Soil Ammonium Research Articles

Phosphate recovery using activated sludge cyanophycin: Adsorption mechanism and utilization as nitrogen-phosphorus fertilizer

Recovery of biopolymers is an important way of resource recovery in wastewater treatment plants. However, their recycling and application pathways need to be further developed. This study explored the application potential of cyanophycin granule polypeptide (CGP) extracted from activated sludge in recycling phosphate from wastewater and used for nitrogen-phosphorus fertilizer. The results showed that the adsorption behavior of phosphate by CGP was well described by Elovich and Langmuir-Freundlich models, which reflects the uneven energy distribution on the surface of CGP and belongs to multimolecular layer adsorption. The maximal adsorption capacity of CGP to phosphate was 53.739 mg P/g, and the effects of anions and macromolecules on adsorption are negligible. The guanidyls in CGP were involved in binding phosphates, and the adsorption energies of CGP-HPO42– and CGP-H2PO4– calculated by DFT are –0.645 and –0.179 eV, respectively. Moreover, CGP absorbed phosphate significantly promoted the germination and growth of Brassica napus, and altered communities of rhizosphere rare species. Transcriptomic results of Brassica napus showed that nitrate uptake and arginine synthesis were down-regulated and arginine metabolism was up-regulated, which may be attributed to the degradation of CGP to arginine and ammonium in soil and uptake by plant. Nitrogen and phosphate released by CGP degradation promoted plant hormone signal transduction, thereby accelerating cell enlargement and plant growth. These results indicate that CGP can effectively recover phosphate and be utilized as a nitrogen-phosphorus fertilizer.

The effect of soil salt content and ionic composition on nitrification in a Fluvisol of the Yellow River Delta

Soil salinization is a common cause of land degradation and a major constraint on global food production. However, the effects that different salts have on soil biogeochemical processes such as nitrification are not fully understood. An incubation experiment was conducted with two different salt treatments applied at varying concentrations (sodium chloride addition, NaCl1: 2.06, NaCl2: 4.12, NaCl3: 5.00 g kg−1; sodium sulphate addition, NaS1: 5.00, NaS2: 6.07, NaS3:12.14 g kg−1). A Fluvisol soil was used as incubation medium and urea was supplied as the nitrogen source. Results showed that urease activities were reduced (28–76%) in salt treated soils on day 1, but recovered over time and finally surpassed that of the control on day 56. Moreover, the average urease activity of Na2SO4 treatments was 1.26 times higher than that of NaCl treatments on day 56. In addition, increasing soil salinity levels simultaneously reduced hydrolysis and nitrification rates, which led to the temporary accumulation of ammonium (NH4+-N) in soils for up to 14 days. The maximum contents of NH4+-N accumulation in NaCl3 and NaS3 were 1.64 and 1.48 times higher than those of NaCl1 and NaS1, respectively. Nitrification rates were inhibited more severely in soils dominated by Cl-. Low soil salt contents (less than 7.79 g kg−1) only delayed nitrification without reducing the total amount of nitrate (NO3--N) produced during the incubation. However, high salt contents (NaS3) significantly decreased the total NO3--N production. Our results indicate that nitrite oxidation process may also limit the speed of nitrification in salt-affected soils. Additionally, a new model is introduced to better simulate the dynamics of nitrification in salt-affected soils. In conclusion, soil salt content is the primary factor that inhibits nitrification. Anions affect the inhibitory strength of salinity on nitrification in soils with similar salinity levels, where Cl- is more suppressive than SO42-.

Unveiling the biogeochemical mechanism of nitrate in the vadose zone-groundwater system: Insights from integrated microbiology, isotope techniques, and hydrogeochemistry

Clarifying the biogeochemical mechanism of nitrate (NO3−) in the vadose zone-groundwater system, particularly in agricultural contexts, is crucial for mitigating groundwater NO3− pollution. However, comprehensive studies on the impacts of changes in chemical indicators and microbial communities on NO3− are still lacking. This paper aims to address this gap by employing hydrogeochemistry, stable isotopes, and microbial techniques to assess the NO3− biogeochemical processes in the vadose zone-groundwater system. The findings suggested that NO3− in upper soil layers was primarily influenced by plant root absorption, assimilation, and nitrification processes. The oxygen contents gradually decreased with the nitrification process, resulting in the occurrence of the denitrification. However, denitrification predominantly occurred in the 60–80 cm soil layer in the study area. The limited thickness of the denitrification layer results in less NO3− consumption, leading to increased NO3− leaching into groundwater. Hydrochemical and isotopic characteristics further indicated that groundwater NO3− concentrations were mainly controlled by nitrification, followed by denitrification and mixing processes. The 16S rRNA sequencing analysis revealed great influences of soil sampling depths and groundwater NO3− concentrations on the microbial community structure. Additionally, the PICRUSt2-based prediction results demonstrated a stronger potential for dissimilatory reduction of NO3− to ammonium (DNRA) in both soil and groundwater compared to the other processes, potentially due to the widespread presence of the nrfH functional genes. However, the chemical indicators and isotopes used in this study did not support the occurrence of DNRA process in the vadose zone-groundwater system. This finding highlights the importance of an integrated approach combining microbiological, isotopic, and hydrogeochemical data to comprehensive understanding biogeochemical processes. The study developed a conceptual model elucidating the NO3− biogeochemical processes in the vadose zone-groundwater system within an agricultural area, contributing to enhanced comprehension and advancement of sustainable management practices for groundwater nitrogen.

Enhancing remediation potential of heavy metal contaminated soils through synergistic application of microbial inoculants and legumes.

Soil microorganisms play a crucial role in remediating contaminated soils in modern ecosystems. However, the potential of combining microorganisms with legumes to enhance the remediation of heavy metal-contaminated soils remains unexplored. To investigate this, we isolated and purified a highly efficient cadmium and lead-tolerant strain. Through soil-cultivated pot experiments with two leguminous plants (Robinia pseudoacacia L. and Sophora xanthantha), we studied the effects of applying this microbial agent on plant nutrient uptake of soil nutrients, heavy metal accumulation, and the dynamics of heavy metal content. Additionally, we examined the response characteristics of inter-root microbial and bacterial communities. The results demonstrated that microorganisms screened from heavy metal-contaminated soil environments exhibited strong survival and adaptability in heavy metal solutions. The use of the Serratia marcescens WZ14 strain-phytoremediation significantly increased the soil's ammonium nitrogen (AN) and organic carbon (OC) contents compared to monoculture. In addition, the lead (Pb) and cadmium (Cd) contents of the soil significantly decreased after combined remediation than those of the soil before potting. However, the remediation effects on Pb- and Cd-contaminated soils differed between the two legumes following the Serratia marcescens WZ14 inoculation. The combined restoration altered the composition of the plant inter-rhizosphere bacterial community, with the increase in the relative abundance of both Proteobacteria and Firmicutes. Overall, the combined remediation using the tolerant strain WZ14 with legumes proved advantageous. It effectively reduced the heavy metal content of the soil, minimized the risk of heavy metal migration, and enhanced heavy metal uptake, accumulation, and translocation in the legumes of S. xanthantha and R. pseudoacacia. Additionally, it improved the adaptability and resistance of both legumes, leading to an overall improvement in the soil's environmental quality. These studies can offer primary data and technical support for remediating and treating Cd and Pb in soils, as well as rehabilitating mining sites.

Moderate water deficit and nitrogen application rate are conducive to improving the nitrogen uptake and yield of greenhouse tomatoes

Nowadays, improper irrigation and fertilization result in a waste of resources and a decrease in tomato production. In this study, we set three irrigation intervals (W1, W2 and W3 indicated upper and lower limit of irrigation of 65–75% θFC, 75–85% θFC and 85–95% θFC) and three nitrogen application rates (N1, N2 and N3 indicated nitrogen application rates of 120, 180 and 240 kg hm−2). The HYDRUS–2D model was first calibrated and validated using data collected during a two–year field investigation and then applied to explore the rules of soil water and nitrogen movement and root uptake. The Entropy weight TOPSIS model was optimized water and nitrogen management. Reliable estimates of soil nitrate nitrogen concentrations (R2 = 97%–99%, MRE = 0.05–0.19 and RMSE = 0.023–0.110), crop N uptake (R2 = 88%–99%, MRE = 0.17–0.44 and RMSE = 0.25–10.72), and soil water content (R2 = 82%–96%, MRE = 0.009–0.024 and RMSE = 0.003–0.007) were provided by HYDRUS–2D model. Based on the simulated results, the soil ammonium nitrogen was not easily affected by soil water movement and mainly distributed in 0–30 cm. W3 made soil water move deeper and carried nitrate nitrogen to accumulate in the deep soil comparison to W2 and W1. The combination of irrigation interval of 75–85% θFC and nitrogen application rate of 180 kg hm−2 improved root uptake, water use efficiency, nitrogen use efficiency and tomato yield. The evaluation result showed that N2W2 was the optimal water and nitrogen supply mode for our study. This study could promote the sustainable production of greenhouse tomatoes.

Moss patch size as a factor profoundly influencing soil nutrient characteristics and multifunctionality of temperate desert in Central Asia

Soil nutrients in desert ecosystems are influenced by various factors, and the presence of moss crust cover plays a significant role in determining the nutritional content of the surface soil. Moss crusts are distributed as patches within desert ecosystems, creating micro-ecosystems. However, the distribution pattern of soil nutrients under moss crust cover and the impact of patch size on soil nutrient content remain unclear. In this study, we assessed the patch size of mosses in field sites within the Gurbantünggüt Desert and investigated the content of total carbon (C), total nitrogen (N), total phosphorus (P), organic carbon (OC), ammonium (NH4+-N), nitrate (NO3–-N), and available phosphorus (AP) in both surface soil and sub surface soil. We employed linear and structural equation models to examine the regulatory effect of moss crust patch size on soil nutrient content. Our findings revealed that the C and N contents were significantly higher in the surface soil compared to the sub surface soil, while the AP content was significantly higher in the sub surface soil than in the surface soil. Additionally, a significant negative correlation was observed between the N content and patch area of the topsoil in 83% of the sample sites. Climate, soil properties, and moss patch size collectively influenced the multifunctionality of both surface soil and sub surface soil. Climatic factors exerted a greater impact on the surface soil, while soil properties and moss patch size had a stronger influence on the sub surface soil. These findings emphasize the variability in nutrient characteristics between the surface and sub surface soils of biocrusts, highlighting the influence of crust patch size on the nutrient characteristics and functions of desert soils. These insights have practical implications for land management and conservation strategies in arid regions, providing valuable knowledge for sustainable resource utilization and environmental preservation.

Mitigating the adverse effect of warming on rice canopy and rhizosphere microbial community by nitrogen application: An approach to counteract future climate change for rice

The adverse impact of climate change on crop production continues to increase, necessitating the development of suitable strategies to mitigate these effects and improve food security. Several studies have revealed how global warming negatively impacts the grain-filling stage of rice and that this effect could be mitigated by nitrogen; however, the impact of nitrogen application on rice canopy and rhizosphere microbial communities remains unclear. We conducted a study using an open-field warming system. Results showed that warming influenced rice canopy by decreasing aboveground biomass and harvest index, whereas nitrogen application had positive effect on rice production under warming conditions by increasing the plant nitrogen content, biomass, harvest index and soil fertilities. Moreover, soil ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) contents were significantly decreased under warming, which were higher after nitrogen application. Notably, warming and nitrogen fertilizer caused 19 % (P < 0.01) and 7 % (P < 0.05) variations, respectively, in the β diversity of the microbial community, respectively. The impact of warming was significant on NH4+-N-related microorganisms; however, this impact was weakened by nitrogen application for microbes in the rhizosphere. This study demonstrated that enhanced nitrogen fertilizer can alleviate the adverse impact of warming by weakening its effects on rhizosphere microbes, improving soil fertility, promoting rice nitrogen uptake, and increasing the aboveground biomass and harvest index. These findings provide an important theoretical basis for developing practical, responsive cultivation strategies.

Application of urea hydrogen peroxide: Degradation of glyphosate in soil and effect on ammonia nitrogen effectiveness and enzyme activity

Glyphosate is one of the most widely used pesticides globally. However, glyphosate and its residual metabolite, aminomethyl phosphonic acid (AMPA), are persistent and mobile chemicals. Large amounts of glyphosate residue can accumulate in the environment, causing adverse effects in organisms. Urea hydrogen peroxide (UHP) in soil slow-release H2O2 undergoes a Fenton-like reaction with Fe2+, and the resulting hydroxyl radical (·OH) degrades glyphosate. This experiment investigated the effects of three fertilisers (UHP, ferrous sulphate, and urea) on the degradation of glyphosate in agricultural soils and their effects on soil ammonia nitrogen effectiveness and enzyme activity. Among all treatments, the half-life of glyphosate in the mixed application of UHP and ferrous sulphate was the shortest (11.9 d), and its degradation rate was the highest (70.64%), degrading within 28 d. Throughout the experimental cycle, in 1–7 d, the application of UHP reduced the effect on indigenous microorganisms and maintained nitrogen availability and enzyme activity in the soil; in 7–14 d, the mixed application of UHP and ferrous sulphate alleviated the nitrification of soil nitrogen and reduced the loss of ammonia from the soil; in 14–28 d, the mixed or single application of UHP and ferrous sulphate and the low dose of glyphosate remaining in the soil had a catalytic effect on enzyme activity, promoting the secretion of catalase and nitratase, which participate in soil glyphosate degradation and nitrogen cycling. Therefore, this study provides a scientific basis for the in-situ remediation of herbicide-contaminated soil in agricultural fields using chemical fertilisers.

Symbiotic diazotrophs in response to yak grazing and Tibetan sheep grazing in Qinghai-Tibetan plateau grassland soils.

Grazing by local livestock is the traditional human practice in Qinghai-Tibetan Plateau grassland, and moderate intensity grazing can maintain high productivity and diversity of alpine grassland. Grazing ecosystems are often nitrogen-limited, but N2-fixing communities in response to yak grazing and Tibetan sheep grazing in Qinghai-Tibetan Plateau grassland have remained underexplored. In this study, we applied quantitative PCR quantitation and MiSeq sequencing of nifH under yak grazing and Tibetan grazing through a manipulated grazing experiment on an alpine grassland. The results showed that the grazing treatments significantly increased the soil ammonium nitrogen (AN) and total phosphorus (TP), but reduced the diazotrophs abundance. Compared with no grazing treatment, the composition of diazotrophs could be maximally maintained when the ratio of yak and Tibetan sheep were 1:2. The foraging strategies of grazing livestock reduced the legumes biomass, and thus reduced the diazotrophs abundance. Data analysis suggested that the direct key factors in regulating diazotrophs are AN and TP, and the changes of these two soil chemical properties were affected by the dung and urine of herbivore assemblages. Overall, these results indicated that the mixed grazing with a ratio of yak to Tibetan sheep as 1:2 can stabilize the soil diazotrophsic community, suggesting that MG12 are more reasonable grazing regimes in this region.

Comammox dominate soil nitrification under different N fertilization regimes in semi-arid areas of Northeast China

The newly identified complete ammonia oxidation (Comammox), which is capable of oxidizing ammonia directly to nitrate, has complemented the knowledge of nitrification in the global nitrogen (N) cycle. Knowledge of the community compositions and contributions to nitrification of autotrophic ammonia-oxidizing archaea (AOA) and bacteria (AOB) and Comammox remain void. In this study, the abundance, community compositions, and contributions to nitrification of AOA, AOB, and Comammox were observed in five N gradients (0, 90, 150, 210, and 270 kg ha−1) in a semi-arid area of Northeast China. The results indicated that, compared with low N application rates, higher N application rates significantly improved the soil ammonia monooxygenase (AMO) and the hydroxylamine oxidase (HAO) activities while total nitrogen (TN) was noted to be the main factor driving AMO and HAO activities. Soil potential nitrification rate (PNR) significantly increased with the increase in N application rate, and soil PNR was positively correlated with TN, nitrate nitrogen (NO3−-N), soil organic matter (SOM), and ammonium nitrogen (NH4+-N). The structural equation model (SEM) showed that TN was the main factor driving the community composition of Comammox; SOM had a greatest effect on the community composition of AOA while NH4+-N had a greatest effect on the community composition of AOB. The soil PNR had a direct effect on the yield. Overall, the findings of this study highlighted that N application was more conducive to the reproduction of soil nitrifying microorganisms while Comammox was the dominant contributor to nitrification under N fertilization regimes in the semi-arid area of Northeast China.

Tree-Structured Parzan Estimator–Machine Learning–Ordinary Kriging: An Integration Method for Soil Ammonia Spatial Prediction in the Typical Cropland of Chinese Yellow River Delta with Sentinel-2 Remote Sensing Image and Air Quality Data

Spatial prediction of soil ammonia (NH3) plays an important role in monitoring climate warming and soil ecological health. However, traditional machine learning (ML) models do not consider optimal parameter selection and spatial autocorrelation. Here, we present an integration method (tree-structured Parzen estimator–machine learning–ordinary kriging (TPE–ML–OK)) to predict spatial variability of soil NH3 from Sentinel-2 remote sensing image and air quality data. In TPE–ML–OK, we designed the TPE search algorithm, which encourages gradient boosting decision tree (GBDT), random forest (RF), and extreme gradient boosting (XGB) models to pay more attention to the optimal hyperparameters’ high-possibility range, and then the residual ordinary kriging model is used to further improve the prediction accuracy of soil NH3 flux. We found a weak linear correlation between soil NH3 flux and environmental variables using scatter matrix correlation analysis. The optimal hyperparameters from the TPE search algorithm existed in the densest iteration region, and the TPE–XGB–OK method exhibited the highest predicted accuracy (R2 = 85.97%) for soil NH3 flux in comparison with other models. The spatial mapping results based on TPE–ML–OK methods showed that the high fluxes of soil NH3 were concentrated in the central and northeast areas, which may be influenced by rivers or soil water. The analysis result of the SHapley additive explanation (SHAP) algorithm found that the variables with the highest contribution to soil NH3 were O3, SO2, PM10, CO, and NDWI. The above results demonstrate the powerful linear–nonlinear interpretation ability between soil NH3 and environmental variables using the integration method, which can reduce the impact on agricultural nitrogen deposition and regional air quality.

Responses of soil N-cycle enzyme activities to vegetation degradation in a wet meadow on the Qinghai-Tibet Plateau

Soil enzymes play a vital role in the functioning of wetland ecosystems, driving energy flow and material cycling processes. Gahai wet meadow, one of the important components of alpine wetlands on the Qinghai-Tibet Plateau, has suffered serious degradation in the last 30 years due to climate change and human activities. We studied the spatial and temporal heterogeneity of soil nitrogen content and nitrogen (N)-cycle enzyme activities (i.e., urease, protease, nitrate reductase and nitrite reductase) in four degraded wet meadows in the Gahai wetlands. Our results suggested that with increasing wet meadow degradation, there was a significant decrease in soil water content, total nitrogen, ammonium nitrogen, microbial biomass nitrogen content, protease activities, and nitrite reductase activities; Conversely, soil temperature, nitrate nitrogen content, urease activities, and nitrate reductase activities increased significantly. Soil urease, protease, and nitrite reductase activities significantly decreased with increasing soil depth;The highest activity levels of the three N-cycle enzymes were observed in July and August. The linear mixed modeling results indicated that there were significant effects of degradation level and soil depth and their interactions on soil nitrate reductase and nitrite reductase activities (p &amp;lt; 0.01), while soil depth had significant effects only on soil urease and protease activities (p &amp;lt; 0.01). Redundancy analyses showed that soil ammonium and nitrate nitrogen were the main drivers of changes in soil N-cycle enzyme activity during the degradation of wet meadows. In summary, our study sheds light on the processes of soil enzyme activity in an alpine wetland ecosystem and provides valuable information for understanding the N cycling in these complex systems.

Nitrous oxide and methane emissions from a Ferralsol as affected by loblolly pine cultivation time in subtropical Brazil

We hypothesized that the age of loblolly pine stands influences soil methane (CH4) and nitrous oxide (N2O) emissions. This is a relevant topic to be studied in subtropical Brazil, where the pine plantation area is increasing considerably. We evaluated N2O and CH4 emissions for two years in a Ferralsol under loblolly pine (Pinus taeda L.) stands of 1, 9 and 18 year-olds and a native forest (NF). We calculated the net CO2eq emission by considering the N2O and CH4 emissions from soil and the carbon (C) accumulation as litter in the forest floor. The soil N2O emission reduced gradually over the loblolly pine cultivation years, whereas CH4 uptake rates showed no clear pattern. Soil N2O emission showed a positive relationship with soil temperature in NF, and with soil ammonium and nitrate intensities in the pine stands. Soil CH4 uptake was inversely related to water-filled pore space in the pine stands, but this relationship was not observed in NF. The soil CH4 uptake rate was 4.6 times higher (p < 0.10) in NF than the average uptake in loblolly pine stands. On the other hand, soil N2O emissions in 9 and 18-year-old stands were similar (p > 0.10) to those in NF (1.3 kg N ha−1 yr−1). Our results suggest that cultivation with loblolly pine for 18 years can reduce soil N2O emission, and the uptake of CH4 in this system offsets 17 % of N2O emissions. Furthermore, the C accumulation as litter in the forest floor of the mature pine stands (9- and 18-year-old) generated a net emission of −1.6 Mg CO2eq ha−1 yr−1, showing to be an expressive offsetting mechanism. Therefore, we conclude that aged loblolly forests can reach N2O emissions levels comparable to those of NF, and the C sequestration in these forests floor can significantly contribute to offset N2O emissions and act as sink for net atmospheric CO2eq.

Different Response of Plant- and Microbial-Derived Carbon Decomposition Potential between Alpine Steppes and Meadows on the Tibetan Plateau

The alpine grasslands account for approximately 54.5% of the total carbon in China’s grasslands, and carbohydrate-active enzymes (CAZymes) play key roles in the turnover of carbon. However, the variation and factors influencing gene-encoding enzymes for plant- and microbial-derived carbon decomposition in alpine steppes and alpine meadows remain unclear. Here, the trends in microbial carbohydrate-active enzymes (CAZymes) and their responses to the decomposition of biomass of different origins were studied using metagenomics in the alpine steppes and alpine meadows on the Tibetan Plateau. Our results revealed the abundance of GTs and CBMs was higher in the alpine steppes than in the alpine meadows, whereas AAs were higher in the alpine steppes than in the alpine meadows. Soil properties (i.e., soil water content, soil ammonium nitrogen, and nitrate nitrogen) highly related to CAZyme genes (GTs, CBMs, and AAs) showed an abundant pattern between the alpine steppes and alpine meadows. Moreover, our results indicated that the relative abundance of genes encoding CAZymes involved in the decomposition of plant- (indicated by cellulose, hemicellulose, and lignin) and fungal-derived carbon (indicated by chitin and glucans) was higher by 8.7% and 10.1%, respectively, in the alpine steppes than in the alpine meadows, whereas bacterial-derived carbon (indicated by peptidoglycan) was lower by 7.9% in the alpine steppes than in the alpine meadows. Soil water content (SWC), nitrate nitrogen (NO3−), and pH influenced on the abundance of CAZyme genes involved in the decomposition of plant-, fungal-, bacterial-derived carbon. In addition, the dominant microbial phyla (Actinobacteria, Protebacteria, and Acidobacteria) mineralized carbon sources from plant- and microbial-derived carbon through their corresponding CAZyme families. In conclusion, our study compared plant- and microbial-derived carbon decomposition potentials and influencing factors to illustrate the contribution of dead biomass to carbon accumulation in alpine grasslands.

Aridity and soil fertility, not species richness, interact to affect temporal stability of primary productivity along a natural gradient in northern China

There is mounting evidence from experimental studies that drought and nutrient enrichment can interact to impact the biodiversity and productivity of terrestrial ecosystems. Whether such interactive effect influences plant diversity and the temporal stability of community productivity of natural ecosystems is unknown. To fill this knowledge gap, we combined a field survey of plant diversity and soil conditions with remote sensing temporal estimates of primary productivity in grasslands along a natural gradient in northern China. We found that aridity and soil ammonium (NH4+‐N) interacted to influence temporal stability of NDVI. That is, the relationship between ammonium and temporal stability of NDVI shifted from positive to negative due to increased standard deviation of NDVI with increasing aridity. Species richness was not related to temporal stability because it influenced the mean and standard deviation of NDVI proportionally. As a result, soil fertility outweighed the contribution of species richness to temporal stability. Our study demonstrates the synergistic effect of aridity and soil fertility, but not species richness, on temporal stability along a large natural gradient. Predicting how environmental drivers affect diversity and the stable provisioning of ecosystem services in real‐world ecosystems therefore requires a better understanding of the complex interactions among environmental drivers.

Effect of particle sizes of biochar on CO2 emissions in a poplar plantation of ancient Yellow River channel, China

Forest soil is a vital pool of organic carbon, which is sensitive to management. Biochar addition could change the CO2 emissions from soil, but its effects are still ambiguous. Moreover, the impacts of particle sizes of biochar on CO2 emissions are still unknown. In this study, a series of field experiments were conducted to investigate the effects of biochar addition on CO2 emissions in a poplar plantation (Populus nigra), China. Biochar with two application rates of (10 and 50 t/ha) and three particle sizes (3-1 mm, 1–0.1 mm, and <0.1 mm) was applied into the surface soil (0–10 cm), and the soil without biochar was set as control. The results showed that a high level of fine biochar addition (1–0.1 mm and <0.1 mm) had similar and positive effects on CO2 emissions by increasing the contents of soil ammonium, available phosphorus, easily oxidizable carbon, soil moisture, soil capillary pore, and the activity of β-glucosidase. However, biochar addition (1–0.1 mm and <0.1 mm) reduced the bioavailability of dissolved organic carbon (DOC), producing a negative relationship between DOC content and CO2 emissions. This investigation highlights the importance of biochar with different particle sizes in adjusting CO2 emissions from temperate soils.

Insight into the functional mechanisms of nitrogen-cycling inhibitors in decreasing yield-scaled ammonia volatilization and nitrous oxide emission: A global meta-analysis

Soil ammonia (NH3) volatilization and nitrous oxide (N2O) emission decrease nitrogen (N) utilization efficiency and cause some environmental problems. The N-cycling inhibitors are suggested to apply to enhance N utilization efficiency. Quantifying effects of N-cycling inhibitors on yield-scaled NH3 volatilization and N2O emission and functional genes could provide support for the optimal selection and application of N-cycling inhibitor. We conducted a meta-analysis to reveal the effects of N-cycling inhibitors on soil abiotic properties, functional genes and yield-scaled NH3 volatilization and N2O emission by extracting data from 166 published articles and linked their comprehensive relationships. The N-cycling inhibitors in this meta-analysis mainly includes nitrification inhibitors 3, 4-dimethyl pyrazole phosphate, dicyandiamide and 2-chloro-6-trichloromethylpyridine, urease inhibitor N-(n-butyl) thiophosphoric triamide and biological nitrification inhibitors methyl 4-hydroxybenzoate and 1, 9-decanediol. The N-cycling inhibitor applications significantly increased alkaline soil pH but significantly decreased acidic soil pH. The N-cycling inhibitors decreased soil AOB amoA gene abundances mostly under the condition of pH 4.5–6 (mean: 212%, 95% confidence intervals (CI): 249% and −176%) and significantly decreased nirS gene (mean: 39%; 95% CI: 72% and −6%). The yield-scaled NH3 volatilization was significantly decreased by the N-cycling inhibitors under the condition of soil pH = 7–8.5 (mean: 45%; 95% CI: 59% and −31%). The yield-scaled N2O emission was also significantly reduced by all N-cycling inhibitors and had negative correlations with the soil nirK and nirS gene abundances. The effects of N-cycling inhibitors on soil pH, ammonium-N, nitrate-N and nitrifying and denitrifying genes and yield-scaled NH3 volatilization and N2O emission were dominated by the inhibitor types, soil textures, crop species and environmental pH. Our study could provide technical support for the optimal selection and application of N-cycling inhibitor under different environmental conditions.

Harnessing nitrate over ammonium to sustain soil health during monocropping.

In achieving food security and sustainable agricultural development, improving and maintaining soil health is considered as a key driving factor. The improvement based on different forms of nitrogen fertilization has aroused great public interest in improving and restoring monocropping obstacles for specific soil problems. For this, a short-term cucumber cropping field experiment was conducted in the subtropical region of China under four fertilization treatments: ammonium (AN), nitrate (NN), ammonium with dicyandiamide (AN+DCD), nitrate with dicyandiamide (NN+DCD). In this study, we measured the effects of nitrogen forms addition on plant productivity and soil health in a monocropping system over seven seasons. To systematically evaluate soil health, a wide range of soil environmental factors were measured and incorporated into the soil health index (SHI) by entropy method. Compared with ammonium treatment (SHIAN = 0.059, SHIAN+DCD = 0.081), the positive effect of nitrate was mainly reflected in improving soil health (SHINN = 0.097, SHINN+DCD = 0.094), which was positively correlated with the increase in plant productivity of cucumber after seven seasons of monocropping. The most critical factor affecting SHI is soil ammonium nitrogen content, which was negatively correlated with plant productivity. Nitrate promotes soil health and plant productivity by optimizing soil environmental factors. The study thus emphasized the necessity of nitrate input for the sustenance of soil-crop ecosystems, with the consequent possibility of application of the results in planning monoculture obstacle prevention and management measures.

Litterfall quality modulates soil ammonium and nitrate supply through altering microbial function in bamboo encroachment of broadleaf forests

Plant invasion can change soil microbial function and nitrogen (N) supply through the input of litter with different qualities and quantities, among other factors. However, the underlying mechanism for litter quality to regulate soil N mineralization via microbial function with plant invasion remains unclear. We examined the effect of litterfall with contrasting chemical properties on soil net ammonification and nitrification rates, enzyme activity, and associated microbial function using reciprocal litterfall transplanting between a natural broadleaf forest and a Moso bamboo forest formed after the encroachment of a natural broadleaf forest. Our results showed that, on average, litterfall removal decreased ammonification rates by 33.6% but increased nitrification rates by 137.8%, while litterfall replacement increased nitrification rates by 55.9% in the natural broadleaf forest. Litterfall removal increased ammonification rates by 33.9%, while litterfall replacement increased ammonification rates by 42.1% at the end of the experiment in the bamboo forest. Structural equation modeling revealed that higher quality litterfall (higher cellulose content and lower lignin/N ratio) from the broadleaf forest enhanced net ammonification by altering fungal composition and increasing their ligninolytic capacity. However, the lower quality litterfall from the bamboo forest increased net nitrification rates through altering bacterial community and increasing urease activity. Our results indicate that the increased N supply resulting from litterfall replacement could counteract the low NH4+ availability in the bamboo forest soil, but not in the broadleaf forest soil. The contrasting modulation effects of litterfall quality on soil mineral N production would have cascading effects on bamboo encroachment and forest succession with implications for ecosystem management.

Arbuscular mycorrhizal hyphae selectively suppress soil ammonia oxidizers – but probably not by production of biological nitrification inhibitors

Arbuscular mycorrhizal hyphae selectively suppress soil ammonia oxidizers – but probably not by production of biological nitrification inhibitors