Soil Ammonium Research Articles

In silico evaluation of plant nitrification suppression effects on agroecosystem nitrogen loss

AbstractNitrification regulates the potential for nitrogen (N) loss from ecosystems because it converts ammonium to nitrate, which is susceptible to leaching and gaseous emissions. Crops can suppress the microbes that perform nitrification by exuding nitrification‐inhibiting compounds from their roots and taking up available ammonium. However, the effect of nitrification suppression on agroecosystem N losses remains poorly characterized, and a lack of temporal synchrony between nitrification, N losses, and nitrification suppression by plants could limit the effect of nitrification suppression. We used the DayCent‐CABBI model to evaluate the effectiveness of the suppression of nitrification by sorghum to reduce N2O emissions and nitrate leaching in an energy sorghum/soybean rotation at the Energy Farm in Urbana‐Champaign, IL. We simulated nitrification suppression at the measured levels (MeasNS) and at the maximum measured level applied to the entire growing season (MaxNS), and we also explored ways to better utilize nitrification suppression by altering the timing of urea–ammonium–nitrate fertilizer applications. Model experiments showed that most nitrification occurred immediately after fertilizer was applied, whereas nitrification suppression began to ramp up more than a month after planting. On an annual basis, MeasNS experiments showed a 1%–2% reduction in annual N2O emissions relative to no nitrification suppression (NoNS), and MaxNS experiments showed a 4%–9% reduction in annual N2O emissions relative to NoNS. Both nitrification suppression levels showed <1% reduction in nitrate leaching. Altering the timing of fertilizer applications to better synchronize nitrification suppression with high soil ammonium levels had mixed effects on annual N2O emissions and nitrate leaching and sometimes resulted in increased N losses. The timing of simulated N2O emissions shifted with the timing of fertilization, and N2O emissions from denitrification increased when N2O emissions from nitrification decreased. Increasing N retention during the non‐growing season may be more effective than growing‐season nitrification suppression for reducing annual N losses in the rainfed Midwest.

Factors affecting N2O fluxes from heavy metal-contaminated mangrove soils in a subtropical estuary

A 1-year field monitoring program was carried out to observe seasonal variation in N2O fluxes at two typical mangrove wetlands in a subtropical estuary. The soils in the island-type mangrove wetland had a higher level of heavy metal(loid) contamination and a lower level of salinity compared to the small bay-type mangrove wetland. While there was a high level of similarity in the seasonal variation pattern of N2O fluxes between the two investigated sites with both being significantly higher in summer than in other seasons, the average of N2O fluxes in the island-type mangrove wetland was 7.19 μg·m−2·h−1， which tended to be lower compared to the small bay-type mangrove wetland (15.63 μg·m−2·h−1). Overall, N2O flux was closely related to soil-borne heavy metal(loid)s, showing a trend to decrease with increasing concentration of these heavy metal(loid)s. The N2O fluxes increased with decreasing abundance of either denitrifiers or nitrifiers. But the opposite was observed for the anammox bacteria present in the soils. The anammox bacteria were more sensitive to heavy metal(loid) stress but more tolerated high salinity encountered in the investigated soils compared to the denitrifiers or nitrifiers. It appears that anammox reactions mediated by anammox bacteria played a key role in affecting the spatial variation in N2O fluxes from the mangrove soils in the study area. And an increased level of ammonium in soils tended to promote the activity of anammox bacteria and consequently enhanced N2O emission from the mangrove soils.

Determination of Paddy Soil Ammonia Nitrogen Using Rapid Detection Kit Coupled with Microplate Reader.

Indophenol blue colorimetry has been widely used for determining soil ammonia nitrogen, but this method has some disadvantages, such as complex reagent preparation, high toxicity, and long colorimetric time. Hence, we aimed to develop a rapid soil ammonia nitrogen determination method using a rapid detection kit. In order to select a suitable extractant, different concentrations of KCl and NaCl solutions were used to extract soil. The ammonia nitrogen content in different types of soils was determined using a rapid detection kit (purchased from Zhejiang Luheng Environmental Technology Limited Company) coupled with a microplate reader. The kit method was compared with the traditional indophenol blue colorimetry method. The results showed no significant difference between the 1 mol·L-1 KCl extraction kit method and indophenol blue colorimetry (p > 0.05). The linearity of the working curve was smooth, the linear detection range was 0.0-2.00 mg·L-1, the average relative standard deviation was 7.00% (n = 5), the standard addition recovery rate was 89.31-118.23%, and the detection limit were was 0.074 mg·L-1. We concluded that the 1 mol·L-1 KCl extraction kit method can be applied to determine the ammonia nitrogen content of paddy soil with different chemical properties. The 1 mol·L-1 KCl extraction kit method has the advantage over indophenol blue colorimetry due to its simple reagent preparation, convenient operation, and shorter detection time (the coloring and colorimetric time for 96 samples was only 30 min using the kit method coupled with a microplate reader). Hence, it has the potential for application due to its rapid determination of soil samples in large quantities.

Effects of Long-Term Chemical and Organic Fertilizer Application on Soil Phosphorus Fractions in Lei Bamboo Plantations

Phosphorus (P) is a key nutrient in forest ecosystems in subtropical regions. However, the effects of the long-term application of organic amendments on P availability are poorly understood. Here, we compared the soil P fractions and associated soil properties in southern Chinese Lei bamboo plantations using both an intensive management system (IMS) and a traditional management system (TMS). The results show that the IMS significantly (p < 0.05) increased the soil total organic carbon (C), soil ammonium N (NH4-N), total P, and available potassium content; microbial biomass C and P content; P activation coefficient, and soil C:P ratios, while significantly (p < 0.05) decreasing pH and microbial C:P. The labile-P-to-total-phosphorus-content ratio increased significantly in the IMS (46%) compared with that in the TMS (32%). The selected soil properties (except nitrate [NO3−N]) were significantly related to soil P fractions (except for concentrated HCl-extracted organic P). The IMS had a higher C:P ratio and labile P content than the TMS, suggesting that the IMS could promote soil P transformation and availability. Overall, the IMS increased soil P availability and supply capacity, and the changes in P forms could be a risk factor for P loss.

Changes in soil fungal community composition and functional groups during the succession of Alpine grassland

Background and aimsThis study explores trends in soil fungal patterns, potential functions and their responses to carbon and nitrogen applications over alpine grassland succession in the Qilian Mountain area of China.MethodsThe soil fungal community was characterized via Illumina sequencing of ITS genes. The FUNGuild database was used to predict functional groups in alpine grassland succession from swamp meadow to alpine meadow and steppe meadow. The levels of soil carbon and nitrogen, vegetation carbon and nitrogen, and soil enzyme activity were also assessed.ResultsSoil fungal operational taxonomic units increased from swamp meadow to alpine meadow stage and then reached a relatively stable state in steppe meadow successional stage. This result is consistent with the changing trend of sobs and Chao1 index. Moreover, the soil fungal community differed significantly between different succession stages. During succession, while most phyla of soil fungi followed linear decreasing trends, Ascomycota was the dominant fungal phylum. Its abundance increased significantly, from 60.00% in swamp meadow to 72.26% in steppe meadow. The relative abundances of Pathotroph and Saprotroph fungal functions increased with successional stages, while Symbiotroph did not change significantly. Soil ammonium nitrogen and organic carbon levels dominated the effect on the soil fungal microbial community and functional groups.ConclusionThese findings indicate that the fungal community shifted dramatically in the first stage(swamp to alpine meadow) of succession but then reached a relatively stable state in the second(alpine to steppe meadow) successional stage. The soil fungal function group did not follow the same successional trajectory. Soil ammonium nitrogen and soil organic carbon levels imposed the strongest influence on the fungal community and its function, respectively.

Changes of endophytic microbial community in Rhododendron simsii roots under heat stress and its correlation with leaf physiological indicators.

The response mechanism of Rhododendron simsii and its endophytic microorganism to heat stress is still unclear. The light incubator was used to set the temperature gradients, and the control (CK) was (day/night: 14/10 h) 25/22°C, the moderate-heat-stress (MHS) was 35/30°C and the high-heat-stress (HHS) was 40/35°C. Compared with CK, MHS significantly increased the contents of malondialdehyde, hydrogen peroxide, proline, and soluble sugar, as well as the activities of catalase and peroxidase in leaf, while HHS increased the activities of ascorbate peroxidase, and decreased chlorophyll content. Compared with CK, MHS reduced soil available nitrogen (N) content. Both heat stress changed the endophytic microbial community structure in roots. MHS enriched Pezicula and Paracoccus, while HHS significantly enriched Acidothermus and Haliangium. The abundance of Pezicula positively correlated with the contents of chlorophyll a and proline in leaf, and negatively correlated with soil ammonium N content. The abundance of Pezicula and Haliangium positively correlated with soluble sugar and malondialdehyde contents, respectively. Our results suggest that root endophytic microorganisms play an important role in helping Rhododendron resisting heat stress, mainly by regulating soil N content and plant physiological characteristics.

Brachiaria humidicola Cultivation Enhances Soil Nitrous Oxide Emissions from Tropical Grassland by Promoting the Denitrification Potential: A 15N Tracing Study

Biological nitrification inhibition (BNI) in the tropical grass Brachiaria humidicola could reduce net nitrification rates and nitrous oxide (N2O) emissions in soil. To determine the effect on gross nitrogen (N) transformation processes and N2O emissions, an incubation experiment was carried out using 15N tracing of soil samples collected following 2 years of cultivation with high-BNI Brachiaria and native non-BNI grass Eremochloa ophiuroide. Brachiaria enhanced the soil ammonium (NH4+) supply by increasing gross mineralization of recalcitrant organic N and the net release of soil-adsorbed NH4+, while reducing the NH4+ immobilization rate. Compared with Eremochloa, Brachiaria decreased soil gross nitrification by 37.5% and N2O production via autotrophic nitrification by 14.7%. In contrast, Brachiaria cultivation significantly increased soil N2O emissions from 90.42 μg N2O-N kg−1 under Eremochloa cultivation to 144.31 μg N2O-N kg−1 during the 16-day incubation (p < 0.05). This was primarily due to a 59.6% increase in N2O production during denitrification via enhanced soil organic C, notably labile organic C, which exceeded the mitigated N2O production rate during nitrification. The contribution of denitrification to emitted N2O also increased from 9.7% under Eremochloa cultivation to 47.1% in the Brachiaria soil. These findings confirmed that Brachiaria reduces soil gross nitrification and N2O production via autotrophic nitrification while efficiently stimulating denitrification, thereby increasing soil N2O emissions.

Long-acting mechanisms of concentrated urea application — High urea concentrations are biological inhibitors

The concentrated application of urea (CAU; including band and hole placements) promotes cereal crop (e.g., rice and summer maize) yields and nitrogen (N) use efficiency by prolonging the retention of N fertilizer in the soil and reducing N loss. However, the long-acting mechanisms of CAU are not well understood. This study investigated the interactions between N transformation and soil microbes in the special micro-region around the fertilization point with the CAU, using a simulation experiment with two types of soil (silty loam and sandy loam). The soil samples were subjected to six N treatments: 1000, 3000, 5000, 10,000, 30,000 mg N kg−1, and dicyandiamide with 1000 mg N kg−1; no urea treatment was a control. Soil bacterial community compositions (examined using MiSeq sequencing), the abundance of ammonia-oxidizing microbes (quantified using real-time PCR), including ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), and the soil chemical properties were assessed at 20 and 60 days after urea application. The high soil ammonium concentration caused by CAU affected the soil bacterial community by changing the soil chemical properties. Soil ammonium concentration and pH were the main factors affecting microbial communities and amoA gene abundance of AOA and AOB. The 10,000 and 30,000 mg N kg−1 dosages for the silty loam soil and 30,000 mg N kg−1 dosage for the sandy loam soil in this simulation experiment significantly (p < 0.05) reduced bacterial α-diversity, amoA gene abundance of AOA and AOB, and inhibited nitrification throughout the culture period. However, the inhibitory effects of high soil N application concentration on nitrification weakened as the culture time increased. Overall, CAU acted as a biological nitrification inhibitor by maintaining high soil ammonium concentration, which decreases activity of AOA and AOB amoaA genes for a long time (>60 days).

Improving Nitrogen Availability and Ananas comosus L. Merr var. Moris Productivity in a Tropical Peat Soil Using Clinoptilolite Zeolite

Pineapple cultivation in nitrogen deficient and acidic peat soils leads to poor growth, yield, and fruit quality of pineapples. A study was conducted to determine whether clinoptilolite zeolite (CZ) could improve soil nitrogen availability, growth, yield, and fruit quality of pineapples grown in drained peat soils. Laboratory leaching experiments were conducted to determine the effectiveness of CZ in controlling nitrogen loss from peat soils, whereas an ion-exchange resin method was used to determine nitrogen availability in pineapple cultivation. Treatments evaluated were: (i) different amounts of CZ (25, 50, 70, and 100%) + NPK fertilizer, (ii) NPK fertilizer, and (iii) peat soil only. The peat soils with CZ reduced ammonium and nitrate losses because of the sorption of ammonium within the lattices of the CZ via ion exchange. Co-application of CZ (25%) and NPK fertilizers was more effective in increasing soil ammonium availability, whereas the use of CZ (25% to 100%) improved nitrogen uptake and use efficiency, growth, yield, and fruit quality of pineapple because CZ could regulate the availability of nitrogen ions for pineapple uptake. The buffering capacity of CZ increased soil pH and facilitated organic nitrogen mineralization. The co-application of CZ and NPK fertilizers can be used to improve nitrogen availability and pineapple productivity in tropical peat soils.

Spatiotemporal distribution of residual ammonium in a rare-earth mine after in-situ leaching: A modeling study with scarce data

The large amount of residual soil ammonium nitrogen (NH4-N) after in-situ leaching is a legacy environmental issue for ionic rare earth mines. Understanding and mitigating the associated risk to the aquatic ecosystems of the mining as well as its downstream areas would benefit from a quantitative description and prediction of NH4-N transformation and transport during and after in-situ leaching. Up to date, studies related to the transport and leaching characteristics of residual soil NH4-N have been mostly limited to laboratory experiments. Few field process-based studies of the transport behaviors of residual leaching agents in rare earth mines have been conducted partially because of their remote locations, restricted accessibility, and scarce background data. Based on field investigations at a remote hilly rare earth mine in Ganzhou City, Southern China, we established a HYDRUS-2D model to simulate the transport and transformation of soil NH4-N in the mine throughout in-situ leaching, flushing, and subsequent rainwater leaching. Though subjected to conceptual generalization and limited background data, the established HYDRUS-2D model was able to satisfactorily simulate the observed distinctively different vertical soil NH4-N and nitrate nitrogen (NO3-N) profiles at the top, middle, and bottom of the hill in March 2021, with R2 ranging from 0.71 to 0.89 for soil NH4-N and 0.69 to 0.86 for soil NO3-N. Further analysis of the HYDRUS simulation results revealed a much different spatiotemporal distribution pattern between soil NH4-N and NO3-N throughout the simulation period. For soil NH4-N, the shape and spatial extent of its distribution was largely determined by in-situ leaching, whereas flushing and rainwater leaching slowly pushed its spatial extent further downward, and to a less extent downslope to the right. Flushing and five years of rainwater leaching could merely remove around 10% of residual soil NH4-N from the hill. Unlike NH4-N, the spatial distribution pattern of soil NO3-N varied considerably among various phases of in-situ leaching, flushing, and rainwater leaching. Soil water movement affected the spatial distribution of soil NO3-N considerably, which was especially evident from its significant buildup near surface at the bottom of the hill. Overall, our study results have revealed the critical role of continuous water movement and solute transport in shaping the distribution patterns of residual leaching agents in rare earth mining regions. The proposed HYDRUS model may serve as a promising framework for investigating the transport and spatiotemporal distribution of in-situ leaching agent in rare earth mining regions with scarce background data. It also has great potentials in facilitating the development of more effective in-situ leaching programs and the design of suitable water pollution control and ecological remediation measures.

Effects of Bacillus subtilis and Pseudomonas fluorescens as the soil amendment

The application of soil beneficial bacteria (SBB) in agriculture is steadily increasing as it provides a promising way to replace chemical fertilisers and other supplements. Although the role of SBB as a biofertiliser is well understood, little is known about the response of soil physiochemical properties via the change in soil enzymatic activities with SBB growth. In this study, sterilised bulk soil was inoculated with Bacillus subtilis (BS) and Pseudomonas fluorescens (PF), which exhibit excellent characteristics in vitro for potentially improving soil quality. It is found that the contents of bioavailable nitrogen and ammonium in soil inoculated with SBB increased significantly, up to 34% and 57% relative to a control. This resulted from the enhancement of soil urease activity with BS and PF treatments by approximately 90% and 70%, respectively. The increased soil urease activity can be explained by the increased microorganism activity evident from the larger population size of BS (0.78–0.97 CFU mL−1/CFU mL−1) than PF (0.55–0.79 CFU mL−1/CFU mL−1) (p < 0.05). Results of principal component analysis also reinforce the interaction apparent in the significant relationship between soil urease activity and microbial biomass carbon (p < 0.05). Therefore, it can be concluded that the enhancement of soil enzymatic activities induced bulk soil fertility upregulation because of bacterial growth. These results demonstrate the application of SBB to be a promising strategy for bulk soil amendment, particularly nutrient restoration.

Bacterial Community Shifts in Casing Soil Before and After the Cultivation of Oudemansiella raphanipes

Casing soil is a key step in the production of Oudemansiella raphanipes. Bacterial community in casing soil plays key roles in the growth and development of edible fungi. However, a knowledge gap remains regarding the bacterial community shifts in casing soil before and after the cultivation of O. raphanipes (CSBACO). Casing soil samples before and after the cultivation of O. raphanipes (CSBC and CSAC) were collected and examined by high-throughput 16S rRNA gene sequencing technology. Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were dominant phyla in casing soil of O. raphanipes, which accounted for 77.32% of the total abundance. After the cultivation of O. raphanipes, the alpha diversity of bacterial community and the relative abundance of some beneficial genera such as Marmoricola, Nocardioides, Sphingomonas, and Streptomyces decreased, while that of bacteria belonging to the candidate class MB-A2-108 tolerant to adverse environment significantly increased. Meanwhile, physicochemical properties of casing soil changed significantly in CSBACO. Soil ammonium nitrogen and organic matter greatly decreased in CSAC and they mainly influenced bacterial community before the cultivation of O. raphanipes. In contrast, available potassium and pH significantly increased in CSAC and mainly affected bacterial community after the cultivation of O. raphanipes. Furthermore, the relative abundance of bacteria with the function of amino acid and lipid metabolism decreased, while that of bacteria functions related to parasites and pathogens increased, which further revealed the significance of bacterial community in casing soil. Diversity, composition, and the potential function of bacterial community shifted dramatically in CSBACO. The results deepen the understanding of the bacterial community and its microecological mechanism in casing soil of O. raphanipes.

Nitrogen and Phosphorus Fertilization Reshapes the Abundance and Structure of Ammonia Oxidizers on a Leymus chinensis Steppe in Northern China

Although nitrogen (N) and phosphorus (P) fertilization are important for maintaining the health and productivity of Leymus chinensis steppe, their impact on the abundance and community structure of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in this ecosystem is still unclear. We used the amoA gene as a molecular marker to monitor changes in AOA and AOB under low and high N and P fertilization and applied the resin-core technique to measure soil N mineralization. We found that the abundance of AOA based on amoA gene copies, ranging from 7.51 × 107 to 1.23 × 108 copies g−1 soil, was higher than that of AOB. Fertilization, especially high N and P, increased the number of amoA copies associated with AOB. AOA and AOB communities were dominated by Crenarchaeota and Proteobacteria, respectively. Fertilization decreased the relative abundances of Thaumarchaeota in the AOA community and Proteobacteria in the AOB community and increased the relative abundance of Ammonia_oxidizing_bacteria_ensemble. In N and P fertilization treatments, soil N transformation was closely related to AOB but not AOA. Soil ammonium N and nitrate N reshape the structure of ammonia oxidizers of AOB but not those of AOA on L. chinensis steppes.

Fire shifts the soil fertility and the vegetation composition in a natural high-altitude grassland in Brazil

The Serra da Calçada Mountain (Minas Gerais State, Brazil) hosts a natural grassland with high biodiversity and endemism, locally known as campo rupestre, which grows over hematite and quartzite outcrops, protecting several headwaters. However, this mountain has been severely threatened by anthropogenic fires and its restoration has been challenged by the lack of knowledge on the effect of fire on plant species and soil fertility. Thus, this study aimed to assess a burned campo rupestre site after 1 year concerning plant biodiversity and soil properties as compared to a preserved site. Aside from the high plant biodiversity, the preserved site (with no fire history) showed a high natural soil fertility, particularly regarding soil organic matter (SOM): ∼3.48%, Cationic Exchange Capacity (CEC): ∼8.4 meq/100g, soil ammonium (NH4+-N): ∼11 ppm and soil phosphorus (P): ∼6.9 mg/Kg. However, the fire reduced not only the plant species composition, abundance, richness and biodiversity, but also disrupted the natural soil fertility. There was a change in N chemical species from ammonium to nitrate as well as an increase in sodium (Na) content, in addition to a depletion of SOM and CEC. The variations of nitrogen chemical species, sodium, SOM, CEC and soil moisture explained 79% of the changes in plant composition as revealed by the Mantel matrix permutation test. Increased soil nitrate and sodium were considered the main factors determining changes in vegetation composition after fire. Therefore, fires should be strictly avoided for the management of the campo rupestre grassland, and for the rehabilitation purposes, the improvement of SOM and ammonium in detriment of nitrate is recommended.

Earthworms regulate the nematode community by directly enhancing the bacterial-based energy channel rather than through the effect of casts

Earthworms and their casts act as biocatalysts and regulators of the biotic and abiotic processes in soil ecosystems. However, the relative importance of the presence of earthworms and earthworm casts in affecting other soil biota remains underexplored. In this study, we conducted a manipulative mesocosm experiment in a 30-year-old subtropical broadleaved plantation forest to determine how epi-endogeic earthworms (Amynthas corticis) and their casts affect soil nematode communities individually and additively. We found that the addition of the epi-endogeic earthworms significantly increased the proportion of the Ba1 guild nematodes and enhanced the enrichment index of the soil nematode community, but decreased the channel index. These results indicate that the soils become enriched in nutrients with a higher activity in bacterial-based decomposition pathways in the presence of earthworms. However, cast addition alone had a minor effect on soil nematodes. Results of a redundancy analysis suggest that elevated contents of soil ammonium and available phosphorous were the major influencing factors on soil nematode abundances in the presence of epi-endogeic earthworms. Our results indicate that epi-endogeic earthworms rather than through their casts contributed to the structuring of the nematode communities and enhancing of the bacterial-based energy channel. This finding contributes to our understanding of soil biodiversity maintenance mechanisms and how the relationship of the soil biota affects their functions in soil food webs.

Hydrothermal Changes and Physicochemical Characteristics of Subtropical Subalpine Soils under Freezing and Thawing

The soil column samples were collected for indoor simulated freeze-thaw experiments to monitor the soil hydrothermal dynamics and measure the basic physicochemical properties to research the effects of freeze-thaw on the hydrothermal process of peat bog soil and its relationship with physicochemical properties. The results indicate that in the initial phase of freezing-thawing, soil water content decreases and soil temperature changes, respectively. Unfrozen water content in soil in the stable freezing period decreases sharply. Compared with the freezing period, the fluctuation of soil moisture rate during thawing is more moderate with the temperature change. Soil ammonium nitrogen content decreases with decreasing soil temperature and is significantly positively correlated with soil water content after freeze-thaw, while total phosphorus, fast-acting phosphorus, total nitrogen and nitrate have no significant correlation with soil temperature and soil moisture content after freeze-thaw.

Short-term but not long-term perennial mugwort cropping increases soil organic carbon in Northern China Plain.

Perennial cropping has been an alternative land use type due to its widely accepted role in increasing soil carbon sequestration. However, how soil organic carbon (SOC) changes and its underlying mechanisms under different cropping years are still elusive. A chronosequence (0-, 3-, 6-, 20-year) of perennial mugwort cropping was chosen to explore the SOC dynamics and the underlying mechanisms in agricultural soils of Northern China Plain. The results revealed that SOC first increased and then decreased along the 20-year chronosequence. The similar patterns were also found in soil properties (including soil ammonium nitrogen, total nitrogen and phosphorus) and two C-degrading hydrolytic enzyme activities (i.e., α-glucosidase and β-glucosidase). The path analysis demonstrated that soil ammonium nitrogen, total nitrogen, and plant biomass affected SOC primarily through the indirect impacts on soil pH, total phosphorus availability, and C-degrading hydrolytic enzyme activities. In addition, the contributions of soil properties are greater than those of biotic factors (plant biomass) to changes in SOC across the four mugwort cropping years. Nevertheless, the biotic factors may play more important roles in regulating SOC than abiotic factors in the long run. Moreover, SOC reached its maximum and was equaled to that under the conventional rotation when cropping mugwort for 7.44 and 14.88 years, respectively, which has critical implications for sustainable C sequestration of agricultural soils in Northern China Plain. Our observations suggest that short-term but not long-term perennial mugwort cropping is an alternative practice benefiting soil C sequestration and achieving the Carbon Neutrality goal in China.

Adsorption of ammonium ions onto the external surface of smectite: Effects of layer charge, concentration, anion and comparison with interlayer adsorption

The residual and release of ammonium in ion-adsorption rare earth tailings and soil are related to the interaction of NH4+ with clay minerals. Molecular dynamics simulations were used to study the adsorption and diffusion of NH4+ on the external surface of smectite. The factors, such as layer charge position (octahedral and tetrahedral substitution) and charge density (0.5, 1.0 and 1.5 e⋅uc−1, where uc denotes unit cell), initial NH4+ concentration (from 0.64 to 1.60 mol⋅L−1), and anion types (Cl−, NO3− and SO42−) were considered. The results of NH4+ adsorption on the external surface were also compared with that in the interlayer. The layer charge of smectite significantly affected the interaction between NH4+ and smectite. With increasing charge density, the major NH4+ surface complexes were changed from outer-sphere to inner-sphere, resulting in increased adsorption density and stability, which was verified by calculated hydration structure and adsorption free energies. The inner-sphere NH4+ complexes were located above the centers of the hexagonal rings and the Si tetrahedras for montmorillonite at a charge density of 1.0 e⋅uc−1, while only located in the vicinity of tetrahedral substitutions for beidellite. NO3− promoted the adsorption of NH4+ as inner-sphere complexes relative to Cl− and SO42−. As the water content in the interlayer increased, the confinement effect weakened and the mobility of NH4+ increased, and the NH4+ adsorption in the interlayer exhibited similar characteristics to that on the external surface at a water content of 10 H2O⋅uc−1.

Effects of flooding outweigh those of vegetation restoration on key processes of carbon and nitrogen cycling in a degraded riparian zone

Active revegetation (AR) and natural regeneration (NR) are two restoration approaches widely used to rehabilitate degraded riparian ecosystems, which are subjected to frequent hydrological fluctuations owing to climate change and human activities. Nevertheless, the impacts of restoration approaches and hydrological changes on the key processes of carbon and nitrogen cycling, particularly in degraded riparian ecosystems, remain unclear. In this study, we conducted hydrological experiments, which began in 2016, at three flooding zones (extreme flooding zone, severe flooding zone, and moderate flooding zone) of AR and NR areas in the Three Gorges Reservoir to investigate the effects of restoration approach and hydrological changes on soil properties, vegetation diversity, microbial characteristics, denitrification rates, and greenhouse gas fluxes. The results showed that compared with NR, AR did not change vegetation diversity, microbial diversity, and soil denitrification rates, but decreased soil ammonium and total carbon contents. The vegetation coverage of each flooding zone was more than 90%, and vegetation diversity was relatively high in the moderate flooding zone. Moreover, the maximum denitrification rates and CO2 fluxes were observed in the extreme flooding zone along with a high soil nutrient content. Additionally, the effect of flooding zone superseded the impacts of restoration approaches since AR could only significantly increase the CO2 flux (p < 0.05). Overall, this study elucidates the impacts of restoration approaches and hydrological changes on C and N cycling, and aids in developing restoration strategies for degraded riparian ecosystems.

Microflora for improving the Auricularia auricula spent mushroom substrate for Protaetia brevitarsis production

SummaryMushroom cultivation is a sustainable agricultural waste utilization method, but the lack of high-value utilization of the produced spent mushroom substrate (SMS) has hindered the development of mushroom cultivation-based circular agricultural systems. Conversion and utilization of SMS via Protaetia brevitarsis larvae (PBL) have proven to be a high-value AASMS utilization strategy. However, Auricularia auricula SMS (AASMS), which contains woodchips, is less palatable and digestible for PBL. To solve this problem, in this investigation, we screened out microflora (MF) for AASMS fermentation by comparing the fermentation performance as well as the effect on PBL feed intake, weight gain, and AASMS phytotoxic compound removal efficiency. In addition, by bacterial community analysis, the genera Luteimonas, Moheibacter, and Pseudoxanthomonas were predicted to be functional bacteria for AASMS fermentation and contribute to palatability and digestibility improvement.