Soil Ammonium Research Articles

ASSERT: A Platform Technology for Rapid Electrochemical Sensing of Soil Ammonium.

The world is facing a food shortage predicament largely fueled by inefficient, outdated farming conventions that are passed down from generation to generation. Overfertilization is one of the major byproducts of inadequate farming techniques. This leads to an imbalance in the soil ecosystem, affecting carbon sequestration, plant-available nutrients, and microorganisms. Sustainable agriculture, on the other hand, efficiently uses the soil with minimal fertilizer and crop rotation to prevent soil erosion. This method requires real-time information on the soil's health. An electrochemical ion-selective electrode (ISE) is presented to measure soil ammonium in situ. The sensor utilized electrochemical impedance spectroscopy for direct, continuous soil ammonium measurement without any soil pretreatment. The ISE is applied by drop-casting onto the working electrode. The sensor response was calibrated against the three main different soil textures (clay, sandy loam, and loamy clay) to cover the entirety of the soil texture triangle. The linear regression models showed an ammonium-dependent response with Pearson r > 0.991 for the various soil textures in the range of 2-32 ppm. The sensor response was validated against the gold standard spectrophotometric method after KCl extraction showed a less than 20% error rate between the measured ammonium and reference ammonium. A 16 day in situ soil study showed the capability of the sensor to measure soil ammonium in a temporally dynamic manner with a coefficient of variance of 11%, showing robust stability for in situ monitoring.

Conversion of coastal marsh to aquaculture ponds altered soil ammonia oxidiser community and decreased ammonia oxidation potential

AbstractIntroductionAs a crucial component of the nitrogen cycle, ammonia oxidation in soil can be driven by canonical ammonia‐oxidising archaea (AOA) and bacteria, as well as complete ammonia oxidiser (CMX Nitrospira). Land use change can disrupt and alter the soil microbial community and the nitrogen cycle.Materials & MethodsWe compared the soil ammonia‐oxidising microorganisms and ammonia oxidation potentials in a coastal marsh and nearby reclaimed aquaculture ponds, monthly over a 10‐month period in southeastern China. The abundance of ammonia oxidisers was assessed by real‐time quantitative PCR and the community structure of CMX Nitrospira was evaluated by high‐throughput sequencing.ResultsThe ammonia oxidiser community was dominated by AOA in the marsh (91%) and was made up of similar proportions of AOA and CMX Nitrospira in the aquaculture ponds (46%–47%). The CMX Nitrospira community structure changed significantly between habitat types, mainly driven by opposite change in relative abundance of clade B versus clades A.2 and A.3. Aquaculture reclamation decreased the soil potential ammonia oxidation rate (PAO) by an order of magnitude, and AOA was the only significant predictor of PAO among all ammonia oxidiser groups.ConclusionOur results suggest that aquaculture reclamation from coastal marshes would significantly alter the soil ammonia oxidiser community and decrease ammonia oxidation rate, and CMX Nitrospira appear to play a relative larger role in nitrogen cycling in aquaculture ponds.

Green manure combined with reduced nitrogen reduce NH3 emissions, improves yield and nitrogen use efficiencies of rice

Background Green manure is an important source of organic fertilizer. Exploring green fertilizer and nitrogen fertilizer reduction is important for agricultural production. However, few studies have been conducted, especially on the effects of different green fertilizers along with reduced nitrogen fertilizer application on soil ammonia volatilization emissions, rice yield, and nitrogen fertilizer uptake and utilization. Methods In this study, the effects of different types of green manure and reduced nitrogen fertilizer application on soil ammonia volatilization emissions, aboveground population characteristics of rice, and nitrogen fertilizer uptake and utilization were explored. This study was based on a field-positioning experiment conducted between 2020 and 2022. Six treatments were established: no nitrogen fertilizer application (CK), conventional fertilization in wheat-rice (WR), villous villosa-rice (VvR), vetch sativa-rice (VsR), rapeseed seed-rice (RR), and milk vetch-rice (GR), with a 20% reduction in nitrogen fertilizer application. The amounts of phosphorus and potassium fertilizers remained unchanged. The characteristics of ammonia volatilization loss in rice fields, agronomic traits of rice, yield traits, and nitrogen uptake and utilization were investigated. Results The results indicated a significant difference (P < 0.05) in the impact of different treatments on ammonia volatilization emissions from rice in the two-year experiment. Compared with WR treatment, VvR, VsR, RR, and GR treatments reduced the total ammonia volatilization loss by 23.58 to 39.21 kg ha−1, respectively. Compared with the conventional WR treatment, other treatments increased rice yield by 0.09 to 0.83 t ha−1. GR treatment was significantly higher than other green fertilizer treatments, except for VsR (P < 0.05). It increased the nitrogen uptake of rice by an average of 4.24%–22.24% and 13.08%–33.21% over the two years, respectively. The impact of different types of green manure on the nitrogen uptake and utilization of rice varied greatly, indicating that the combination of green manure and fertilizer is a sustainable fertilization model for crops to achieve high yields. In particular, the Chinese milk vetch as green manure was more beneficial for ammonia volatilization reduction in paddy field and stable grain production of rice.

Optimizing the Nitrogen Fertilizer Management to Maximize the Benefit of Straw Returning on Early Rice Yield by Modulating Soil N Availability

Straw returning has gradually been adopted as an effective approach to address the serious degradation of farmland. However, the carbon/nitrogen (C/N) ratio of rice straw is generally too high for microorganisms to decompose the organic materials and release nutrients, which may minimize the benefits of straw returning to the agricultural production system. This study aimed to investigate the effects of straw returning on rice production and propose optimum nitrogen (N) management for early rice production under a straw returning system. The total N fertilizer that was evaluated was 165 kg N ha-1, urea (46% N), applied in different proportions in three stages of rice cultivation: basal, tillering, and panicle. Using no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment (T1) as the control, four different N fertilizer ratios of basal:tillering:panicle, including 5:2:3 (T2), 5:2:2 (T3), 5:4:1 (T4), and 5:5:0 (T5) were set under straw returning. The return of straw decreased the available N in the soil at the tillering stage, and impeded root growth and the crop canopy from establishing, which decreased the effective panicles by 10.1% compared with that of T1, limiting the increases in rice grain yield. Increasing the N fertilizer ratio 10–20% (T3 and T4) at the tillering stage effectively increased the content of soil ammonium and nitrate nitrogen, improved the root growth, and increased the root activities by 16.0–40.5% at the tillering stage. As a result, the effective panicle number increased by 5.1–16.2%. Among these, T4 treatment maximized the benefits of straw returning the most. Additionally, increasing the N fertilizer ratio at the tillering stage increased the shoot uptake across the early rice growing season and synchronized crop N uptake with the accumulation of carbon assimilates, which enhanced the crop growth rate and increased the rice yield by 13.5–25.1%. It is concluded that increasing the N fertilizer ratio by 20% at the tillering stage is a promising strategy to increase the availability of N in the phases of high demand for this nutrient.

Effects of Straw Return and Nitrogen Application Rates on Soil Ammonia Volatilization and Yield of Winter Wheat

This study investigates the impact of corn straw return and nitrogen application rates on ammonia volatilization and yield enhancement under field conditions, in order to reduce emissions while increasing crop yield. During the winter wheat season, a fissure area design was implemented, comprising three levels of straw return in the main area and three distinct nitrogen fertilizer levels in the subsidiary area, for a total of nine treatments. The results can be summarized as follows: (1) The ammonia emissions flux initially increased followed by a decrease, and was primarily concentrated within the first 14 days after fertilization, with a peak observed at 4–5 days before decreasing. Notably, nitrogen fertilizer significantly affected the cumulative ammonia emissions, ranging from 0.019 to 1.786 kg·hm−2·d−1 and 0.013 to 1.693 kg·hm−2·d−1 across the two seasons. (2) The soil with a higher nitrogen application rate exhibited elevated levels of inorganic nitrogen content and urease activity under the same straw return level. Maintaining a consistent nitrogen application level, the return of straw to the field increased the cumulative ammonia discharge, inorganic nitrogen content, and urease activity. (3) The interaction between straw return and nitrogen fertilizer substantially affected crop yield. Specifically, during the winter wheat season, the optimal combination for reducing ammonia emissions and enhancing yield was observed under straw return (both half or full) combined with 180 kg·hm−2 nitrogen application. Notably, the reduction of soil emissions and winter wheat yield augmentation were feasible through appropriate corn straw return in the preceding season.

PBAT microplastics exacerbates N2O emissions from tropical latosols mainly via stimulating denitrification

Biodegradable plastic mulching films are regarded as promising substitutes for their non-degradable counterparts to ameliorate serious plastic pollution in agriculture. Inevitably, biodegradable microplastics (BMs) can be formed and profoundly affect the function of soil ecosystems. However, little is known about the effects of BMs loading on soil nitrogen (N) dynamics and loss in tropical agricultural soils. Hereby, a 120-day soil incubation trial was performed to evaluate the effects of polybutylene adipate co-terephthalate (PBAT) microplastics on nitrous oxide (N2O) emissions, N transformation, and bacterial community structure in latosols. The results showed that PBAT addition raised soil ammonium nitrogen (NH4+–N) and dissolved organic carbon (DOC) contents, but lowered nitrate nitrogen (NO3––N) contents, accompanied with a smaller potential nitrification rate and a greater potential denitrification rate. The microbial biomass nitrogen and nrfA gene abundance were increased by PBAT, suggesting the processes of microbial N immobilization and dissimilatory nitrate reduction to ammonia were largely promoted. Positive correlations existed between N2O emissions and denitrification-related enzymatic activities and functional gene abundances (narG, nirK/S and Fungal nirK). PBAT amendment stimulated N2O emissions by 54.8 − 317.3 %, accompanied with increased values of those denitrification-related parameters, suggesting that stimulated denitrification was responsible for the exacerbated N2O emissions. Moreover, PBAT addition changed bacterial alpha diversity and bacterial community composition, where the relative abundances of Proteobacteria increased while those of Nitrospirae and Acidobacteria decreased. These findings are beneficial to understanding the fate of N in microplastics-polluted soil, which will provide a new insight into the impact of BMs on soil functions and environmental risks.

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

Effects of the nitrification inhibitor nitrapyrin on N2O emissions under elevated CO2 and rising temperature in a wheat cropping system

Nitrogen (N) fertilizer input will likely increase to meet the food demands of a growing population under climate change conditions, characterized by increasing atmospheric CO2 concentration and temperature. Nitrification inhibitors have the potential to reduce N2O emissions from N fertilized croplands. However, it remains unclear whether future climate change scenarios could affect the effectiveness of nitrification inhibitors. In a two-year study, winter wheat (Triticum aestivum L.) was cultivated in climate-controlled growth chambers with an elevated CO2 concentration (ambient +200 μmol mol−1) and increased temperature (ambient +2 °C). Urea was applied with or without nitrapyrin (0.5 % of urea-N). In this study, we measured nitrous oxide (N2O) fluxes, soil ammonium and nitrate levels, and the abundance of five nitrogen-cycling genes related to nitrification (amoA of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA)) and denitrification (nirS, nirK and nosZ). Key findings included the following: 1) without nitrapyrin, cumulative N2O emissions were not significantly altered by increased temperature, but decreased 24.9 % by the combination of elevated CO2 and temperature treatment and 17.5 % by the elevated CO2 alone. NO3−-N accumulation occurred in soils under increased CO2 and temperature, both individual and in combination; 2) nitrapyrin effectively reduced AOB abundance, inhibiting NO3−-N accumulation and N2O emission, irrespective of CO2 concentrations and temperature. However, under the combination of elevated CO2 and temperature conditions, the efficiency of nitrapyrin in reducing N2O emission was lower (−13 % to −49 %) than that in the control (−28 % to −65 %) and elevated CO2 (−32 % to −71 %) conditions. This reduced effectiveness of the combined treatment can be attributed to the inability of nitrapyrin to inhibit the AOA, nirS and nirK genes. Thus, nitrapyrin is expected to reduce N2O emissions under future climate change scenarios, but the efficacy may be lower than previously expected when CO2 concentration and temperature increase simultaneously. The indirect effects of nitrapyrin on denitrifiers under climate change scenarios should be considered in future research.

15N mass balance technique for measuring ammonia losses from soil surface‐applied slurries containing various additives

AbstractBackgroundAnthropogenic ammonia emissions, primarily derived from agriculture, lead to air pollution, soil acidification, and surface water eutrophication, all of which adversely affect human health and ecosystems. Slurry treatment technologies in the form of additives represent an underutilized means of reducing gaseous emissions. Information regarding the potential of additives to reduce ammonia in soil surface‐applied slurries is scarce.AimThis study aims to develop a 15N mass balance technique to quantitatively measure ammonia losses from different slurries containing multiple additives that are applied to outdoor soil‐filled containers.MethodsThe experiments were performed under free‐air conditions. Isotopically labeled slurries from biogas, cattle, and pigs containing 18 additives were surface‐applied to soil‐filled containers and exposed for 72 or 48 h. The additives included inorganic and organic adsorbents, five amounts of sulfuric acids, molasses ± effective microorganisms, and water dilution. After termination of the ammonia loss period, a suite of soil preparation steps for the quantitative recovery of the labeled ammonium remaining in the soil was developed, and subsequently the loss of NH4‐N was determined.ResultsIn the control treatments, ammonia losses from biogas, cattle slurries, and pig slurries averaged 54.4%, 33.9%, and 11.0%, respectively. The adsorbents did not decrease or only slightly decreased ammonia emissions. Ammonia abatement by sulfuric acid was nearly complete at pH values of 5.9 and 5.8 for the biogas and pig slurry, respectively, and about 80% at pH 5.2 for the cattle slurry. In comparison, more moderately decreased pH values with sulfuric acid showed a similar reduction as molasses and a 1:1 dilution for the three slurries. Adding microorganisms to the molasses did not further decrease ammonia losses.ConclusionThe newly developed 15N mass balance technique, which allows a precise estimate of ammonia losses, can serve as a reference method to assess ammonia losses from field‐applied slurries containing various additives and as a standard comparison technique for other ammonia measurement techniques.

Soil Acidification Can Be Improved under Different Long-Term Fertilization Regimes in a Sweetpotato-Wheat Rotation System.

Soil acidification is a significant form of agricultural soil degradation, which is accelerated by irrational fertilizer application. Sweetpotato and wheat rotation has emerged as an important rotation system and an effective strategy to optimize nutrient cycling and enhance soil fertility in hilly areas, which is also a good option to improve soil acidification and raise soil quality. Studying the effects of different fertilization regimes on soil acidification provides crucial data for managing it effectively. An eight-year field experiment explored seven fertilizer treatments: without fertilization (CK), phosphorus (P) and potassium (K) fertilization (PK), nitrogen (N) and K fertilization (NK), NP fertilization (NP), NP with K chloride fertilization (NPK1), NP with K sulfate fertilization (NPK2), and NPK combined with organic fertilization (NPKM). This study focused on the soil acidity, buffering capacity, and related indicators. After eight years of continuous fertilization in the sweetpotato-wheat rotation, all the treatments accelerated the soil acidification. Notably, N fertilization reduced the soil pH by 1.30-1.84, whereas N-deficient soil showed minimal change. Organic fertilizer addition resulted in the slowest pH reduction among the N treatments. Both N-deficient (PK) and organic fertilizer addition (NPKM) significantly increased the soil cation exchange capacity (CEC) by 8.83% and 6.55%, respectively, compared to CK. Similar trends were observed for the soil-buffering capacity (pHBC). NPK2 increased the soil K+ content more effectively than NPK1. NPKM reduced the sodium and magnesium content compared to CK, with the highest magnesium content among the treatments at 1.60 cmol·kg-1. Regression tree analysis identified the N input and soil magnesium and calcium content as the primary factors influencing the pHBC changes. Structural equation modeling showed that the soil pH is mainly influenced by the soil ammonium N content and pHBC, with coefficients of -0.28 and 0.29, respectively. Changes in the soil pH in the sweetpotato-wheat rotation were primarily associated with the pHBC and N input, where the CEC content emerged as the main factor, modulated by magnesium and calcium. Long-term organic fertilization enhances the soil pHBC and CEC, slowing the magnesium reduction and mitigating soil acidification in agricultural settings.

Effects of Different Forms of Nitrogen Addition on Soil Physical and Chemical Properties and Microbial Community Structure of Perennial Alpine Cultivated Grassland

This study aimed to investigate the impact of different nitrogen forms on soil physicochemical properties and microbial community structure in perennial alpine cultivated grasslands, in order to provide scientific basis for developing nitrogen addition strategies for perennial alpine cultivated grasslands. In June 2022, a 4-year-old Qinghai grassland mixed with Poa pratensis Qinghai and Festuca sinensis Qinghai was established at the Bakatai Farm in Gonghe County, Hainan Tibetan Autonomous Prefecture, Qinghai Province. The study was conducted without fertilization as a control (CK), and three different forms of nitrogen treatments were set up, namely, U:urea (amide nitrogen), A:ammonium sulfate (ammonium nitrogen), and N:calcium nitrate (nitrate nitrogen); the nitrogen application rate for each treatment was 67.5 kg·(hm2·a)-1, and the composition and diversity of soil nutrients and microbial communities under different treatments were analyzed. The results showed that the input of exogenous ammonium nitrogen significantly increased NH4+-N content, AP content, and EC; amide nitrogen input significantly increased SOC content and TN content; and nitrate nitrogen input significantly increased NO3--N content, AN content, and TC content. Exogenous nitrogen input changed the structure of soil bacterial and fungal communities, as well as the relative abundance of dominant phyla and genera, but it did not significantly affect the alpha diversity of bacterial and fungal communities. Principal coordinate analysis (PCoA) showed that different forms of nitrogen addition had a significant impact on the Beta diversity of bacterial communities, whereas the impact on fungal communities was not significant. Redundancy analysis (RDA) indicated that nitrogen addition mainly changed the composition and structure of microbial communities through soil ammonium nitrogen. Overall, ammonium nitrogen fertilizer should be given priority in the soil remediation process of perennial cultivated grasslands in the Qinghai Tibet Plateau.

Divergent effects of single and combined stress of drought and salinity on the physiological traits and soil properties of Platycladus orientalis saplings.

Drought and salinity are two abiotic stresses that affect plant productivity. We exposed 2-year-old Platycladus orientalis saplings to single and combined stress of drought and salinity. Subsequently, the responses of physiological traits and soil properties were investigated. Biochemical traits such as leaf and root phytohormone content significantly increased under most stress conditions. Single drought stress resulted in significantly decreased nonstructural carbohydrate (NSC) content in stems and roots, while single salt stress and combined stress resulted in diverse response of NSC content. Xylem water potential of P. orientalis decreased significantly under both single drought and single salt stress, as well as the combined stress. Under the combined stress of drought and severe salt, xylem hydraulic conductivity significantly decreased while NSC content was unaffected, demonstrating that the risk of xylem hydraulic failure may be greater than carbon starvation. The tracheid lumen diameter and the tracheid double wall thickness of root and stem xylem was hardly affected by any stress, except for the stem tracheid lumen diameter, which was significantly increased under the combined stress. Soil ammonium nitrogen, nitrate nitrogen and available potassium content was only significantly affected by single salt stress, while soil available phosphorus content was not affected by any stress. Single drought stress had a stronger effect on the alpha diversity of rhizobacteria communities, and single salt stress had a stronger effect on soil nutrient availability, while combined stress showed relatively limited effect on these soil properties. Regarding physiological traits, responses of P. orientalis saplings under single and combined stress of drought and salt were diverse, and effects of combined stress could not be directly extrapolated from any single stress. Compared to single stress, the effect of combined stress on phytohormone content and hydraulic traits was negative to P. orientalis saplings, while the combined stress offset the negative effects of single drought stress on NSC content. Our study provided more comprehensive information on the response of the physiological traits and soil properties of P. orientalis saplings under single and combined stress of drought and salt, which would be helpful to understand the adapting mechanism of woody plants to abiotic stress.

Dual inhibitors for mitigating greenhouse gas emissions and ammonia volatilization in rice for enhancing environmental sustainability

The use of inhibitors retain nitrogen as ammonium in soil, giving plants ample time for its uptake. This can reduce nitrous oxide (N2O) emissions, but extended retention may increase ammonia (NH3) volatilization. This study assessed the efficacy of coated urea fertilizers in reducing greenhouse gas (GHG) emissions and NH3 volatilization in rice fields. A field experiment with Pusa 44 rice in the kharif seasons of 2019 and 2020 compared unfertilized control (No N), prilled urea (PU), nitrification inhibitors (NIs): neem oil-coated urea (NCU), karanj oil-coated urea, and dual inhibitor (DI: Limus + NCU). The coated urea fertilizers were analysed with scanning electron microscopy, fourier transform infrared spectrometry, and energy-dispersive spectroscopy. Compared to PU, DI reduced N2O emissions by 23.7%, methane by 11.9%, and NH3 by 29.8%. DI also reduced NH3 emissions by 36–39% compared to other NIs. Overall, DI can lower the global warming potential of rice cultivation in trans Indo-Gangetic plains region by 17.1% for both direct and indirect emissions, suggesting its significant potential to reduce India's contribution to total agricultural GHG emissions.

Grazing decreases net ecosystem carbon exchange by decreasing shrub and semi-shrub biomass in a desert steppe.

Livestock grazing can strongly determine how grasslands function and their role in the carbon cycle. However, how ecosystem carbon exchange responds to grazing and the underlying mechanisms remain unclear. We measured ecosystem carbon fluxes to explore the changes in carbon exchange and their driving mechanisms under different grazing intensities (CK, control; HG, heavy grazing; LG, light grazing; MG, moderate grazing) based on a 16-year long-term grazing experimental platform in a desert steppe. We found that grazing intensity influenced aboveground biomass during the peak growing season, primarily by decreasing shrubs and semi-shrubs and perennial forbs. Furthermore, grazing decreased net ecosystem carbon exchange by decreasing aboveground biomass, especially the functional group of shrubs and semi-shrubs. At the same time, we found that belowground biomass and soil ammonium nitrogen were the driving factors of soil respiration in grazed systems. Our study indicates that shrubs and semi-shrubs are important factors in regulating ecosystem carbon exchange under grazing disturbance in the desert steppe, whereas belowground biomass and soil available nitrogen are important factors regulating soil respiration under grazing disturbance in the desert steppe; this results provide deeper insights for understanding how grazing moderates the relationships between soil nutrients, plant biomass, and ecosystem CO2 exchange, which provide a theoretical basis for further grazing management.

Response of soil inorganic nitrogen dynamics to planting age and vegetation type in artificial sand‐fixing land

AbstractVegetation restoration in dryland regions may be a powerful way to control desertification and promote local habitat recovery. In these artificial revegetation systems, ecosystem processes and functioning are strongly determined by nitrogen (N) availability, while soil inorganic N (SIN) is the major available N form and is absorbed as a main N source for plants. However, SIN dynamics, their influencing factors, and their relative importance to the ecosystem of these N‐limited systems are not well understood. A field investigation was conducted to examine the monthly variations in SIN and its response to planting age and vegetation type in a typical artificial sand‐fixing system in northwestern China. The SIN content in topsoil (0–20 cm) during the growing season ranged from 7.10 to 95.65 mg kg−1, with a mean value of 27.14 mg kg−1. Soil nitrate N had a dominant role in determining SIN monthly dynamics, which showed a fluctuating trend with two peak values in early July and late August. SIN showed a significant increasing trend with the planting age of sand‐fixing vegetation, and it was highest for Nitraria sphaerocarpa (55.66 ± 5.76 mg kg−1), followed by Haloxylon ammodendron (29.81 ± 3.47 mg kg−1) and interspace (11.39 ± 1.13 mg kg−1). SIN displayed a hump‐shaped relationship with air temperature (R2 = 0.96, p < 0.01) and had a maximum at 19.88°C. The change rate of SIN was positively correlated with accumulated precipitation (R2 = 0.99, p < 0.05). SIN was correlated significantly with soil organic carbon (SOC), total nitrogen (TN), and soil clay content. Our results revealed that climatic (air temperature and precipitation), abiotic (soil texture), plant (planting age and vegetation type), and nutrient‐related (SOC and TN) factors regulate SIN dynamics in artificial sand‐fixing vegetation systems. Climate was the predominant factor affecting soil ammonium N, and soil nutrients (SOC and TN) were the predominant factor affecting soil nitrate N. Therefore, these factors should be integrated into optimizing regional vegetation establishment and improving ecosystem management practices in sand‐fixing lands.

Differential responses of temperature sensitivity of greenhouse gases emission to seasonal variations in plateau riparian zones

Riparian zones, regarded as hotspots for greenhouse gas (GHG) emissions, where the variation in temperature sensitivity (Q10) of GHG emissions is crucial for assessing GHG budgets under global warming. However, the seasonal Q10 of GHG emissions from high-elevation riparian zones and underlying microbial mechanisms are poorly documented. This study focuses on seasonal Q10 patterns of GHG emissions from riparian zones along the Lhasa River on the Tibetan Plateau. CO2 and CH4 emissions from riparian soils were more sensitive to temperature in spring than in summer. The opposite trend was observed for Q10 of N2O emissions. Soil organic carbon (SOC) had relatively large direct effects on the Q10-CO2 value in summer, whereas soil nitrate nitrogen (SNO3−-N) was the determinant of Q10-CO2 value in spring. mcrA:pmoA and soil microbial biomass C (SMBC) had strong direct effects on the Q10 of CH4 emissions in summer; the Q10-CH4 value in spring was significantly affected by the mcrA abundance. SMBC and the nirK + nirS abundance were key factors affecting the Q10-N2O value. Q10-CO2 and Q10-CH4 values exhibited strong seasonalities in the lower reaches of riparian soils, mainly due to the seasonalities of SNO3−-N and mcrA:pmoA, respectively. The Q10-N2O value in the middle and upper reaches of riparian soils presented seasonality, which was largely due to the seasonalities of soil ammonia nitrogen and microbial biomass carbon. During thawing, plant productivity increased, substrate carbon was sufficient, microbial biomass increased, and inorganic nitorgen and denitrifier abundance decreased, causing 29.67% and 37.47% decreases in the Q10-CO2 and Q10-CH4 values, respectively, and a 70.85% increase in the Q10-N2O value, indicating that the potential release of N2O from riparian zones along the plateau river was more susceptible to seasonal variations. Our findings are conducive to accurately evaluating the potential contribution of GHG emissions from high-elevation riparian zones to global warming.

Effect of Soil Acidification on Temperature Sensitivity of Soil Respiration

Soil pH significantly impacts microbial activity and community assembly, which in turn determines the temperature sensitivity (Q10) of soil respiration. Due to the high soil acidification in China, it is necessary to understand how soil acidification impacts Q10. Here, the Q10 of soil respiration was examined in a long-term field experiment (1982–present) with different soil pH caused by fertilization management. In this experiment, we selected treatments with neutral pH: (1) no crops and fertilization (CK); (2) crops without fertilization (NF); low pH with (3) crops with chemical fertilization (NPK); and (4) crops with chemical fertilization combined with wheat straw incorporation (WS). Under natural soil temperature changes, we observed that soil acidification lowered the Q10 value of soil respiration. Considering only temperature changes, the Q10 of soil respiration was strongly associated with microbial community composition, alpha diversity, and soil ammonium nitrogen. Considering the interaction between soil pH and temperature, warming strengthened the negative effect of soil pH on the Q10 of soil respiration, and the pathway through which soil pH mediated Q10 included not only microbial community composition, alpha diversity, and biomass but also the soil’s available phosphorus. This work enhanced our insights into the relationships between Q10, temperature, and soil pH by identifying important microbial properties and key soil environmental factors.

Beneficial rhizosphere bacteria provides active assistance in resisting Aphis gossypiis in Ageratina adenophora.

Ageratina adenophora can enhance its invasive ability by using beneficial rhizosphere bacteria. Bacillus cereus is able to promote plant growth and provide a positive feedback effect to A. adenophora. However, the interaction between A. adenophora and B. cereus under the influence of native polyphagous insect feeding is still unclear. In this study, Eupatorium lindleyanum, a local species closely related to A. adenophora, was used as a control, aimed to compare the content of B. cereus in the roots of A. adenophora and rhizosphere soil after different densities of Aphis gossypii feeding, and then investigated the variations in the population of A. gossypii and soil characteristics after the addition of B. cereus. The result showed that B. cereus content in the rhizosphere soil and root of A. adenophora increased significantly under A. gossypii feeding compared with local plants, which also led to the change of α-diversity and β-diversity of the bacterial community, as well as the increase in nitrate nitrogen (NO3 -N) content. The addition of B.cereus in the soil could also inhibit the population growth of A. gossypii on A. adenophora and increase the content of ammonium nitrogen (NH4 +-N) in the soil. Our research demonstrated that B. cereus enhances the ability of A. adenophora to resist natural enemy by increasing soil ammonium nitrogen (NH4 +-N) and accumulating other beneficial bacteria, which means that rhizosphere microorganisms help invasive plants defend themselves against local natural enemies by regulating the soil environment.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12–13% and 13–14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55–0.69 mg/kg), nitrate nitrogen (NO3−-N) (7.02–8.65 mg/kg) contents, and N cycle related enzyme activities (33.47–42.39 μg/h/g) by 37.7–50.9%, 22.6–37.2%, and 34.2–48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Effects of Long-Term Rice–Crayfish Coculture Systems on Soil Nutrients, Carbon Pools, and Rice Yields in Northern Zhejiang Province, China

This research was to examine the impacts of long-term integrated rice–crayfish farming on soil nutrients, carbon pools, and rice yields in paddy fields. The aim was to establish a scientific basis for the sustainable development of RS in the northern region of Zhejiang. The results showed that the change from rice monoculture (CK) to rice–crayfish coculture systems (RS) led to a 24.99% increase in the 5-year average of soil ammonium nitrogen (AN), while the soil nitrate nitrogen (NN), available potassium (AK), and available phosphorus content (AP) decreased by 28.02%, 16.05%, and 28.76%, respectively. Moreover, the total organic carbon (TOC), easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) exhibited a reduction of 2.45%, 8.82%, 35.31%, and 65.84%, respectively. Correlation analysis revealed a significant positive correlation between NN, EOC, and MBC in the RS mode. In terms of rice yield, the 5-year average of rice yield in RS decreased by 8.40% compared to CK. The mean yield of early-maturing rice varieties was reduced by 13.16%, while that of late-maturing rice varieties was reduced by 6.00%. These results shed light on the annual variation in soil nutrients, carbon pools, and rice yield in the RS mode, providing insights for the sustainable development of RS in northern Zhejiang.