Decrease In Microbial Biomass Research Articles

Nitrogen addition enhances nitrogen but not carbon mineralization in aggregate size fractions of soils in a Pinus massonia plantation

IntroductionAtmospheric nitrogen (N) deposition can impact the levels of soil organic carbon (SOC) and total nitrogen (total N) by altering the soil N availability. However, the effect of N input on the mineralization of SOC and total N in various soil aggregate size fractions requires further clarification.MethodsThe soil samples were collected from a Pinus massoniana plantation situated in the Three Gorges Reservoir Area of China. Over a period of three years, the soils from the plantation were subjected to four different levels of nitrogen addition (0 [N0], 30 [N30], 60 [N60], and 90 [N90] kg N ha−1 yr−1). The impact of N addition on the mineralization of SOC and total N in aggregates was evaluated through an incubation experiment, encompassing four aggregate sizes (2000 − 8000, 1000 − 2000, 250 − 1000, and < 250 μm).ResultsThe < 250 μm fraction showed the highest levels of cumulative C mineralization, while the lowest levels were observed in the 2000 − 8000 μm fraction. Compared to the < 250 um fraction, a drop of 9 − 21% in cumulative C mineralization was observed in the 2000 − 8000 μm fraction, indicating that soil aggregates enhance the stability of C in the soil. Cumulative N mineralization levels were consistently at their lowest in the 2000 − 8000 μm fraction, indicating aggregates reducing mineralization-related N loss. Adding N to forest soil samples led to a reduction in cumulative C mineralization. In contrast, an opposite trend was observed in the cumulative N mineralization after adding N in microaggregates. Nitrification was the main contributor to net N mineralization. SOC and total levels increased in response to N30 and N60. N addition leads to an increase in the weight ratio of the 1000 − 2000 μm fraction. Moreover, N90 was linked to decreases in microbial biomass C and N.DiscussionThese findings confirm that the structural characteristics of soil aggregates play a crucial role in sequestering organic carbon and total N sequestration in the presence of N deposition, while highlighting N loss from the soil caused by N input.

Nitrogen deposition suppresses soil respiration by reducing global belowground activity

Soil respiration (Rs) indicates below-ground biological activities. Previous studies have suggested that higher nitrogen (N) deposition due to human activities exerts an increasingly negative effect on Rs. However, the mechanisms underlying this negative effect remain highly uncertain on a global scale. Using a global dataset of 262 N addition experiments, here we show the overall N addition effects on Rs changed from positive to negative with increasing N addition rate and duration. By constructing a structural equation model (SEM) that explained 41 % variation in the responses of Rs to N addition, we revealed that Rs under increasing N addition was simultaneously associated with decreases in soil pH, root biomass and microbial biomass, with the strongest influence by root biomass. Decreasing soil pH had cascading effects on root and microbial biomass, while N-addition-induced root biomass reduction further manifested a decrease in microbial biomass. Across global variations in the environment, lower background soil pH amplified the negative impacts of N addition on root and microbial biomass, which consequently exhilarated the negative impact of high N on Rs. Our results highlight that predicting the response of belowground biological activities to global changes is complex with the essence of integrative understanding for the multivariate pathways through soil physical properties, plants and microorganisms.

Global patterns of the interactive effects of N and P enrichment on terrestrial microbial biomass

Nitrogen (N) and phosphorus (P) are key components in biogeochemical cycling and considerable efforts have been made to understand the effects of their availability on microbial biomass. Nevertheless, the interplay between N and P supply in modulating soil microbes remains unclear. We conducted a comprehensive global analysis of 108 studies spanning boreal to tropical regions to evaluate their interactive impacts on microbial biomass. The findings revealed a significant decrease in microbial biomass with N addition, whereas P supplementation resulted in a notable increase in microbial biomass. Among the observed interactive effects, additive effects were predominant. More importantly, we found that among all of the assessed factors, the impacts of N-P interaction on soil microorganisms are dependent on changes in soil pH. In conclusion, our findings provide valuable insights into the interactive effects of N and P enrichment on microbial biomass. These findings will contribute to the development of global models that predict the impacts of N and P enrichment on soil microbes and ecosystem functions.

Land Use Change from Natural Tropical Forests to Managed Ecosystems Reduces Gross Nitrogen Production Rates and Increases the Soil Microbial Nitrogen Limitation.

Understanding the underlying mechanisms of soil microbial nitrogen (N) utilization under land use change is critical to evaluating soil N availability or limitation and its environmental consequences. A combination of soil gross N production and ecoenzymatic stoichiometry provides a promising avenue for nutrient limitation assessment in soil microbial metabolism. Gross N production via 15N tracing and ecoenzymatic stoichiometry through the vector and threshold element ratio (Vector-TER) model were quantified to evaluate the soil microbial N limitation in response to land use changes. We used tropical soil samples from a natural forest ecosystem and three managed ecosystems (paddy, rubber, and eucalyptus sites). Soil extracellular enzyme activities were significantly lower in managed ecosystems than in a natural forest. The Vector-TER model results indicated microbial carbon (C) and N limitations in the natural forest soil, and land use change from the natural forest to managed ecosystems increased the soil microbial N limitation. The soil microbial N limitation was positively related to gross N mineralization (GNM) and nitrification (GN) rates. The decrease in microbial biomass C and N as well as hydrolyzable ammonium N in managed ecosystems led to the decrease in N-acquiring enzymes, inhibiting GNM and GN rates and ultimately increasing the microbial N limitation. Soil GNM was also positively correlated with leucine aminopeptidase and β-N-acetylglucosaminidase. The results highlight that converting tropical natural forests to managed ecosystems can increase the soil microbial N limitation through reducing the soil microbial biomass and gross N production.

Long-term warming-induced trophic downgrading in the soil microbial food web

Climatic warming has been hypothesized to accelerate organic matter decomposition by soil microorganisms and thereby enhance carbon (C) release to the atmosphere. However, the long-term consequences of soil warming on belowground biota interactions are poorly understood. Here we investigate how geothermal warming by 6 °C for more than 50 years affects soil microbiota. Using metatranscriptomics we obtained comprehensive profiles of the prokaryotic, eukaryotic and viral players of the soil microbial food web. When compared to ambient soil temperature conditions, we found pronounced differences in taxa abundances within and between trophic modules of the soil food web. Specifically, we observed a ‘trophic downgrading’ at elevated temperature, with soil fauna decreasing in abundance, while predatory bacteria and viruses became relatively more abundant. We propose that the drivers for this shift are previously observed decreases in microbial biomass and soil organic carbon, and the increase in soil bulk density (decrease in soil porosity) at elevated temperature. We conclude that a trophic downgrading may have important implications for soil carbon sequestration and nutrient dynamics in a warming world.

Assessing the Fate of Superparamagnetic Iron Oxide Nanoparticles Carrying Usnic Acid as Chemical Cargo on the Soil Microbial Community.

In the present study we evaluate the effect of superparamagnetic iron oxide nanoparticles (SPIONs) carrying usnic acid (UA) as chemical cargo on the soil microbial community in a dystrophic red latosol (oxysol). Herein, 500 ppm UA or SPIONs-framework carrying UA were diluted in sterile ultrapure deionized water and applied by hand sprayer on the top of the soil. The experiment was conducted in a growth chamber at 25 °C, with a relative humidity of 80% and a 16 h/8 h light-dark cycle (600 lx light intensity) for 30 days. Sterile ultrapure deionized water was used as the negative control; uncapped and oleic acid (OA) capped SPIONs were also tested to assess their potential effects. Magnetic nanostructures were synthesized by a coprecipitation method and characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), zeta potential, hydrodynamic diameter, magnetic measurements, and release kinetics of chemical cargo. Uncapped and OA-capped SPIONs did not significantly affect soil microbial community. Our results showed an impairment in the soil microbial community exposed to free UA, leading to a general decrease in negative effects on soil-based parameters when bioactive was loaded into the nanoscale magnetic carrier. Besides, compared to control, the free UA caused a significant decrease in microbial biomass C (39%), on the activity of acid protease (59%), and acid phosphatase (23%) enzymes, respectively. Free UA also reduced eukaryotic 18S rRNA gene abundance, suggesting a major impact on fungi. Our findings indicate that SPIONs as bioherbicide nanocarriers can reduce the negative impacts on soil. Therefore, nanoenabled biocides may improve agricultural productivity, which is important for food security due to the need of increasing food production.

Response of soil organic carbon decomposition to intensified water variability co-determined by the microbial community and aggregate changes in a temperate grassland soil of northern China

The effect of precipitation variability on soil organic carbon (SOC) decomposition is vital in regulating the global carbon (C) cycle and climate change. However, the response of SOC decomposition to different magnitudes of precipitation variability and its dependence on moisture level are still controversial. In this study, we conducted a three-month incubation experiment that manipulated soil water levels and the intensity of water variability with a homogenized topsoil from a temperate grassland. Results showed that intensified water variability significantly reduced CO2 emissions at the low-water level, but did not affect the SOC decomposition at the high-water level. Meanwhile, the microbial community was significantly altered by the intensified water variability, showing a decrease in microbial biomass and increases in the fungi: bacterial ratio and Gram-positive: Gram-negative bacteria ratio, which tended to suppress the SOC decomposition. However, the intensified water variability significantly stimulated the breakdown of macro-aggregates to micro-aggregates at the high-water level, which promoted the substrate availability in soil and compensated for the suppressed SOC decomposition by microbial community responses. The findings highlight that the response of SOC decomposition to intensified water variability is co-determined by the microbial community responses and aggregate instabilities.

How interactions between wildfire and seasonal soil moisture fluxes drive nitrogen cycling in Northern Sierra Nevada forests

As wildfires become larger and more severe across western North America, it grows increasingly important to understand how they will affect the biogeochemical processes influencing ecosystem recovery. Soil nitrogen (N) cycling is a key process constraining recovery rates. In addition to its direct responses to fire, N cycling can also respond to other post-fire transformations, including increases or decreases in microbial biomass, soil moisture, and pH. To examine the short-term effects of wildfire on belowground processes in the northern Sierra Nevada, we collected soil samples along a gradient from unburned to high fire severity over 10 months following a wildfire. This included immediate pre- and post-fire sampling for many variables at most sites. While season and soil moisture did not substantially alter pH, microbial biomass, net N mineralisation, and nitrification in unburned locations, they interacted with burn severity in complex ways to constrain N cycling after fire. In areas that burned, pH increased (at least initially) after fire, and there were non-monotonic changes in microbial biomass. Net N mineralisation also had variable responses to wetting in burned locations. These changes suggest burn severity and precipitation patterns can interact to alter N cycling rates following fire.

Changes in the nutrient dynamics and microbiological properties of grape marc in a continuous-feeding vermicomposting system.

Finding strategies to reuse and treat organic wastes is of utmost need. Biological processes offer the possibility to transform them into safer end products with benefits for both agriculture and the environment. Moreover, it represents an ecologically-sound and economically attractive alternative to landfill disposal and incineration. In this work, we evaluated the feasibility of vermicomposting to treat and process grape marc, the main solid by-product of the wine industry. The long-term changes in grape marc derived from both white and red winemaking processes were assessed throughout the process of vermicomposting from a physico-chemical and microbiological perspective. New layers of fresh marc were added sequentially in the presence and absence of earthworms (Eisenia andrei) forming an age gradient during a 42-week period. An optimal moisture level of 70% was maintained over the course of the process. The pH fell within weak-alkaline levels through the layerś profile and the electrical conductivity was between 200 and 300 µS cm-1, providing optimum conditions for earthworm growth. The mass loss caused by earthworm activity led to an increased content of macro- and micronutrients at the end of the trial. An overall decrease in microbial biomass and its activity, indicative of a stabilised material, was also recorded with depth of layer. Altogether, this points to vermicomposting as a suitable management system for processing grape marc with a dual purpose, that is fertilizer production and environment protection. This is especially relevant in the current attempts to reach a fully circular economy.

Enhanced plant leaf P and unchanged soil P stocks after a quarter century of warming in the arctic tundra

AbstractPhosphorus (P) limits or co‐limits plant and microbial life in multiple ecosystems, including the arctic tundra. Although current global carbon (C) models focus on the coupling between soil nitrogen (N) and C, ecosystem P response to climate warming may also influence the global C cycle. Permafrost soils may see enhanced or reduced P availability under climate warming through multiple mechanisms including changing litter inputs through plant community change, changing plant–microbial dynamics, altered rates of mineralization of soil organic P through increased microbial activity, and newly exposed mineral‐bound P via deeper thaw. We investigated the effect of long‐term warming on plant leaf, multiple soil and microbial C, N, and P pools, and microbial extracellular enzyme activities, in Alaskan tundra plots underlain by permafrost. Here, we show that 25 yr of experimental summer warming increases community‐level plant leaf P through changing community composition to favour relatively P‐rich plant species. However, despite associated increases in P‐rich litter inputs, we found only a few responses in the belowground pools of P available for plant and microbial uptake, including a weak positive response for citric acid–extractable PO4 in the surface soil, a decrease in microbial biomass P, and no change in soil P (or C or N) stocks. This weak, neutral, or negative belowground P response to warming despite enhanced litter P inputs is consistent with a growing number of studies in the arctic tundra that find no long‐term response of soil C and N stocks to warming.

Does a decrease in microbial biomass alter mycorrhizal attributes and soil quality indicators in coal mining areas under revegetation process?

Losses of microbial diversity in degraded ecosystems still have obscure consequences, especially when considering the interaction between arbuscular mycorrhizal fungi (AMF) and soil bacteria. This study investigates the effect of decreasing microbial biomass on mycorrhizal attributes and soil quality indicators. The dilution-to-extinction approach was applied in microcosms to search for associations among bacterial diversity, mycorrhizal attributes, and soil quality indicators. The experiment was conducted with four soil treatments (undiluted control 100 = D0, 10−3 = D3, 10−6 = D6, and 10−9 = D9) from a short-term (two years = 2Y) and a long-term (15 years = 15Y) coal mine revegetation area. Microcosms were inoculated with 300 spores of Acaulospora colombiana, Gigaspora albida, and Claroideoglomus etunicatum with millet as the host plant. Results included the total number of AMF spores, mycorrhizal colonization, soil aggregation, glomalin, fluorescein diacetate hydrolysis (FDA), basal soil respiration, microbial biomass, and soil bacterial microbiome. Larger differences were observed between areas than between dilution treatments within the sampling area. Attributes that presented differences in the dilutions compared to D0 2Y samples were mycorrhizal colonization (D0 = 85% and D9 = 43.3%), FDA (D0 = 77.2% and D9 = 55.5%), extractable glomalin-related soil protein (D0 = 0.09 and D9 = 0.11) and bacterial diversity (D0 = 7.3 and D6 = 5.3). D0 15Y samples presented differences in microbial biomass nitrogen (D0: 232.0) and bacterial diversity (D0: 7.9, D9: 5.6) compared to the dilutions. Bacterial microbiome present in the D0 samples formed distinct clusters as to other samples and correlated with soil aggregation and basal respiration attributes. Results suggest that AMF inoculation and dilution-to-extinction did not affect soil quality indicators preeminently, but the bacterial community is affected and can influence the process of environmental revegetation. A long-term revegetation period is substantial to improve quality indicators and establish the diversity of microorganisms and consequently revegetation in areas impacted by coal mining.

Evidence for microbial rather than aggregate origin of substrates fueling freeze-thaw induced N2O emissions

Soil freeze-thaw induces a pulse of nitrous oxide (N2O) emissions fueled by a concomitant increase in available organic carbon (C) and nitrogen (N) substrates. These substrates are hypothesized to originate from the disruption of aggregates and microbial biomass, but experiments designed to falsify these hypotheses have been scarce. We therefore conducted a series of column experiments using intact soil cores of silt loam and loamy sand under different freezing rates and durations, factors previously identified as controlling the magnitude of subsequent N2O emissions. We used a slower freezing rate and shorter freeze duration (6 days) as a Control, to which we compared the same freeze duration but faster freezing rate (Fast, 6 days) and the same freezing rate but longer freeze duration (Long, 21 days). All soils were frozen to ~ -2.5 °C. Upon thaw, only the silt loam emitted N2O; we therefore focused on silt loam C, N, and aggregate dynamics. Control and Fast soils emitted similar amounts of N2O, even though Fast soils maintained aggregate mean weight diameter (MWD). Long soils emitted 1.8 times more N2O than Control, even though Long and Control soils exhibited similar decreases in aggregate MWD. We suggest that because in no instance were differences in N2O emissions between treatments proportional to differences in aggregate disruption, and some soils emitted N2O without any detectable aggregate disruption, that aggregate disruption does not play a significant, universal role in providing substrates for N2O emissions. In contrast, larger N2O emissions due to longer freezing durations were associated with a delayed decrease in microbial biomass. Although we did not assess microbial communities for features other than their biomass, our observations are consistent with longer freezing durations selecting for slower growing microorganisms and freeze-thaw induced N2O emissions being fueled by microbial osmolytes.

Discovering the potential of an nZVI-biochar composite as a material for the nanobioremediation of chlorinated solvents in groundwater: Degradation efficiency and effect on resident microorganisms

Abiotic and biotic remediation of chlorinated ethenes (CEs) in groundwater from a real contaminated site was studied using biochar-based composites containing nanoscale zero-valent iron (nZVI/BC) and natural resident microbes/specific CE degraders supported by a whey addition. The material represented by the biochar matrix decorated by isolated iron nanoparticles or their aggregates, along with the added whey, was capable of a stepwise dechlorination of CEs. The tested materials (nZVI/BC and BC) were able to decrease the original TCE concentration by 99% in 30 days. Nevertheless, regarding the transformation products, it was clear that biotic as well as abiotic transformation mechanisms were involved in the transformation process when nonchlorinated volatiles (i.e., methane, ethane, ethene, and acetylene) were detected after the application of nZVI/BC and nZVI/BC with whey. The whey addition caused a massive increase in bacterial biomass in the groundwater samples (monitored by 16S rRNA sequencing and qPCR) that corresponded with the transformation of trichloro- and dichloro-CEs, and this process was accompanied by the formation of less chlorinated products. Moreover, the biostimulation step also eliminated the adverse effect caused by nZVI/BC (decrease in microbial biomass after nZVI/BC addition). The nZVI/BC material or its aging products, and probably together with vinyl chloride-respiring bacteria, were able to continue the further reductive dechlorination of dichlorinated CEs into nonhalogenated volatiles. Overall, the results of the present study demonstrate the potential, feasibility, and environmental safety of this nanobioremediation approach.

Side Effects of Pesticides and Metabolites in Groundwater: Impact on Denitrification.

The impact of two pesticides (S-metolachlor and propiconazole) and their respective main metabolites (ESA-metolachlor and 1,2,4-triazole) on bacterial denitrification in groundwater was studied. For this, the denitrification activity and the bacterial diversity of a microbial community sampled from a nitrate-contaminated groundwater were monitored during 20 days in lab experiments in the presence or absence of pesticides or metabolites at 2 or 10 μg/L. The kinetics of nitrate reduction along with nitrite and N2O production all suggested that S-metolachlor had no or only little impact, whereas its metabolite ESA-metolachlor inhibited denitrification by 65% at 10 μg/L. Propiconazole and 1,2,4-triazole also inhibited denitrification at both concentrations, but to a lesser extent (29–38%) than ESA-metolachlor. When inhibition occurred, pesticides affected the reduction of nitrate into nitrite step. However, no significant differences were detected on the abundance of nitrate reductase narG and napA genes, suggesting an impact of pesticides/metabolites at the protein level rather than on denitrifying bacteria abundance. 16S rRNA gene Illumina sequencing indicated no major modification of bacterial diversity in the presence or absence of pesticides/metabolites, except for ESA-metolachlor and propiconazole at 10 μg/L that tended to increase or decrease Shannon and InvSimpson indices, respectively. General growth parameters suggested no impact of pesticides, except for propiconazole at 10 μg/L that partially inhibited acetate uptake and induced a decrease in microbial biomass. In conclusion, pesticides and metabolites can have side effects at environmental concentrations on microbial denitrification in groundwater and may thus affect ecosystem services based on microbial activities.

Toxicity of biogenic zinc oxide nanoparticles to soil organic matter cycling and their interaction with rice-straw derived biochar

Given the rapidly increasing use of metal oxide nanoparticles in agriculture as well as their inadvertent addition through sewage sludge application to soils, it is imperative to assess their possible toxic effects on soil functions that are vital for healthy crop production. In this regard, we designed a lab study to investigate the potential toxicity of one of the most produced nanoparticles, i.e. zinc oxide nanoparticles (nZnO), in a calcareous soil. Microcosms of 80 g of dry-equivalent fresh soils were incubated in mason jars for 64 days, after adding 100 or 1000 mg of biogenically produced nZnO kg−1 soil. Moreover, we also added rice-straw derived biochar at 1 or 5% (w: w basis) hypothesizing that the biochar would alleviate nZnO-induced toxicity given that it has been shown to adsorb and detoxify heavy metals in soils. We found that the nZnO decreased microbial biomass carbon by 27.0 to 33.5% in 100 mg nZnO kg−1 soil and by 39.0 to 43.3% in 1000 mg nZnO kg−1 soil treatments across biochar treatments in the short term i.e. 24 days after incubation. However, this decrease disappeared after 64 days of incubation and the microbial biomass in nZnO amended soils were similar to that in control soils. This shows that the toxicity of nZnO in the studied soil was ephemeral and transient which was overcome by the soil itself in a couple of months. This is also supported by the fact that the nZnO induced higher cumulative C mineralization (i.e. soil respiration) at both rates of addition. The treatment 100 mg nZnO kg−1 soil induced 166 to 207%, while 1000 mg nZnO kg−1 soil induced 136 to 171% higher cumulative C mineralization across biochar treatments by the end of the experiment. However, contrary to our hypothesis increasing the nZnO addition from 100 to 1000 mg nZnO kg−1 soil did not cause additional decrease in microbial biomass nor induced higher C mineralization. Moreover, the biochar did not alleviate even the ephemeral toxicity that was observed after 24d of incubation. Based on overall results, we conclude that the studied soil can function without impairment even at 1000 mg kg−1 concentration of nZnO in it.

Study on the preparation conditions and degradation performance of an efficient immobilized microbial agent for marine oil pollution

ABSTRACT In the process of handling marine oil spills accidents, the biological method has attracted wide attention due to its low cost and no secondary pollution. However, in the process of practical application, there are problems such as low microbial density and great influence of environmental factors when the oil is treated by spraying microorganisms on the sea surface. This study used immobilized microorganism technology to solve the above-mentioned problems. In this study, the bacteria immobilized on cinnamon shell (CS) with good degradation performance were obtained by optimizing preparation conditions. Under the optimal conditions of sodium alginate (SA) concentration of 4.57%, CS concentration of 1.28%, and the CaCl2 concentration of 2.45%, the degradation rate of diesel in 5 days reached 74.04%. The reusability of immobilized microbial agents was further studied. The study designed three cycles of repeated degradation experiments. The results showed that the degradation rate of diesel can still reach 60.12% after three times of reuse, which indicated the reusability of the immobilized microbial agents was excellent. The decrease in degradation rate of diesel was mainly related to the fragmentation of immobilized microbial agents and the decrease in microbial biomass.

SOIL MICROBIAL BIOMASS AND ENZYME ACTIVITIES RESPONSE TO COPPER AND MOLYBDENUM POLLUTION IN THE VICINITY OF ZANGEZUR COPPER AND MOLYBDENUM COMBINE, ARMENIA

The aim of this study was to define a relationship between heavy metal (Cu, Mo) pollution of soil and various extracellular enzyme activities. Six enzymatic activities involved in cycles of carbon, nitrogen, phosphorus and sulfur (β-glucosidase, chitinase, leucine-aminopeptidase, acid phosphomonoesterase, alkaline phosphomonoesterase, and arylsulphatase) as well as microbial biomass were determined in soil samples collected in the surroundings of Zangezur Copper and Molybdenum Combine. The investigations showed that pollution of soil with copper and molybdenum led to a decrease in microbial biomass and soil enzymatic activity, which in turn had a negative impact on cycles of chemical elements, in particular C, P, N and S. This gives reason to conclude that the changes in soil microbial biomass and enzymatic activity may act as indicators of soil biological activity and quality.

Nitrogen addition alters composition, diversity, and functioning of microbial communities in mangrove soils: An incubation experiment

Mangrove ecosystems are important for carbon storage due to their high productivity and low decomposition rates. Waterways have experienced increased nutrient loads as a result of anthropogenic activities and it is unclear how this may affect carbon and nutrient cycles in downstream mangroves that receive these nutrient-rich waters. Using a laboratory-based incubation experiment, this study aimed to assess the effects of nutrient addition on the diversity and structure of mangrove soil bacterial communities, as well as biomass and activity of the soil microbial community, under different oxygen conditions. Bacterial community diversity and composition was characterised using 16S rRNA gene sequencing and microbial activity was examined through the measurement of microbial respiration and the activities of enzymes associated with organic matter decomposition. Nitrogen addition caused clear shifts in bacterial community composition, with decreases in bacterial diversity and the abundance of sulfate-reducing bacteria. Microbial biomass also decreased with nitrogen addition under reduced oxygen incubations. Changes in bacterial community structure were accompanied by changes in the activity of some enzymes involved in carbon, nitrogen, and phosphorus cycling. Under reduced oxygen conditions, nitrogen addition resulted in a significant increase in the microbial metabolic quotient but no accompanying change in microbial respiration, which was explained by a decrease in microbial biomass. The findings of this study indicate that nitrogen loading has potential implications for microbial communities and carbon and nutrient cycling in mangrove environments that warrant further investigation under field conditions.

Assessment of the Influence of Pyrogenic Factors on the Biological Properties of Chernozems

Changes in the biological properties of chernozems caused by several pyrogenic agents have been studied in simulation experiments with the low-temperature plasma, infrared irradiation, straw burning, and fume of burning products. It has been shown that the pyrogenic effect has a complex nature, so that worsening of biological parameters depends on temperature, duration of fire episode, intensity of fume, ash impact, and soil moisture. Such integrated effect induced a decrease in microbial biomass by 39%, population of nitrogen-fixating bacteria by 29% versus the control values. The inhibition of dehydrogenase and catalase (oxidoreductase class) was 44–53%; the activity of hydrolase (phosphatase and invertase) was lower (by 16–18%). A maximal effect was recorded for the uppermost soil layer (0–1 сm) as compared to the lower 4–5 сm layer. Microbiological indices went down by 52–56% after placing the sample in the flame of a gas burner for 3 minutes, while soil enzyme activity decreased by 25–26%. For the latter, the duration of flame effect was of special importance; the correlation coefficient for dehydrogenase activity was –0.81; for invertase activity, –0.86; for catalase activity, –0.78; and for phosphatase activity, –0.85 (р < 0.01). Increasing IR irradiation also resulted in growing inhibition of biological indices. Even a minimal impact of fume of straw burning products (3 minutes at temperature 52°С) reliably decreased soil microbiological and biochemical parameters (by 4–19%, р < 0.05). Higher level of impact suppresses the biological activity by 20–30%.

Effects of Combined Ag and ZnO Nanoparticles on Microbial Communities from Crab Orchard Creek, Illinois, USA

The widespread use of Ag and ZnO nanoparticles (NPs) in commercial products has raised concern of their potential adverse impact on humans and the environment. These NPs most commonly enter the environment from the effluents of wastewater treatment plants (WWTPs). To understand the impact of these NPs on microbial communities, this study focused on adding environment-relevant concentrations of Ag (1 μg/L), ZnO (0.1 μg/L), and Ag+ZnO (1 μg/L+0.1 μg/L) to water collected from where the Carbondale Southeast WWTP effluent mixes with Crab Orchard Creek in IL, USA. Nanoparticles-spiked samples were withdrawn immediately and after 72 h for dynamic light scattering analysis. Optical density analysis by ultraviolet–visible spectroscopy, quantitative PCR analysis, and deoxyribonucleic acid sequencing were also conducted after 72 h. The results showed that ZnO NPs, at the studied concentration, were toxic, as a decrease in microbial biomass at Day 3 compared to the Control was reached, with an increase in mass fraction of nanoscale particles over time. However, when ZnO NPs were added in combination with Ag NPs, the adverse impact of ZnO NPs was mitigated, as an increase in microbial biomass was reached compared to the Control at Day 3, with a decrease in mass fraction of nanoscale particles over time. Ag NPs alone, at the studied concentration, did not bring significant impact on the microbial biomass. The relative abundance of the bacterial population affected the most by the addition of NPs was Firmicutes, with an increase in 13.74% compared to the Control when Ag+ZnO NPs were added. This study demonstrated the response of microbial communities to increased environment-relevant concentrations of NPs in a short period of time. The result will provide information that may aid in the preparation of guidance or regulations related to discharge of mixtures of NPs to surface water.