. This could be caused by leakage of spraying liquid, leftovers, and inappropriate washing of spraying equipment. This study assessed the ability of suggested biomixture modules for remediate repetitive cycles of high chlorpyrifos doses. In three consecutive treatments, four tested modules were contaminated with 160 µg g−1 chlorpyrifos. Chlorpyrifos residues, dehydrogenase activity, and microbial respiration were continuously monitored for 22 weeks. Six bacterial consortia were isolated at the end of the experiment from four treated modules (B+3, BF+3, S+3, and SF+3) and two from untreated modules (B and S). The isolated consortium efficiency in degrading chlorpyrifos was studied. The results revealed that the best chlorpyrifos removal efficiency was achieved when using the stimulated biomixture module (BF) recorded 98%, 100%, and 89%, at the end of three chlorpyrifos treatments, respectively. Such removal efficiency was compatible with the biological activity results of the tested modules: dehydrogenase activity and microbial respiration. There was no difference in the efficiency among the S, B, and BF+3 consortia. The results presented here demonstrate that the combination of vermicompost, wheat straw, soil, and NPK (stimulated biomixture module) can successfully reduce the risk of a point source of pesticide pollution.

How does position affect the decomposition of fine woody debris in subtropical forest?

Fine woody debris (FWD: 1 cm ≤ diameter ≤ 10 cm) may be intercepted by understory vegetation (including the branches of canopy trees). However, the decay dynamics of aerial FWD are often overlooked. In this study, we collected wood from four different tree species (Platycarya strobilacea, Lithocarpus glaber, Pinus massoniana, and Cryptomeria japonica) from four forests in subtropical China, and the mesh bag method was used to measure the remaining mass and microbial respiration by reciprocally transplanting mesh bags filled with different species among the four forests. The main objectives of this study were to reveal the influence of position (the ground and the air) on the decay rates of FWD and the home-field advantage (HFA) effect during a two-year experimental period. Irrespective of the experimental periods and decay fields, the mass loss of FWD was significantly higher on the ground (58.05%) than in the air (45.74%), and the microbial respiration of wood was significantly higher on the ground (18.87 μg CO2 h−1 g−1) than in the air (7.79 μg CO2 h−1 g−1). Microbial respiration was negatively correlated with wood remaining mass on the ground during the entire decay period and in the air only during the late decay period. The HFA effect was observed only on the ground (5.03–23.86%). Our study highlights that soil contact predominantly regulated the decomposition patterns and the HFA effect of fine woody debris and suggests that we should not neglect the decay of fine woody debris in the air due to the interception of understory vegetation in subtropical Chinese forests.

Biogeochemistry of greenhouse gases in coastal upwelling systems: Processes and sensitivity to global change

Major coastal upwelling systems are among the most productive marine ecosystems in the world. They contribute disproportionately to the cycling of carbon and nutrients in the ocean and influence marine biogeochemistry beyond their productive regions. Characterized by intense microbial respiration (both aerobic and anaerobic), major coastal upwelling systems are also hotspots for the production and outgassing of potent greenhouse gases (GHG) such as CO2, N2O, and CH4. Quantifying and understanding these roles in the context of a changing climate is therefore a subject of great interest. Here we provide a short synthesis of the current knowledge of the contributions of major coastal upwelling systems to the cycling of GHG. Despite variations within and among different systems, low-latitude coastal upwelling systems typically act as a net carbon source to the atmosphere, while those at higher latitudes function as weak sinks or remain neutral regarding atmospheric CO2. These systems also significantly contribute to oceanic N2O and CH4 emissions, although the extent of their contribution to the latter remains poorly constrained. We also overview recent and future changes to upwelling systems in the context of a warmer climate and discuss uncertainties and implications for GHG production. Although rapid coastal warming is anticipated in all major coastal upwelling systems, the future changes in upwelling-favorable winds and their implications within the context of increased stratification are uncertain. Finally, we examine the major challenges that impede our ability to accurately predict how major coastal upwelling systems will respond to future climate change, and present recommendations for future research to better capture ongoing changes and disentangle natural and forced variability.

Phytoremediation of pollutants in oil-contaminated soils by Alhagi camelorum: evaluation and modeling

Phytoremediation is a cost-effective and environmentally friendly method, offering a suitable alternative to chemical and physical approaches for the removal of pollutants from soil. This research explored the phytoremediation potential of Alhagi camelorum, a plant species, for total petroleum hydrocarbons (TPHs) and heavy metals (HMs), specifically lead (Pb), chromium (Cr), nickel (Ni), and cadmium (Cd), in oil-contaminated soil. A field-scale study spanning six months was conducted, involving the cultivation of A. camelorum seeds in a nursery and subsequent transplantation of seedlings onto prepared soil plots. Control plots, devoid of any plants, were also incorporated for comparison. Soil samples were analyzed throughout the study period using inductively coupled plasma-optical emission spectroscopy (ICP‒OES) for HMs and gas chromatography‒mass spectrometry (GC‒MS) for TPHs. The results showed that after six months, the average removal percentage was 53.6 ± 2.8% for TPHs and varying percentages observed for the HMs (Pb: 50 ± 2.1%, Cr: 47.6 ± 2.5%, Ni: 48.1 ± 1.6%, and Cd: 45.4 ± 3.5%). The upward trajectory in the population of heterotrophic bacteria and the level of microbial respiration, in contrast to the control plots, suggests that the presence of the plant plays a significant role in promoting soil microbial growth (P < 0.05). Moreover, kinetic rate models were examined to assess the rate of pollutant removal. The coefficient of determination consistently aligned with the first-order kinetic rate model for all the mentioned pollutants (R2 > 0.8). These results collectively suggest that phytoremediation employing A. camelorum can effectively reduce pollutants in oil-contaminated soils.

Divergent regulating modes of greenhouse gas emissions at different soil layers under altered precipitation regime

How soil microbial communities regulate greenhouse gas (GHG) emissions as precipitation events are “repackaged” from many small events to a few larger events has received significant attention. Previous studies have quantified the net fluxes of GHG across the soil/atmosphere interface; however, they have not investigated GHG fluxes in soil profiles under altered precipitation regimes. This study investigated the joint regulation of topsoil and subsoil microorganisms on GHG emissions under changes in precipitation regime in an alpine meadow. Severely altered precipitation regimes have led to changes in NO3–, DOC, and soil moisture among different soil layers, which can be attributed to a combination of substrate migration and changes in carbon and nitrogen mineralization rates. Topsoil microorganisms exhibit high sensitivity to severe changes in the precipitation regime, which can affect their biomass, microbial composition, and metabolic activities. In contrast, the activity of subsoil microorganisms remains relatively stable. This was likely due to the heterogeneity of dominant regulators across soil layers. Under the severely altered precipitation regime, carbon dioxide (CO2) emissions significantly decreased by approximately 11.08%. This decrease was primarily due to a reduction in microbial respiration in the topsoil. The decrease in both topsoil and subsoil methane (CH4) uptake likely caused the inhibition of the CH4 sink from the surface (by approximately 11.60%). While a 1.75-fold increase in nitrous oxide (N2O) emissions under the severe changes in the precipitation regime might be primarily related to the increase in subsoil N2O emissions caused by the increasing abundance of subsoil denitrifiers, as well as the addition of subsoil nitrate content and soil moisture. This study revealed the divergent modes of microbial communities at different soil layers regulating GHG fluxes, which could guide the improvement of ecological models predicting GHG emissions in response to altered precipitation regimes.

Nonsignificant elevational trends of soil microbial respiration and temperature sensitivity in a subtropical forest

AbstractSoil carbon (C) cycling plays a critical role in regulating global C budget and atmospheric CO2 concentrations. The ongoing global warming potentially accelerates soil C loss induced by microbial respiration (MR) and makes soil a large C source to the atmosphere. Quantifying the drivers of MR and its response to rising temperature (also called temperature sensitivity, Q10) should be a high priority to improve the modeling and prediction of terrestrial C cycle under global warming. In this study, we applied a standardized soil sampling along nine gradients from 410 to 1080 m in a subtropical forest in southern China. All soil samples were incubated at varying temperature gradients (10–15–20–25–20–15°C) to measure MR and Q10 every day for three weeks. Then all the measured MR was adjusted by the field temperature of each elevation gradient. Our objectives were to examine the response of MR and Q10 to the environmental change induced by elevational gradients in the subtropical forest and then quantify their main drivers. We totally collected 54 abiotic and biotic factors relative to the MR and Q10. Our results showed that the incubated MR increased from low to high elevation. However, a significant elevation trend of the adjusted MR was not examined after adjusting the field temperature of sampling sites, due to the trade‐off between increasing soil C concentration and declining temperature as elevation increased. We further found that the elevational gradients did not cause significant change in Q10. The variation in Q10 was negatively dominated by soil C quality, which declined nonlinearly along the elevation gradients. This study highlights the trade‐off between environment and biotic factors in determining soil C decomposition along elevational gradients. The uncertainty of MR measurements caused by unifying incubated temperature should not be ignored in future model development.

Rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance with the change of land use types.

Soil microorganisms play an important role in soil ecosystems as the main decomposers of carbon and nitrogen. They have an indispensable impact on soil health, and any alterations in the levels of organic carbon and inorganic nitrogen can significantly affect soil chemical properties and microbial community composition. Previous studies have focused on the effects of carbon and nitrogen addition on a single type of soil, but the response of soil microorganisms to varying carbon and nitrogen inputs under different land soil use types have been relatively understudied, leaving a gap in our understanding of the key influencing factors. To address this gap, we conducted a study in the tropical regions of Hainan province, focusing on four distinct land use types: natural forest soil (NS), healthy banana soil (HS), diseased banana garden soil (DS), and paddy soil (PS). Within each of these environments, we implemented five treatments: CK, RS (rice straw), RSN (rice straw and NH4NO3), RR (rice root), and RRN (rice root and NH4NO3). Our aim was to investigate how soil bacteria response to changes in carbon and nitrogen inputs, and to assess their potential for biological nitrogen fixation. The results showed that the addition of rice straw increased the absorption and utilization of nitrate nitrogen by microorganisms. The addition of rice roots (RR) did not increase the absorption capacity of inorganic nitrogen by microorganisms, but increased the content of poorly soluble organic carbon. Most importantly, the addition of rice straw increased microbial respiration and the utilization efficiency of N2 by microorganisms, and the further addition of ammonium nitrate increased microbial respiration intensity. With the change of soil type, the rice straw increases microbial nitrogen fixation, bacterial and nifH genes abundance. Meanwhile, microbial respiration intensity is an important factor influencing the differences in the structure of bacterial communities. The addition of inorganic nitrogen resulted in ammonium nitrogen accumulation, reduced microbial richness and diversity, consequently diminishing the soil microorganisms to resist the environment. Therefore, we believe that with the change of soil types, corresponding soil nutrient retention strategies should be devised and incorporated while reducing the application of ammonium nitrogen, thus ensuring healthy soil development.

Metal uptake from iron ore mine tailings by perennial ryegrass (Lolium perenne L.) is higher after wheat straw than wheat straw biochar amendment

Background and aimsMine tailings often contain high concentrations of metals that may lead to serious environmental concerns. Phytoremediation by suitable plant species, coupled with organic amendments, represents an intriguing way of improving the quality of mine tailings.MethodologyWe conducted a glasshouse pot study to assess the impact of biochar derived from wheat straw (BC) and wheat straw (WS) at different application rates (w/w: 0%, 1%, 2%, 5%, 10%) in enhancing physicochemical and biological attributes of iron ore mine tailings. Perennial ryegrass (Lolium perenne L.) growth and uptake of metals (Co, Cu, Fe, Mn, Zn, Cr, Ni, Pb) and As were assessed.ResultsThe pH(H2O) of iron mine tailings (6.62 with 0% amendment) significantly increased to 8.01 in BC 10% but decreased to 5.33 in WS 10%. However, electrical conductivity, total carbon, total nitrogen and cation exchange capacity increased significantly with application of either amendment. Improvement in physicochemical parameters of tailings by amending with WS was associated with significantly greater plant growth compared with BC amendment. Shoot As and Pb accumulation by perennial ryegrass was low (below detection limit), whereas that of Co, Cu, Fe, Mn, Zn, Cr and Ni increased with an increase in both BC and WS application. Microbial biomass carbon and respiration were enhanced more in the WS than in BC treatments.ConclusionThis study suggests wheat straw is a better amendment than biochar for the iron ore mine tailings.

Eddy‐Mediated Turbulent Mixing of Oxygen in the Equatorial Pacific

AbstractIn the tropical Pacific, weak ventilation and intense microbial respiration at depth give rise to a low dissolved oxygen (O2) environment that is thought to be ventilated primarily by the equatorial current system (ECS). The role of mesoscale eddies and vertical mixing as potential pathways of O2 supply in this region, however, remains poorly known due to sparse observations and coarse model resolution. Using an eddy resolving simulation of ocean circulation and biogeochemistry, we assess the contribution of these processes to the O2 budget balance and find that vertical mixing of O2, which is modulated by the surface wind speed and the vertical shear of the eddying currents, contributes substantially to the replenishment of O2 in the upper equatorial Pacific thermocline, complementing the advective supply of O2 by the ECS and meridional circulation at depth. These transport processes vary seasonally in conjunction with the wind: mixing of O2 into the upper thermocline is strongest during boreal summer and fall when the vertical shear and eddy kinetic energy are intensified. The relationship between eddy activity and the downward mixing of O2 arises from the modulation of equatorial turbulence by Tropical Instability Waves via their impacts on the vertical shear. This interaction of processes across scales sustains a local pathway of O2 delivery into the equatorial Pacific interior and highlights the need for adequate observations and models of turbulent mixing and mesoscale processes for understanding and predicting the fate of the tropical Pacific O2 content in a warmer and more stratified ocean.

Erosion of community complexity increases temperature-dependency of microbial respiration, but not growth, in short-term incubations

Biodiversity loss and climate change are 2 of the most alarming threats to ecosystem functioning and stability. These factors are, however, typically investigated separately, overlooking potential interactions between species extinctions and climate change on ecosystems. Here, we evaluated how different temperature regimes impact the relationship between microbial diversity and ecosystem functioning, in terms of temperature sensitivity of carbon (C) cycling functions. We hypothesized that more complex communities promote the stability of C cycling functions under both temperature regimes. We did not observe a ubiquitous response of all C-cycling processes to temperature increases within communities of distinct complexities. While growth was stable with increasing temperatures across the complexity levels, respiration rates increased more strongly at low complexity than high complexity levels at higher temperatures. Carbon use efficiency, which integrates both growth and respiration, tended to decrease with temperature at lower levels of complexity. Jointly, these results demonstrate the importance of community complexity for maintaining C-cycling thermal response under a changing climate.

Metabolic Rates of Rainbow Trout Eggs in Reconstructed Salmonid Egg Pockets

In situ evaluations of the metabolic rates (i.e., respiration and excretion) of salmonid eggs are mostly indirect, focusing on the sampling of hyporheic water from wild or artificial nests. Comparatively, experimental studies carried out under controlled, laboratory conditions are less abundant due to methodological difficulties. This study presents a novel experimental setup aimed to address this issue and enable the measurement of oxygen and dissolved inorganic nitrogen fluxes in simulated rainbow trout (O. mykiss) egg pockets. The experimental setup consists of reconstructed egg pockets in cylindrical cores under flow-through conditions. Live and dead eyed-stage eggs were incubated in a natural, sterilised gravel substrate. Hyporheic water circulation was ensured using peristaltic pumps, with the possibility to collect and analyse inflowing and outflowing water for chemical analyses. Microcosm incubations, with closed respirometry of eggs in water alone, were also carried out in order to infer the importance of microbial respiration in the simulated egg pockets. The results show an increasing trend in oxygen demand, due to the development of biofilm in the reconstructed egg pockets and increased egg respiration rates. Moreover, egg pockets showed positive ammonium net fluxes connected with the advancing developmental egg stage, while nitrate removal peaked during the last phase of the experiment, mainly due to the formation of oxic-hypoxic interfaces, leading to couple nitrification–denitrification processes. The suggested approach enables to test a number of in situ situations, including the effects of extreme hydrological conditions, sediment clogging and sudden changes in water chemistry or temperature on the survival and metabolic performances of nests, at different egg development stages.

Long-term organic amendments increase the vulnerability of microbial respiration to environmental changes: Evidence from field and laboratory studies

Organic amendments can improve soil fertility and microbial diversity, making agroecosystems more resilient to stress. However, it is uncertain whether organic amendments will enhance the functional capacity of soil microbial communities, thereby mitigating fluctuations in microbial respiration caused by environmental changes. Here, we examined the impacts of long-term organic amendments on the dynamics of microbial catabolic capacity (characterized by enzyme activities and carbon source utilization) and microbial respiration, as well as their interrelationships during a period with fluctuating temperature and rainfall in the field. We then subjected the field soil samples to laboratory heating disturbances to further evaluate the importance of microbial catabolic capacity in explaining patterns of microbial respiration. In both field and laboratory experiments, organic amendments tended to increase the stability of microbial catabolic capacity, but significantly increased the vulnerability of microbial respiration to environmental changes. However, the direction and driving factors of microbial respiration affected by environmental changes differed between the field and laboratory experiments. Environmental changes in the field suppressed the promotional effects of organic amendments on microbial respiration mainly through reducing microbial catabolic capacity, while laboratory heating further enhanced microbial respiration mainly due to increased soil resource availability. Together, these findings suggest that increased microbial respiration variations under organic amendments may potentially increase the uncertainty in predicting soil carbon emissions in the scenario of ongoing climate/anthropogenic changes, and highlight the necessity of linking laboratory studies on environmental changes to field conditions.

Changes in the cellulolytic activity and microbial respiration of soils of different types under conditions of contamination with heavy metals

It has been experimentally established that when soils are polluted with heavy metals, the boundary concentrations of metals above which signs of ecotoxicity are detected are different for the microbial community. Inhibition of respiration of the studied soils was observed at lower doses of Pb, Zn and Cd than enzymatic cellulase activity. Cd compounds and polyelement contamination conditions are the most toxic for microorganisms. Concentrations of heavy metals have been identified that can have a significant negative impact on the soil microbial community at different levels of contamination of sod-podzolic, gray forest, leached chernozem and chestnut soils. In descending order of resistance to TM, the studied soils can be arranged in the following row: leached chernozem (Luvic Chernozem) grey forest (Eutric Retisol (Ochric)) chestnut (Haplic Kastanozem) ≥ sod-podzolic (Eutric Albic Retisol (Ochric)).

Land leveling and cover cropping impacts on chemical and biological properties of paddy soil

Aim of study: To examine the impact of solitary land leveling and its combination with cover cropping on the chemical and biological characteristics of paddy soil. Area of study: This research focused on paddy fields located in Guilan Province, situated in northern Iran. Specifically, two sites were chosen for investigation, where land leveling had been conducted 5 years and 2 years prior to this study, respectively. Furthermore, cover cropping was implemented during the second year after the latter area's land leveling. Material and methods: A total of 80 composite soil samples were collected, with 20 samples gathered from both leveled and unleveled plots at the designated study sites. Various soil chemical and biological properties such as organic carbon, total nitrogen, available phosphorus, exchangeable potassium, microbial respiration, and biomass carbon were quantified. Subsequently, a paired t-test was employed to analyze the impact of land leveling and the combined effects of land leveling with cover cropping on soil attributes. Main results: The study revealed that five years after land leveling, there was a significant decrease in organic carbon, total nitrogen, microbial respiration, and biomass carbon. In contrast, the area leveled and cover cropped for two years exhibited higher levels of these attributes compared to adjacent unleveled parcels. Research highlights: This study highlights the distinct effects that solitary land leveling and land leveling combined with sustainable practices like cover cropping have on soil attributes.

Synergistic Control of Trimethoprim and the Antimicrobial Resistome in Electrogenic Microbial Communities.

Synergistic control of the risks posed by emerging antimicrobials and antibiotic resistance genes (ARGs) is crucial for ensuring ecological safety. Although electrogenic respiration can enhance the biodegradation of several antimicrobials and reduce ARGs accumulation, the association mechanisms of antimicrobial biodegradation (trimethoprim, TMP) with the fate of the antimicrobial resistome remain unclear. Here, the biotransformation pathway of TMP, microbial associations, and functional gene profiles (e.g., degradation, antimicrobial resistance, and electron transfer) were analyzed. The results showed that the microbial electrogenic respiration significantly enhanced the biodegradation of TMP, especially with a cosubstrate sodium acetate supply. Electroactive bacteria enriched in the electrode biofilm positively correlated with potential TMP degraders dominated in the planktonic communities. These cross-niche microbial associations may contribute to the accelerated catabolism of TMP and extracellular electron transfer. Importantly, the evolution and dissemination of overall ARGs and mobile genetic elements (MGEs) were significantly weakened due to the enhanced cometabolic biodegradation of TMP. This study provides a promising strategy for the synergistic control of the water ecological risks of antimicrobials and their resistome, while also highlighting new insights into the association of antimicrobial biodegradation with the evolution of the resistome in an electrically integrated biological process.