AimsPlant yield, nitrate accumulation risk, and the potential pathogenic microorganism are critical parameters in evaluating soil fertility management. The nitrate content in the soil-plant system is substantially driven by soil abiotic properties and soil and endophytic microorganisms which are also potential resources of plant pathogenicity. This study aimed to quantify the effects of citric acid (CA), alone or with dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP), on plant yield, nitrate accumulation risk and potential pathogenicity of soil-plant system.MethodsOur study contained six treatments: (1) control without CA or nitrification inhibitor (CK); (2) sole DCD application treatment (DCT); (3) sole DMPP application treatment (DMT); (4) sole CA application treatment (CAT); (5) CA + DCD application treatment (CADCT) and (6) CA + DMPP application treatment (CADMT). The nitrate contents, plant yields, and bacterial communities in soil and plant samples were analyzed.ResultsThe CA significantly reduced soil nitrate contents by 29.8%. Relative to sole CA application, extra nitrification inhibitor application significantly enhanced plant yields and decreased plant nitrate contents. The exclusive CA application could significantly stimulate the soil Actinobacteriota but reduce the soil pathogenicity, but extra nitrification inhibitors led to higher potential soil pathogenicity.ConclusionsThe single CA application could decrease nitrate accumulation risk and mitigating potential soil pathogenicity damage, while extra nitrification inhibitor application would intensify the performances of CA in decreasing plant nitrate accumulation but potentially enhancing the pathogenic. It deserves to emphasize the consideration of the tradeoffs among plant yield, nitrate accumulation risk, and potential pathogen risk when evaluating the effects of CA and nitrification inhibitors.

The oxidation of ammonia to nitrite, which constitutes the initial and rate-limiting step in the nitrification process, plays a pivotal role in the transformation of ammonia within soil ecosystems. Due to its susceptibility to a range of pollutants, such as heavy metals, pesticides, and pharmaceuticals, nitrification serves as a valuable indicator in the risk assessment of chemical contaminants in soil environments. Here, we analyzed the effects of cadmium (Cd) treatment on soil potential nitrification rate (PNR), and the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) communities. The results showed that, under 1 day incubation, the soil PNR with Cd 0.5 mg kg(-1) was a little higher but not statistically significant than that with zero mg kg(-1). Then, the soil PNR increased with the increasing Cd concentration from 0.5 to one mg kg(-1), and continuously declined from 1 to 10 mg kg(-1). Moreover, we predicted the bacterial functions of samples with hormetic Cd dose (one mg kg(-1)) by PICURSt (Phylogenetic Investigation of Communities Reconstruction of Unobserved States), and found that the expression of protein disulfide isomerase (PDI) increased with the hormetic Cd dose. PDI is known to enhance the activity of compounds containing -SH or -S-S which can help prevent oxidative damage to membranes. The soil PNR was significantly correlated with AOA abundance rather than AOB, even the abundance of AOB was higher than that of AOA, indicating that AOA functionally predominated over AOB. Our study effectively evaluated the Cd toxicity on soil microbial community and clearly illustrated the ecological niches of AOA and AOB in the agricultural soil system studied, which will be instructive for the sustainable development of agriculture.

Partial nitrification (PN) represents an energy-efficient bioprocess; however, it often confronts challenges such as unstable nitrite accumulation, nitrite oxidizing bacteria shocks, and slow reaction rate. This study established an acidophilic PN with self-sustained pH as low as 5.36. Over 120-day monitoring, nitrite accumulation rate (NAR) was stabilized at more than 97.9 %, and an ultra-high ammonia oxidation rate of 0.81 kg/m(3)& sdot;d was achieved. Notably, least NAR of 77.8 % persisted even under accidental nitrite oxidizing bacteria invasion, aeration delay, alkalinity fluctuations, and cooling shocks. During processing, despite detrimental effects on bacterial diversity, there was a discernible increase in acid-tolerant bacteria responsible for nitrification. Candidatus Nitrosoglobus, gradually dominated in nitrifying guild (2.15 %), with the substantially reduction or disappearance of typical nitrifying microorganisms. Acidobacteriota, a key player in nitrogen cycling of soil, significantly increased from 0.45 % to 9.98 %, and its associated nitrogen metabolism genes showed a substantial 215 % rise. AmoB emerged as the most critical functional gene influencing acidophilic PN, exhibiting significantly higher unit gene expression than other nitrification genes. Blockade tricarboxylic acid cycle, DNA damage, and presence of free nitrous acid exert substantial effects on nitrite-oxidizing bacteria (NOB), serving as internal driving forces for acidophilic PN. This highlights the reliable potential for shortening nitrogen transformation process.

Mining has led to dramatic ecosystem degradation, the destruction of vegetation and irreversible damage to soil structure and nutrient cycling; additionally, heavy metal (HM) contamination has affected soil nitrogen (N) cycle-associated microorganisms and disrupted soil aggregate structure. To explore the mechanism of soil N recovery in mining areas, we investigated the effects of two N fertilizers (urea (U) and ammonium chloride (AC)) and nine different fertilization patterns on the nitrification process and ammonia oxidizers in soil aggregates via incubation experiments. The results showed that different N treatments had different influences on the distribution of AOA and AOB amoA gene abundance and microbial community structure in soil aggregates. The AOB amoA gene abundance was significantly greater than the AOA amoA gene abundance in aggregates. The dominant species of AOA and AOB were Nitrososphaera and Nitrosospira , respectively, which were mainly found in microaggregates and accounted for 10.3 % to 25.0 % and 31.5 % to 60.1 %, respectively, of the microaggregates. Dissolved organic nitrogen (DON) can be used as an important variable to explain variations in AOA communities, and microbial nitrogen (MBN) content, tartaric acid content, cellulase activity and AOB amoA gene abundance can be used as important variables to explain variations in AOB communities. N fertilizer addition resulted in potential ammonia oxidation (PAO) values ranging from 0.079 to 0.236, 0.100 to 0.5953 and 0.146 to 0.905 mu g.NO2--N d(-1) g(-1) in mega-, macro- and microaggregates, respectively, which suggested that PAO values increased with decreasing aggregate size. In addition, the total nitrification potential (TNP) in macroaggregates was greater than that in mega- and microaggregates, which was the main reason for the increase in the NO3 content in macroaggregates. AOB amoA gene abundance was significantly positively correlated with TNP, and AOB amoA gene abundance was more significantly positively correlated with PAO values than was AOA gene abundance, which suggests that AOB dominated ammonia oxidation and nitrification processes in aggregates. Our research contributes to an understanding of the mechanisms underlying the effects of different types of N fertilizers on nitrification processes and ammonia oxidizers in soil aggregates and provides insights into N management in contaminated soils in mining areas.

The microbial induced partial saturation (MIPS) technique is the new environmentally friendly, cost-effective technique applicable under existing structures for mitigating sand liquefaction. The current study investigated the effectiveness of MIPS for mitigating sand liquefaction under undrained static loading. A series of undrained static triaxial tests were conducted to examine the influence of biogenic gas production through microbial denitrification on poorly graded sand at various relative densities. Initial batch experiments revealed that increased nitrate concentrations resulted in a decreased degree of saturation. Loosely and medium-dense saturated samples exhibited positive pore pressure during loading, which was reduced through biological desaturation, resulting in increased undrained shear strength ratios. Dense saturated and desaturated samples produced negative excess pore pressure, decreasing the undrained strength of treated samples due to dilative behavior. The undrained stress-strain behavior of loose and medium-dense sand transitioned from strain softening to strain hardening as the degree of saturation decreased from 100 to 90%. However, dense sand exhibited strain-hardening behavior with decreased saturation from 100 to 95%. Decreasing saturation levels reduced instability susceptibility, resulting in more stable soil behavior and decreasing the potential for large strains and instability. The study demonstrated a reduction in the Liquefaction Potential Index (LPI) for both loose and medium-dense sand as the degree of saturation decreased from 100 to 90%. These findings highlight the potential of MIPS as an effective technique for mitigating sand liquefaction and offer insights into its underlying mechanisms.

Replacing traditional plastics with biodegradable materials, such as poly(butylene adipate-co-terephthalate) (PBAT), is a reliable way to avoid farmland environmental pollution. However, the physical and mechanical properties of PBAT still have much to improve. Adding chain extenders to modify PBAT is one of the primary means. So far, the main chain extenders used are epoxy, anhydride, oxazoline, and isocyanate. In this paper, a blocked isocyanate chain extender with biological cyclodextrin as the skeleton material was designed and prepared(B3H35). When it was added to PBAT for melt blending at high temperature, the active isocyanate groups released by its deblocking reaction wound reacted with the terminal hydroxyl groups or carboxylic acid groups of PBAT to extend the molecular chain of PBAT, and then, a three-dimensional network was constructed based on dynamic hydrogen bonding, molecular entanglement, and physical cross-linking. As a result, the strength and toughness of PBAT improved simultaneously. Compared with pure PBAT, the tensile strength, elongation at break, and toughness of PBAT/B3H35 (2 wt %) increased by 17.7, 8.1, and 31.6%, respectively. In addition, 3,5-dimethylpyrazole, used as a blocking agent in this paper, is also released by deblocking during melt blending and endows PBAT/B3H35 with an excellent nitrification inhibition effect in agricultural soil. The experimental results show that the nitrification inhibition rate of the PBAT/B3H35 (3 wt %) reaches 80.64% after 35 days of landfill, significantly improving the utilization rate of the nitrogen fertilizer, thus reducing greenhouse gas emissions and environmental pollution. Overall, this work provides an idea and direction for designing and preparing functional chain extenders with simultaneous enhancement and toughening effects and nitrification inhibition functions for agricultural materials.

Fertilizer-intensive agriculture leads to emissions of reactive nitrogen (Nr), posing threats to climate via nitrous oxide (N2O) and to air quality and human health via nitric oxide (NO) and ammonia (NH3) that form ozone and particulate matter (PM) downwind. Adding nitrification inhibitors (NIs) to fertilizers can mitigate N2O and NO emissions but may stimulate NH3 emissions. Quantifying the net effects of these trade-offs requires spatially resolving changes in emissions and associated impacts. We introduce an assessment framework to quantify such trade-off effects. It deploys an agroecosystem model with enhanced capabilities to predict emissions of Nr with or without the use of NIs, and a social cost of greenhouse gas to monetize the impacts of N2O on climate. The framework also incorporates reduced-complexity air quality and health models to monetize associated impacts of NO and NH3 emissions on human health downwind via ozone and PM. Evaluation of our model against available field measurements showed that it captured the direction of emission changes but underestimated reductions in N2O and overestimated increases in NH3 emissions. The model estimated that, averaged over applicable U.S. agricultural soils, NIs could reduce N2O and NO emissions by an average of 11% and 16%, respectively, while stimulating NH3 emissions by 87%. Impacts are largest in regions with moderate soil temperatures and occur mostly within two to three months of N fertilizer and NI application. An alternative estimate of NI-induced emission changes was obtained by multiplying the baseline emissions from the agroecosystem model by the reported relative changes in Nr emissions suggested from a global meta-analysis: -44% for N2O, -24% for NO and +20% for NH3. Monetized assessments indicate that on an annual scale, NI-induced harms from increased NH3 emissions outweigh (8.5-33.8 times) the benefits of reducing NO and N2O emissions in all agricultural regions, according to model-based estimates. Even under meta-analysis-based estimates, NI-induced damages exceed benefits by a factor of 1.1-4. Our study highlights the importance of considering multiple pollutants when assessing NIs, and underscores the need to mitigate NH3 emissions. Further field studies are needed to evaluate the robustness of multi-pollutant assessments.

Permafrost-affected tundra soils are large carbon (C) and nitrogen (N) reservoirs. However, N is largely bound in soil organic matter (SOM), and ecosystems generally have low N availability. Therefore, microbial induced N-cycling processes and N losses were considered negligible. Recent studies show that microbial N processing rates, inorganic N availability, and lateral N losses from thawing permafrost increase when vegetation cover is disturbed, resulting in reduced N uptake or increased N input from thawing permafrost. In this review, we describe currently known N hotspots, particularly bare patches in permafrost peatland or permafrost soils affected by thermokarst, and their microbiogeochemical characteristics, and present evidence for previously unrecorded N hotspots in the tundra. We summarize the current understanding of microbial N cycling processes that promote the release of the potent greenhouse gas (GHG) nitrous oxide (N2O) and the translocation of inorganic N from terrestrial into aquatic ecosystems. We suggest that certain soil characteristics and microbial traits can be used as indicators of N availability and N losses. Identifying N hotspots in permafrost soils is key to assessing the potential for N release from permafrost-affected soils under global warming, as well as the impact of increased N availability on emissions of carbon-containing GHGs.

The aim of this work was to assess the biogeochemical role of riparian soils in the High Arctic to determine to what extent these soils may act as sources or sinks of carbon (C) and nitrogen (N). To do so, we compared two riparian areas that varied in riparian vegetation coverage and soil physical perturbation (i.e., thermo-erosion gully) in NE Greenland (74 degrees N) during late summer. Microbial soil respiration (0.4-3.2 mu mol CO2 m(-2) s(-1)) was similar to values previously found across vegetation types in the same area and increased with higher temperatures, soil column depth and soil organic C degradation. Riparian soils had low nitrate concentrations (0.02-0.64 mu g N-NO3- g(-1)), negligible net nitrification rates and negative net N mineralization rates (-0.58 to 0.33 mu g N g(-1) day(-1)), thus indicating efficient microbial N uptake due to low N availability. We did not find any effects of physical perturbation on soil respiration or on N processing, but the dissolved fraction of organic matter in the soil was one order of magnitude lower on the disturbed site. Overall, our results suggest that riparian soils are small N sources to high-Arctic streams and that a depleted dissolved organic C pool in disturbed soils may decrease exports to the adjacent streams under climate change projection.

Recent global warming models project a significant change in winter climate over the next few decades. The decrease in snowpack in the winter will decrease the heat insulation function of the snowpack, resulting in increased soil freeze-thaw cycles. Here, we examined the impact of winter freeze-thaw cycles on year-round dissolved nitrogen (N) and carbon (C) dynamics and their relationship with dissolved organic matter and microbial biomass in soil by conducting an in situ experimental reduction in snowpack. We investigated dissolved inorganic N (NH4+ and NO3-), dissolved organic N (DON), dissolved organic carbon (DOC), inorganic N leaching, soil microbial biomass, and microbial activities (mineralization and nitrification) in the surface soil of a northern hardwood forest located in Japan. Experimental snowpack reduction significantly increased the number of soil freeze-thaw cycles and soil frost depth. The NH4+ content of the surface soil was significantly increased by the amplified soil freeze-thaw cycles due to decreased snowpack, while the soil NO3- content was unchanged or decreased slightly. The gravimetric soil moisture, DON and DOC contents in soil and soil microbial biomass significantly increased by the snowpack removal in winter. Our results suggest that the amplified freeze-thaw cycles in soil increase the availability of DON and DOC for soil microbes due to an increase in soil freezing. The increases in both DON and DOC in winter contributed to the enhanced growth of soil microbes, resulting in the increased availability of NH4+ in winter from net mineralization following an increase in soil freeze-thaw cycles. Our study clearly indicated that snow reduction significantly increased the availability of dissolved nitrogen and carbon during winter, caused by increased soil water content due to freeze-thaw cycles in winter.