Nitrification Capacity Research Articles

Climate controls on nitrate dynamics and gross nitrogen cycling response to nitrogen deposition in global forest soils

Understanding the patterns and controls regulating nitrogen (N) transformation and its response to N enrichment is critical to re-evaluating soil N limitation or availability and its environmental consequences. Nevertheless, how climatic conditions affect nitrate dynamics and the response of gross N cycling rates to N enrichment in forest soils is still only rudimentarily known. Through collecting and analyzing 4426-single and 769-paired observations from 231 15N labeling studies, we found that nitrification capacity [the ratio of gross autotrophic nitrification (GAN) to gross N mineralization (GNM)] was significantly lower in tropical/subtropical (19%) than in temperate (68%) forest soils, mainly due to the higher GNM and lower GAN in tropical/subtropical regions resulting from low C/N ratio and high precipitation, respectively. However, nitrate retention capacity [the ratio of dissimilatory nitrate reduction to ammonium (DNRA) plus gross nitrate immobilization (INO3) to gross nitrification] was significantly higher in tropical/subtropical (86%) than in temperate (54%) forest soils, mainly due to the higher precipitation and GNM of tropical/subtropical regions, which stimulated DNRA and INO3. As a result, the ratio of GAN to ammonium immobilization (INH4) was significantly higher in temperate than in tropical/subtropical soils. Climatic rather than edaphic factors control heterotrophic nitrification rate (GHN) in forest soils. GHN significantly increased with increasing temperature in temperate regions and with decreasing precipitation in tropical/subtropical regions. In temperate forest soils, gross N transformation rates were insensitive to N enrichment. In tropical/subtropical forests, however, N enrichment significantly stimulated GNM, GAN and GAN to INH4 ratio, but inhibited INH4 and INO3 due to reduced microbial biomass and pH. We propose that temperate forest soils have higher nitrification capacity and lower nitrate retention capacity, implying a higher potential risk of N losses. However, tropical/subtropical forest systems shift from a conservative to a leaky N-cycling system in response to N enrichment.

Factors affecting the enrichment of heterotrophic nitrifying aerobic denitrifying bacteria in municipal wastewater treatment systems and analysis of differences in nitrogen metabolism

In this study, a four-stage MPSR process was employed for the treatment of urban wastewater. Three different conditions were established by controlling dissolved oxygen (DO) concentration, organic load rate (OLR), and influent pH value to examine pollutant removal effects and the changes of the heterotrophic nitrification-aerobic denitrification (HN-AD) functional bacteria communities. The factors driving changes in the HN-AD bacterial community and differences in nitrogen metabolism were revealed in the urban wastewater treatment system. The results showed that by forming anoxic/aerobic alternate oxygen environments and increasing influent OLR and pH, various HN-AD bacteria (Pseudomonas, Aeromonas, Flavobacterium) were enriched in the system, leading to improved removal capacity for NH4+-N and TN. Under optimal condition, the removal rates of NH4+-N and TN were 94.0 % and 78.7 % respectively. The dominant species of HN-AD bacteria were influenced by OLR and pH. The HN-AD bacteria exhibited the capacity for heterotrophic nitrification and aerobic denitrification within the system. This study provides a technological basis for the application of HN-AD bacteria for wastewater treatment.

Influence of Zeolite and Biohumus on the Nitrate Regime and Nitrification Capacity of Meadow-Gray Soils

Influence of Zeolite and Biohumus on the Nitrate Regime and Nitrification Capacity of Meadow-Gray Soils

Aridity creates global thresholds in soil nitrogen retention and availability.

Identifying tipping points in the relationship between aridity and gross nitrogen (N) cycling rates could show critical vulnerabilities of terrestrial ecosystems to climate change. Yet, the global pattern of gross N cycling response to aridity across terrestrial ecosystems remains unknown. Here, we collected 14,144 observations from 451 15 N-labeled studies and used segmented regression to identify the global threshold responses of soil gross N cycling rates and soil process-related variables to aridity index (AI), which decreases as aridity increases. We found on a global scale that increasing aridity reduced soil gross nitrate consumption but increased soil nitrification capacity, mainly due to reduced soil microbial biomass carbon (MBC) and N (MBN) and increased soil pH. Threshold response of gross N production and retention to aridity was observed across terrestrial ecosystems. In croplands, gross nitrification and extractable nitrate were inhibited with increasing aridity below the threshold AI ~0.8-0.9 due to inhibited ammonia-oxidizing archaea and bacteria, while the opposite was favored above this threshold. In grasslands, gross N mineralization and immobilization decreased with increasing aridity below the threshold AI ~0.5 due to decreased MBN, but the opposite was true above this threshold. In forests, increased aridity stimulated nitrate immobilization below the threshold AI ~1.0 due to increased soil C/N ratio, but inhibited ammonium immobilization above the threshold AI ~1.3 due to decreased soil total N and increased MBC/MBN ratio. Soil dissimilatory nitrate reduction to ammonium decreased with increasing aridity globally and in forests when the threshold AI ~1.4 was passed. Overall, we suggest that any projected increase in aridity in response to climate change is likely to reduce plant N availability in arid regions while enhancing it in humid regions, affecting the provision of ecosystem services and functions.

The hybrid MABR process achieves intensified nitrogen removal while N2O emissions remain low

The hybrid membrane aerated biofilm reactor (MABR) process represents a full-scale solution for sustainable municipal wastewater treatment. However, most of the existing hybrid MABR processes retain large aerobic bioreactor volumes for nitrification, which is undesirable for energy and carbon savings. In this study, we used the plant-wide modeling approach with dynamic simulations to examine a novel hybrid MABR configuration with aeration controls that change the anoxic and aerobic fractions of the bioreactor volume. Result showed that the novel hybrid MABR showed “swinging” nitrification and denitrification capacities in response to diurnal loadings, achieving intensified nitrogen removal performance under both warm and cold temperature scenarios. N2O emissions from the hybrid MABR were only 1/5 of the emissions from the conventional activated sludge. The model predicted higher CH4 emissions from the hybrid MABR than the activated sludge process due to the methanogen growth in the oxygen-depleted MABR biofilm layer. Future measurements for CH4 emission are needed to obtain a holistic picture of the carbon footprint of the hybrid MABR process.

Scots Pine (Pinus sylvestris L.) Ecotypes Response to Accumulation of Heavy Metals during Reforestation on Chalk Outcrops

As objects for reforestation, the least studied are carbonate substrates, which have a number of specific features in terms of mineral composition, the exchange of nutrients, and biological activity. The use of biological preparations of a consortium of bacteria of the genus Bacillus and mycorrhizal fungi of the genus Glomus in growing seedlings of Scots pine (Pinus sylvestris L.) on carbonate substrates provides the metabolic products; soluble and microelement salts function as catalysts for chemical reactions of exudates and soil products; and a greater amount of plant heavy metals (HM) Cu, Zn, Cd, and Pb accumulate in the soil. Among HMs, the random factors most strongly determined an accumulation of Cd (the influence rate of random factors h2x = 34.6%) and Pb (the influence rate of random factors h2x = 21.7%) in the plants. A trend of all studied HMs higher uptake by the Cretaceous pine (Pinus sylvestris var. cretacea (Kalen.) Kom.) in comparison with the P. sylvestris ecotype is revealed. Against the biological preparation background of Biogor KM and MycoCrop®, a greater value of the HM’s biological absorption in comparison with the option without biological preparations is noted. This process occurs against a background of a significant increase in the nitrification capacity in the chalk fine-grained substrate (soil aggregates < 1 mm in size), which is an indirect indicator of an increased intensity of microbiological processes. Spearman’s correlation was noted between the coefficient of accumulation of Cu, Zn, Cd, and Pb in the dry matter of Scots pine (P. sylvestris) seedlings and the nitrification capacity of substrate (rs = 0.610–0.744, p < 0.05), as well as the relationship between the nitrification capacity index of substrate and the coefficient of biological absorption of copper, zinc, and cadmium (rs = 0.543–0.765, p < 0.05). No relationship was found between the coefficient of biological absorption of lead and other soil chemical property indicators. HM absorption by plants was random. No correlations have been established between an accumulation of HMs and a content of total nitrogen, an absolute value of nitrate nitrogen, a humus content, or a pH. The significance of the work is the possibility of providing reliable reforestation with Scots pine (P. sylvestris) and Cretaceous pine (P. sylvestris var. cretacea) on the chalk outcrops using the biological preparations Biogor KM, MycoCrop®, and BGT* methodology and ensuring soil phytoremediation from HMs.

Organic and conventional farming systems shape soil bacterial community composition in tropical arable farming

Soils present a limited resource for agricultural production and bear a vast diversity of organisms crucial for crop health and the provision of ecosystem services. There is growing evidence that agricultural practices affect soil microbial community structure and function but currently, there is a knowledge gap when it comes to tropical arable farming systems. In this study, we investigated the long-term impact of organic and conventional production systems on bacterial communities in two field trial located on a rhodic and humic nitisol in the Central Highlands of Kenya. The field sites operate on a full factorial design, testing farming systems (organic vs conventional) and input levels (high vs low). Including four field replication we assessed soil bacterial community structure via amplicon sequencing of the 16S rRNA gene and soils capacity for nitrification and nitrous oxide reduction via qPCR of functional genes (bacterial and archaeal amoA, nosZ) after 12 years of distinct management and before the start of the 5th three-year crop rotation period in 2019. The abundances of amoA bearing nitrifiers and nosZ bearing nitrous oxide reducers were enhanced in the high input organic production system on humic but not in rhodic nitisols. For both soil types, high input organic production system resulted in distinct bacterial community structure with enhanced bacterial richness compared to conventional and low input production systems. In rhodic and humic nitisols 160 and 84 OTUs were found to be indicative for organic production system at high input levels organic. Taxa associated with this system were identified as potential primary decomposers or symbionts related to plant nitrogen fixation, suggesting organic fertilization strategies such as manure composting as major driver for changes in soil bacterial community structure. This study reveals that organic production systems at high input levels on tropical nitisols translates to distinct soil bacterial communities with increased capacity for soil processes that are crucial for crop nutrient supply.

Disentangling the effects of rice husk ash on increased plant growth and nitrogen recovery

Rice production generates large quantities of residues, whose disposal can pose environmental and health risks when not managed properly. The residue after rice husk combustion for energy production, rice husk ash (RHA), is currently underutilized despite its great potential as a soil conditioner. We aim to test the impact of RHA application on wheat growth, functional characteristics of the soil nitrifiers community and on N recovery using a 15N tracing greenhouse experiment. To distinguish between the effects caused by its liming capacity and P content, liming and P application treatments were included in the experiment. The amelioration of soil acidity (by both lime and RHA) lead to reduced losses of applied N fertilizer, but only RHA improved plant growth and plant N uptake. On the other hand, unlike RHA, lime application had strong effect on nitrification, increasing the potential maximal nitrification capacity (NEA) and reducing the affinity for N-NH4+ of soil nitrifiers (NHScom). The application of P reduced losses of applied 15N fertilizer particularly in the control pots, where additional P supply was likely critical to enhance N utilization by soil microorganisms. We therefore conclude that RHA effects on studied parameters are not only caused by soil pH amelioration nor by the P supply, but are likely driven by other inherent RHA properties (such as for instance its high content of macro- and micronutrients). The lack of observed effects on nitrification parameters and enhanced plant growth after RHA application can lead to considerably lower N losses and higher C sequestration in comparison to liming, while helping to solve the problems linked with RHA disposal.

Using Microorganismal Consortium and Bioactive Substances to Treat Seeds of Two Scots Pine Ecotypes as a Technique to Increase Re-Afforestation Efficiency on Chalk Outcrops

The present research is focused on various pine ecotypes’ seed reproduction in the chalky substrate, challenging environmental conditions on the carbonate soils on chalk outcrops in the south of the Central Russian Upland in relation to pine woods re-afforestation. The winter and spring sowing methods were studied, along with a pre-seeding treatment, by biopreparations based on a consortium of Glomales fungi, bacteria of the genus Bacillus, and bioactive substances. The seeds of two pine ecotypes, Pinus sylvestris L.; Pinus sylvestris var. cretacea Kalenicz exKom, underwent treatment. The study revealed that biopreparations and bioactive substances promote higher pine seed germination rates and ensure the stability and survivability of seedlings in an environment that is unfavorable for plant and tree ontogenesis. Applying biopreparations proved effective during spring sowing, whereas, in the case of winter sowing, their positive impact was not statistically significant. The net effect size of the three organized factors studied in the experiment (pine ecotype, biopreparation, sowing term) (h2x) on the “survivability of P. sylvestris seedlings” effective feature significantly increased from 90.8 to 93.8%. The effect size of the “pine ecotype” factor on seedling survivability in P. sylvestris was at its highest (14.4%) during the seedlings’ first-year growth period. The effect size of the “sowing term” factor was at its highest (79.4%) at the stage of seed germination. The effect size of the “biopreparation” factor was at its highest (44.0%) during the seedlings’ second-year growth stage. Our results indicate that it is preferable to create forest plantations on chalk outcrops using Pinus sylvestris var. cretacea ecotypes and with pre-sowing seed treatment via biopreparations based on a microorganismal consortium and Biogor KM. The Spearman correlation between the nitrification capacity of soil substrate and seedling survivability during the first three growth periods (from planting till the next year’s springtime) was of a moderate size (rs = 0.617–0.673, p < 0.05). To improve the growth and productivity of young and mature Scots pine stands, a Biogeosystem Technique (BGT*) methodology was developed.

Effects of biocarrier type and size on the performance of nitrification and simultaneous nitrification and denitrification

Four soft polyurethane biocarriers with different sizes and a hard polypropylene biocarrier were selected to evaluate the effects of material type and size on the nitrification and simultaneous nitrification and denitrification (SND) performance of the aerobic moving bed biofilm reactors (MBBR) in treating synthetic coking wastewater under different organic loading rates (OLR, 0.95, 0.65, 0.49 kg COD m−3 day−1). The attached biomass concentrations of the polyurethane biocarriers were 1.65 ± 0.15 g L−1, almost twice that of the polypropylene one (0.76 ± 0.05 g L−1), while the differences in the suspended biomass concentrations were relatively small (1.48 ± 0.18 g L−1 and 1.28 ± 0.06 g L−1, respectively). The SND efficiency of 32.43% ± 5.15% for all five MBBRs was achieved at an OLR of 0.95 kg COD m−3 d−1, which decreased to 8.48% ± 5.25% and 4.35% ± 2.99%, respectively, at lower OLRs. It was clear that OLR was an important factor affecting the SND performance. The MBBR using the smallest polyurethane biocarrier (10 mm × 10 mm × 10 mm) achieved complete nitrification at an OLR of 0.65 kg COD m−3 day−1, while the other ones achieved it at a lower OLR (0.49 kg COD m−3 day−1). The smallest polyurethane biocarrier exhibited a higher specific ammonium oxidizing rate (SAOR, 0.071 ± 0.007 g NH4+-N g−1 VSS day−1) than the other ones (0.045–0.050 g NH4+-N g−1 VSS day−1 for the larger size polyurethane ones and 0.023 ± 0.002 g NH4+-N g−1 VSS day−1 for the polypropylene one). Miseq analysis revealed that Nitrosomonas and Nitrospira were respectively the dominant AOB and NOB in all MBBRs. The polyurethane biocarriers enriched AOB and NOB in the biofilms as much as 14.6 and 9.7 times, while the polyethylene one only enriched them 3.8 and 2.2 times. Thus, the polyurethane biocarrier with smaller size was advantageous for improving nitrification capacity.

Exploration of the nitrogen contamination from sewers exfiltration to the unsaturated zone by modeling

Numerous elements, such as the degree of sewer degeneration, hydraulics, and geological conditions, influence the extent to which sewage pollutes the unsaturated zones of urban. The present study discussed the influence of sewer exfiltration on the urban unsaturated zone, using nitrogen from domestic sewage as a representative contaminant in combination with experiments, literature studies, modeling and sensitivity analysis. The study shows that soils with high sand content exhibit high permeability and strong nitrification capacity, and groundwater is more susceptible to contamination with nitrate. In contrast, the nitrogen in the clay texture or wet soils has short migration distances and a weak nitrification capacity. However, under such conditions, the accumulation of nitrogen can last for more than 10 years, and there is a possible threat of groundwater contamination due to the detection difficulty. The presence of sewer exfiltration and the damage degree of a sewer can be determined by the ammonium concentration at 1–2 m near the pipe or nitrate above the water table. The sensitivity analysis revealed that all parameters impact the nitrogen concentration in the unsaturated zone to varying degrees, four of which are the primary parameters: defect area, exfiltration flux, saturated water content and first-order response constant. In addition, changes in environmental conditions significantly influence the boundaries of the pollution plume, especially the horizontal. The research data collected in this paper will not only allow for a rigorous assessment of the study scenarios but will also provide data support for other researchers.

Pathways and Drivers of Gross N Transformation in Different Soil Types under Long-Term Chemical Fertilizer Treatments

Microbial-mediated nitrogen (N) dynamics is not only a key process for crop productivity, but also a driver for N losses. Therefore, a better understanding of N dynamics and controlling factors in different soil types is needed to better manage N fertilization in crop fields. To achieve this, a 15N tracing approach was used to quantify simultaneously occurring N transformation rates in four agricultural trials (>20 years chemical fertilizer application) with contrasting climatic and edaphic types (three upland soils and one paddy soil). The results showed that recalcitrant soil organic carbon (SOC) mineralization was the main source of NH4+ at all the sites, with rates ranging from 0.037 in fluvo-aquic soil to 3.096 mg kg−1 day−1 in paddy red soil. Autotrophic nitrification (ONH4) was the predominant NO3− production mechanism in the black and fluvo-aquic soils, whereas it was negligible in the upland and paddy red soils. Nitrification capacity, as an indicator of nitrate leaching risk, was in the order: upland red soil (1%) < paddy red soil (8%) < black soil (235%) < fluvo-aquic soil (485%), implying a high nitrate leaching risk in the last two soils. However, high microbial immobilization (41%) and abiotic adsorption (6%) decreased NO3− leaching in black soil. The partial least squares path modeling (PLS-PM) showed that SOC, temperature and pH were the main factors controlling nitrate immobilization, N mineralization and nitrification. In summary, even under similar chemical fertilization conditions, N transformation dynamics are expected to differ with respect to soil type. Therefore, N management strategies should be adjusted to soil type to control N losses and increase crop yield.

Fungus Pichia kudriavzevii XTY1 and heterotrophic nitrifying bacterium Enterobacter asburiae GS2 cannot efficiently transform organic nitrogen via hydroxylamine and nitrite.

Heterotrophic nitrification is a process of organic nitrogen degradation completed by the participation of heterotrophic nitrifying microorganisms, which can accelerate the nitrogen transformation process. However, the current research mainly focuses on heterotrophic nitrifying bacteria and their ammonium degradation capacities. And there is little accumulation of research on fungi, the main force of heterotrophic nitrification, and their capacities to transform organic nitrogen. In this study, novel heterotrophic nitrifying fungus (XTY1) and bacterium (GS2) were screened and isolated from upland soil, and the strains were identified and registered through GenBank comparison. After 24 h single nitrogen source tests and 15N labeling tests, we compared and preliminarily determined the heterotrophic nitrification capacities and pathways of the two strains. The results showed that XTY1 and GS2 had different transformation capacities to different nitrogen substrates and could efficiently transform organic nitrogen. However, the transformation capacity of XTY1 to ammonium was much lower than that of GS2. The two strains did not pass through NH2OH and NO2 - during the heterotrophic nitrification of organic nitrogen, and mainly generated intracellular nitrogen and low N2O. Other novel organic nitrogen metabolism pathways may be existed, but they remain to be further validated.

Revealing the behavior of perfluorooctane sulfonic acid in an aerobic granular sludge system: Fate and impact

The biogeochemistry (i.e., migration and transformation) and impacts of perfluorooctane sulfonic acid (PFOS) in an aerobic granular sludge (AGS) system have been studied. The results suggested that PFOS removal rates under 0.1, 0.5 and 5.0 mg/L PFOS treatment were 89.23 ± 0.92 %, 71.92 ± 1.45 % and 48.15 ± 1.90 %, respectively, which was mainly attributed to the adsorption mechanism involving electrostatic, hydrophobic and ionic bridging interactions. Meanwhile, the adsorbed PFOS deteriorated sludge flocculation. Compared with the control, 0.1 mg/L PFOS treatment increased the concentration of effluent suspended solids (ESS) from 70 ± 5 to 238 ± 15 mg/L. Interestingly, the denitrification performance of the AGS improved (i.e., total nitrogen (TN) average removal rate increased from 87.05 ± 0.21 % to 96.56 ± 0.05 %), which was contrary to the outcomes for activated sludge. Further analysis showed that PFOS reduced the percentage of norank_f_norank_o_Ardenticatenales, norank_f_Sphingomonadaceae and Candidatus_Competibacter maintaining the particle stability, which led to the decrease in AGS flocculation. In addition, the relative abundance of nitrite-oxidizing bacteria Nitrospira decreased under PFOS exposure, while the total abundance of denitrifying bacteria (mainly Dechloromonas) increased. This might enhance the short-cut nitrification and denitrification capacity of the AGS system and promote the removal of TN. However, PFOS had no obvious impact on the settleability of AGS and the transformation of chemical oxygen demand (COD) and soluble phosphorus (SOP). Our findings will provide theoretical insights and practical support for risk control in the process of treating fluoride-containing wastewater.

Food-based sizing criteria of bead filters with floating media in serial treatment with moving bed bioreactors

The bead filter and moving bed biological reactor (MBBR) are two common technologies used in tandem to remove solids and ammonia from recirculating aquaculture systems. While the sizing of these two technologies is well understood when designed separately, the same sizing guidelines lead to inefficiencies when the two are used together. This is primarily due to the sizing by part design philosophy not considering processes that occur in multiple system components. In response, the authors have reviewed and amended sizing recommendation to avoid unnecessary oversizing. This analysis presents three cases to examine how sizing by parts can lead to system inefficiencies and to lay out a better design approach. Case 1 utilizes the bead filter as a solids capture device, ignoring the impact of the system’s recirculating flow rate and bead filter’s nitrification capacity. Case 2 uses the bead filter’s volume to determine the system’s recirculating flow rate without considering the bead filter’s nitrification capacity. In Case 3 the bead filter’s nitrification capacity is utilized in sizing the moving bed reactor placed in series after the bead filter. In summary, the high-rate floating bead filters (Ω=2888 m3 day −1 m−3 media) should be utilized to remove solids prior to a moving bed reactor and the nitrification capacity of the floating bead filter should be consideration in the MBBR sizing. This will produce a more cost-effective design and result in a balanced design free of transport limitations.

MABR process development downstream of a carbon redirection unit: opportunities and challenges in nitrogen removal processes

ABSTRACT Carbon redirection has become the desired option for sustainable and energy-efficient wastewater treatment due to its contribution to a circular economy. However, its impact on downstream processes such as nitrification and denitrification requires further investigation. This research characterizes the nitrogen removal performance, footprint, aeration mode, and microbial composition of a flow-through membrane aerated biofilm reactor (MABR) downstream of a chemically enhanced primary treatment (CEPT) carbon redirection unit. The batch and long-term studies demonstrated relatively higher nitrification rates than those reported using conventional primary treated wastewaters. The results indicated that reducing carbon in the liquid train positively impacted nitrification by achieving 87 ± 12% (1.4 ± 0.4 g/m2.d) ammonia removal with an effluent 2.5 ± 2.8 mg/L ammonia concentration at a short hydraulic retention time (HRT) of 2.5 h. Despite the lower (1.9 ± 1) soluble COD:N, up to 75 ± 25% (0.6 ± 0.4 g/m2.d) total nitrogen removal was achieved at 4 h HRT by implementing intermittent aeration. The batch tests using the developed biofilms showed nitrification (denitrification) capacity up to 11 ± 1.7 gNH4-N/m2.d (8.5 ± 0.5 gNO3-N/m2.d) and 2.7 ± 0.6 gNH4-N/m2.d (2 ± 0.3 gNO3-N/m2.d) corresponding to ammonia and nitrate concentrations ranging from 10–30 mg/L and 2–10 mg/L, respectively. Microbial analysis indicated that the nitrifiers such as Nitrosomonas and Nitrospira were the dominant species. The ammonia-oxidizing, nitrite-oxidizing, and denitrifying bacteria relative abundances were 10.3 ± 1.5%, 20.7 ± 1.7%, and 20.0 ± 2.8% under continuous aeration and 1.3 ± 0.07%, 1.8 ± 0.09%, and 40.5 ± 3.1% under intermittent aeration, supporting the observed ammonia and total nitrogen removal processes, respectively. Overall, the results demonstrated that MABR downstream of the CEPT behave differently; thus, design guides should be updated accordingly.

Influence of long-term intensive use of irrigated meadow-chernozem soil on the biological activity and productivity of the arable layer

The research was carried out on the territory of the Russian Federation in the forest-steppe region of the south Western Siberia (Omsk state), in the long-term (43 years) stationary experiment. Sprinkling was used for irrigation in the experiment. The number of different physiological groups of microorganisms, the cellulolytic activity of the soil, and nitrification capacity were determined under the sowing of an eight-field grain-grass crop rotation (perennial grasses (Bunias orientalis L. + Bromopsis inermis L. + Galega orientalis Lam. 6–8 years old), spring barley Hordeum vulgare Leyss.—variety Sasha). Immobilization processes predominated in the soil under the sowed crops, it contributes to the preservation of soil organic matter (mineralization coefficient SAA/MPA < 1). The highest transformation ratio of soil organic matter, i.e. increased conversion of plant residues into organic matter, was noted with applying nitrogen-phosphorus fertilizers (N60P60) under the barley. The combination of irrigation factors and the use of mineral fertilizers (N30-60P60) were contributed to the growth of the microorganisms’ population, the amplification of decomposition of cellulose, and improvement of nitrification capacity in the soil. The perennial irrigation of the meadow-chernozem soil and the application of intensive technology of cultivation of crops in crop rotation stimulated the growth of the microorganisms’ population and didn’t detriment the ecological state of the soil.

Characteristics and influencing factors of soil nitrification potential in coastal salinized farmland

Understanding the nitrification capacity of coastal saline farmland soils and its main drivers is of great significance to regulate soil nitrification and improve the utilization efficiency of nitrogen fertilization in farmland. Using a combination of field investigations and laboratory analyses, we examined farmland soil nitrification potential and soil physical, chemical, and biological properties in the coastal muddy tidal flat saline soil area (Dongying and Dongtai). We established the correlation between soil properties and soil nitrification potential with multiple stepwise regression analyses and structural equation modeling (SEM). The results showed that soil pH value was relatively stable and other soil properties and soil nitrification potential varied in coastal saline farmland. The soil nitrification potential ranged from 0.04 to 10.42 mg·kg-1·d-1 and decreased with the increases of soil salinization level. Soil nitrification potential had the strongest correlation with soil organic matter, cation exchange capacity, and Cl-, with the correlation coefficient being 0.409, 0.397 and -0.337, respectively. The results of multiple stepwise regression analysis showed that Na+, silt, cation exchange capacity, and CO32-+HCO3- were the main influencing factors of soil nitrification potential. The results from the SEM analysis suggested that Na+, silt, cation exchange capacity, and CO32-+HCO3- directly affected soil nitrification potential, and soil organic matter, clay, Cl- and SO42- had indirect effects. In all, soil Na+ and cation exchange capacity were the two main factors affecting nitrification. Adjusting soil NaCl content and cation exchange capacity was an effective means of regulating soil nitrification.

Soil Nitrification Capacity as an Integral Indicator of Soil Fertility Monitoring

Soil Nitrification Capacity as an Integral Indicator of Soil Fertility Monitoring

Effects of iron-based substrate on coupling of nitrification, aerobic denitrification and Fe(II) autotrophic denitrification in tidal flow constructed wetlands

The aerobic properties of nitrification and the anaerobic properties of denitrification in constructed wetlands are difficult to reconcile. In this study, two constructed wetlands were constructed with pyrite and steel slag in combination with zeolite, and their respective nitrification and denitrification capacities were evaluated under different tidal strategies. The steel slag wetland achieved 70.89 % and 46.04 % removal rates of NH4+-N and total nitrogen (TN), and the carbon consumption of denitrification was 1.51 mg BOD/mgN, which was better than pyrite wetland. Microbial analysis showed that Fe(II) autotrophic denitrification and aerobic denitrification occurred in both wetlands, and they were coupled with nitrification to achieve simultaneous removal of NH4+-N and TN. Microbial co-occurrence network and k-core decomposition analysis indicated that the core genus of steel slag wetlands was nitrifying bacteria. This study provides new insights into the application of tidal flow wetlands to treat rural sewage.