Oxygen availability regulates the quality of soil dissolved organic matter by mediating microbial metabolism and iron oxidation

Influence of nitrogen substitution at an equivalent total nitrogen level on bacterial and fungal communities, as well as enzyme activities of the ditch bottom soil in a rice-fish coculture system

BACKGROUND

Rice-fish coculture system (RFS) operates through effectively utilizing water and land resources in a complementary form, but it requires more efficient utilization of fertilizer and feed without compromising rice yield. However, the knowledge of how to regulate the proportion of nitrogen (N) supplied from fertilizer and feed at an equivalent total N level to improve the benefits of RFS remains limited. Therefore, four treatments (S0: RFS with 0% N from fertilizer and 100% N from feed; S25: RFS with 25% N from fertilizer and 75% N from feed; S50: RFS with 50% N from fertilizer and 50% N from feed; S75: RFS with 75% N from fertilizer and 25% N from feed) were conducted to assess the variation of ditch bottom soil properties, microbial communities and enzyme activities, as well as to obtain the optimal ratio of N supplied from fish feed and fertilizer.

RESULTS

The experiments showed that the contents of soil organic matter, total carbon and total N, and the activities of urease, N-acetyl-β-D-glucosaminidase, protease, β-1,4-glucosidase and catalase in the ditch bottom soil significantly reduced in S25 treatment, compared with the other three treatments. Ammonium N content decreased with increasing percentage of the basal fertilizer, whereas nitrate N content and pH value showed an adverse trend. However, the bacterial and fungal communities were unaffected by the ratio shifts between fertilizer-N and feed-N, but their dominant phyla were influenced by the ditch bottom soil N level. Moreover, the bacterial community composition was positively related to nitrate N, whereas fungal diversity was positively correlated with pH, ammonium N and nitrate N, and urease. We also found that the treatment of N input with 25% N from fertilizer and 75% N from feed can reduce N deposition in the ditch bottom soil in the rice-fish coculture system.

CONCLUSION

Our findings indicate that under the equivalent total N input level, the relative higher ratio of N from fish feed increased (S0 treatment) or reduced (S25 treatment) the deposition of N in the ditch bottom soil, and improved fish production, but decreased rice yield; while the higher ratio of N from basal fertilizer increased the transportation of nutrients into the ditch bottom soil and rice yield, but reduced fish production. So when considering multi-balance and multiple benefits, we recommend that a selective substitution ratio within 50% ~ 75% from fish feed to substitute for the basal fertilizer under the equivalent total N input may achieve a good balance of rice and fish production improvement, and reduce nutrients wastage to the ditch bottom, as well as alleviate the potential of non-point source pollution. This study also provides an evidence for regulating and optimizing the ratio of N supplied from fertilizer and fish feed at an equivalent total N level through monitoring the nutrient accumulation in ditch bottom soil in the rice-fish coculture system. © 2024 Society of Chemical Industry.

Seasonal and Spatial Fluctuations of Reactive Oxygen Species in Riparian Soils and Their Contributions on Organic Carbon Mineralization

Reactive oxygen species (ROS) are ubiquitous in the natural environment and play a pivotal role in biogeochemical processes. However, the spatiotemporal distribution and production mechanisms of ROS in riparian soil remain unknown. Herein, we performed uninterrupted monitoring to investigate the variation of ROS at different soil sites of the Weihe River riparian zone throughout the year. Fluorescence imaging and quantitative analysis clearly showed the production and spatiotemporal variation of ROS in riparian soils. The concentration of superoxide (O2•-) was 300% higher in summer and autumn compared to that in other seasons, while the highest concentrations of 539.7 and 20.12 μmol kg-1 were observed in winter for hydrogen peroxide (H2O2) and hydroxyl radicals (•OH), respectively. Spatially, ROS production in riparian soils gradually decreased along with the stream. The results of the structural equation and random forest model indicated that meteorological conditions and soil physicochemical properties were primary drivers mediating the seasonal and spatial variations in ROS production, respectively. The generated •OH significantly induced the abiotic mineralization of organic carbon, contributing to 17.5-26.4% of CO2 efflux. The obtained information highlighted riparian zones as pervasive yet previously underestimated hotspots for ROS production, which may have non-negligible implications for carbon turnover and other elemental cycles in riparian soils.

Spatiotemporal dynamics of dissolved organic matter and disinfection by-products formation potential of Shengzhong Lake in southwest China

The quality and quantity of dissolved organic matter (DOM) in lakes as well as its environmental effects associated with the unintended disinfection by-products (DBPs) have received continuous attention. This work investigated the spatiotemporal dynamics of DOM in Shengzhong Lake in southwest China and the formed DBPs during the chlorine disinfection process. The results showed that lake water in summer had significantly higher dissolved oxygen and dissolved organic carbon than that in winter. In contrast, DOM in winter demonstrated an obviously higher aromaticity and molecular weight than that in summer. Four fluorescence components, i.e., terrestrial humic-like substances (C1), protein-like substances (C2), and microbial humic-like substances (C3 and C4), were identified, and their relative abundance followed in the order of C3 > C4 > C2 > C1 in winter and C4 > C3 > C1 > C2 in summer. The formation potential of trihalomethanes and haloacetic acids in winter was higher and lower than that in summer, which was mainly ascribed to the content of aromatic and hydrophobic substances. Compared to the significant seasonal dynamic, the spatial variation of DOM and the formed DBPs was not obvious. This work sheds light on the spatial-temporal distribution of DOM and the potentially formed DBPs in Shengzhong Lake, and will be helpful for understanding the biogeochemical cycle of carbon and assessing the drinking water safety.

Composition of DOM along the depth gradients in the paddy field treated with crop straw for 10 years

Crop straw return is a widely used agricultural management practice. The addition of crop straw significantly alters the pool of dissolved organic matter (DOM) in agricultural soils and plays a pivotal role in the global carbon (C) cycle, which is sensitive to climate change. The DOM concentration and composition at different soil depths could regulate the turnover and further storage of organic C in terrestrial systems. However, it is still unclear how crop straw return influences the change in DOM composition in rice paddy soils. Therefore, a field experiment was conducted in which paddy soil was amended with crop straw for 10 years. Two crop straw-addition treatments [NPK with 50% crop straw (NPK+1/2S) and NPK with 100% crop straw (NPK + S)], a conventional mineral fertilization control (NPK) and a non-fertilized control were included. Topsoil (0-20 cm) and subsoil (20-40 cm) samples were collected to investigate the soil DOM concentration and compositional structure of the profile. Soil nutrients, iron (Fe) fraction, microbial biomass carbon (MBC), and concentration and optical properties (UV-Vis and fluorescence spectra) of soil DOM were determined. Here, we found that the DOM in the topsoil was more humified than that in the subsoil. The addition of crop straw further decreased the humidification degree of DOM in the subsoil. In crop straw-amended topsoil, microbial decomposition controlled the composition of DOM and induced the formation of aromatic DOM. In the straw-treated subsoil, selective adsorption by poorly crystalline Fe(oxyhydr)oxides and microbial decomposition controlled the composition of DOM. In particular, the formation of protein-like compounds could have played a significant role in the microbial degradation of DOM in the subsoil. Overall, this work conducted a case study within long-term agricultural management to understand the changes in DOM composition along the soil profile, which would be further helpful for evaluating C cycling in agricultural ecosystems.

An Innovative Approach to Alleviate Zinc Oxide Nanoparticle Stress on Wheat through Nanobubble Irrigation

The extensive utilization of zinc oxide nanoparticles in consumer products and the industry has led to their substantial entry into the soil through air and surface runoff transportation, which causes ecotoxicity in agro-ecosystems and detrimental effects on crop production. Nanobubbles (diameter size < 1 µm) have many advantages, such as a high surface area, rapid mass transfer, and long retention time. In this study, wheat seedlings were irrigated with a 500 mg L-1 zinc oxide nanoparticle solution delivered in the form of nanobubble watering (nanobubble-ZnO-NPs). We found that nanobubble watering improved the growth and nutrient status of wheat exposed to zinc oxide nanoparticles, as evidenced by increased total foliar nitrogen and phosphorus, along with enhanced leaf dry mass per area. This effect can be attributed to nanobubbles disassembling zinc oxide aggregates formed due to soil organic carbon, thereby mitigating nutrient absorption limitations in plants. Furthermore, nanobubbles improved the capability of soil oxygen input, leading to increased root activity and glycolysis efficiency in wheat roots. This work provides valuable insights into the influence of nanobubble watering on soil quality and crop production and offers an innovative approach for agricultural irrigation that enhances the effectiveness and efficiency of water application.

Soil organic carbon loss decreases biodiversity but stimulates multitrophic interactions that promote belowground metabolism

Soil organic carbon (SOC) plays an essential role in mediating community structure and metabolic activities of belowground biota. Unraveling the evolution of belowground communities and their feedback mechanisms on SOC dynamics helps embed the ecology of soil microbiome into carbon cycling, which serves to improve biodiversity conservation and carbon management strategy under global change. Here, croplands with a SOC gradient were used to understand how belowground metabolisms and SOC decomposition were linked to the diversity, composition, and co-occurrence networks of belowground communities encompassing archaea, bacteria, fungi, protists, and invertebrates. As SOC decreased, the diversity of prokaryotes and eukaryotes also decreased, but their network complexity showed contrasting patterns: prokaryotes increased due to intensified niche overlap, while that of eukaryotes decreased possibly because of greater dispersal limitation owing to the breakdown of macroaggregates. Despite the decrease in biodiversity and SOC stocks, the belowground metabolic capacity was enhanced as indicated by increased enzyme activity and decreased enzymatic stoichiometric imbalance. This could, in turn, expedite carbon loss through respiration, particularly in the slow-cycling pool. The enhanced belowground metabolic capacity was dominantly driven by greater multitrophic network complexity and particularly negative (competitive and predator-prey) associations, which fostered the stability of the belowground metacommunity. Interestingly, soil abiotic conditions including pH, aeration, and nutrient stocks, exhibited a less significant role. Overall, this study reveals a greater need for soil C resources across multitrophic levels to maintain metabolic functionality as declining SOC results in biodiversity loss. Our researchers highlight the importance of integrating belowground biological processes into models of SOC turnover, to improve agroecosystem functioning and carbon management in face of intensifying anthropogenic land-use and climate change.

Carbon emissions and priming effects derived from crop residues and their responses to nitrogen inputs

Crop residue-derived carbon (C) emissions and priming effects (PE) in cropland soils can influence the global C cycle. However, their corresponding generality, driving factors, and responses to nitrogen (N) inputs are poorly understood. As a result, the total C emissions and net C balance also remain mysterious. To address the above knowledge gaps, a meta-analysis of 1123 observations, taken from 51 studies world-wide, has been completed. The results showed that within 360 days, emission ratios of crop residues C (ER) ranged from 0.22% to 61.80%, and crop residues generally induced positive PE (+71.76%). Comparatively, the contribution of crop residue-derived C emissions (52.82%) to total C emissions was generally higher than that of PE (12.08%), emphasizing the importance of reducing ER. The ER and PE differed among crop types, and both were low in the case of rice, which was attributed to its saturated water conditions. The ER and PE also varied with soil properties, as PE decreased with increasing C addition ratio in soils where soil organic carbon (SOC) was less than 10‰; in contrast, the opposite phenomenon was observed in soils with SOC exceeding 10‰. Moreover, N inputs increased ER and PE by 8.31% and 3.78%, respectively, which was predominantly attributed to (NH4 )2 SO4 . The increased PE was verified to be dominated by microbial stoichiometric decomposition. In summary, after incorporating crop residues, the total C emissions and relative net C balance in the cropland soils ranged from 0.03 to 23.47 mg C g-1 soil and 0.21 to 0.97 mg C g-1 residue-C g-1 soil, respectively, suggesting a significant impact on C cycle. These results clarify the value of incorporating crop residues into croplands to regulate global SOC dynamics and help to establish while managing site-specific crop return systems that facilitate C sequestration.

Changes in bacterial communities during rice cultivation remove phenolic constraints on peatland carbon preservation

Northern peatlands contain ~30% of terrestrial carbon (C) stores, but in recent decades, 14% to 20% of the stored C has been lost because of conversion of the peatland to cropland. Microorganisms are widely acknowledged as primary decomposers, but the keystone taxa within the bacterial community regulating C loss from cultivated peatlands remain largely unknown. In this study, we investigated the bacterial taxa driving peat C mineralization during rice cultivation. Cultivation significantly decreased concentrations of soil organic C, dissolved organic C (DOC), carbohydrates, and phenolics but increased C mineralization rate (CMR). Consistent with the classic theory that phenolic inhibition creates a "latch" that reduces peat C decomposition, phenolics were highly negatively correlated with CMR in cultivated peatlands, indicating that elimination of inhibitory phenolics can accelerate soil C mineralization. Bacterial communities were significantly different following peatland cultivation, and co-occurrence diagnosis analysis revealed substantial changes in network clusters of closely connected nodes (modules) and bacterial keystone taxa. Specifically, in cultivated peatlands, bacterial modules were significantly negatively correlated with phenolics, carbohydrates, and DOC. While keystone taxa Xanthomonadales, Arthrobacter, and Bacteroidetes_vadinHA17 can regulate bacterial modules and promote carbon mineralization. Those observations indicated that changes in bacterial modules can promote phenolic decomposition and eliminate phenolic inhibition of labile C decomposition, thus accelerating soil organic C loss during rice cultivation. Overall, the study provides deeper insights into microbe-driven peat C loss during rice cultivation and highlights the crucial role of keystone bacterial taxa in the removal of phenolic constraints on peat C preservation.

Synergistic effect triggered by Fe2O3 and oxygen-induced hydroxyl radical enhances formation of amino-phenolic humic-like substance

Metal oxides play a promising role in the transformation of polyphenols and amino acids involved in naturally occurring humification. The objective of this study was to explore the synergistic interactions between Fe2O3 and O2 in the formation of humic substances under a controlled O2 atmosphere (0%, 21% and 40% O2 levels). The results indicate that an O2 level of 21% with Fe2O3 was optimal for humic acid (HA) production. Hydroxyl radicals (∙OH) formed and promoted the formation of HA in the presence of O2, and O2 improved the enhancing capacity of Fe2O3 by oxidizing Fe(II) to Fe(III). Moreover, the combination of these processes resulted in a synergistic improvement in humification. The evolution of functional groups in HA suggested that O2 promoted the formation of oxygen-containing groups such as lipids, and Fe2O3 was conducive to the formation of dark-coloured polymers during the darkening process of humification. Furthermore, the O2 level of 40% inhibited the formation of HA by reducing the transformation from Fe(III) to Fe(II). The XRD results showed few changes in the composition of Fe2O3 before and after humification, which indicated that Fe2O3 was a catalyst and an oxidant. The heterospectral UV-Vis/FTIR results suggested that ∙OH attacked phenolic rings to form the aromatic ring skeleton of HA and benefit the ring-opening copolymerization of humic precursors. In addition, structural equation modelling demonstrated that dissolved Fe was the key parameter affecting the HA yield. These findings provide new insights into the synergism of O2-mediated ∙OH production associated with metal oxide-facilitated humification.

Deciphering the dual role of bacterial communities in stabilizing rhizosphere priming effect under intra-annual change of growing seasons

The rhizosphere priming effect (RPE) is a widely observed phenomenon affecting carbon (C) turnover in plant-soil systems. While multiple cropping and seasonal changes can have significant impacts on RPE, the mechanisms driving these processes are complex and not yet fully understood. Here, we planted maize in paddy soil during two growing seasons having substantial temperature differences [May-August (warm season, 26.6 °C) and September-November (cool season, 23.1 °C)] within the same calendar year in southern China to examine how seasonal changes affect RPEs and soil C. We identified sources of C emissions by quantifying the natural abundance of 13C and determined microbial metabolic limitations or efficiency and functional genes related to C cycling using an enzyme-based biogeochemical equilibrium model and high-throughput quantitative PCR-based chip technology, respectively. Results showed that microbial metabolism was mainly limited by phosphorus in the warm season, but by C in the cool season, resulting in positive RPEs in both growing seasons, but no significant differences (9.02 vs. 6.27 mg C kg-1 soil day-1). The RPE intensity remained stable as temperature increased (warm season compared to a cool season), which can be largely explained by the simultaneous increase in the abundance of functional genes related to both C degradation and fixation. Our study highlights the simultaneous response and adaptation of microbial communities to seasonal changes and hence contributes to an understanding and prediction of microbially mediated soil C turnover under multiple cropping systems.

Fertilization Weakens the Ecological Succession of Dissolved Organic Matter in Paddy Rice Rhizosphere Soil at the Molecular Level

Dissolved organic matter (DOM) is involved in numerous biogeochemical processes, and understanding the ecological succession of DOM is crucial for predicting its response to farming (e.g., fertilization) practices. Although plentiful studies have examined how fertilization practice affects the content of soil DOM, it remains unknown how long-term fertilization drives the succession of soil DOM over temporal scales. Here, we investigated the succession of DOM in paddy rice rhizosphere soils subjected to different long-term fertilization treatments (CK: no fertilization; NPK: inorganic fertilization; OM: organic fertilization) along with plant growth. Our results demonstrated that long-term fertilization significantly promoted the molecular chemodiversity of DOM, but it weakened the correlation between DOM composition and plant development. Time-decay analysis indicated that the DOM composition had a shorter halving time under CK treatment (94.7 days), compared to NPK (337.4 days) and OM (223.8 days) treatments, reflecting a lower molecular turnover rate of DOM under fertilization. Moreover, plant development significantly affected the assembly process of DOM only under CK, not under NPK and OM treatments. Taken together, our results demonstrated that long-term fertilization, especially inorganic fertilization, greatly weakens the ecological succession of DOM in the plant rhizosphere, which has a profound implication for understanding the complex plant-DOM interactions.

Nonmicrobial mechanisms dominate the release of CO2 and the decomposition of organic matter during the short-term redox process in paddy soil slurry

Both biotic and abiotic mechanisms play a role in soil CO2 emission processes. However, abiotically mediated CO2 emission and the role of reactive oxygen species are still poorly understood in paddy soil. This study revealed that •OH promoted CO2 emission in paddy soil slurries during short-term oxidation (4 h). •OH generation was highly hinged on active Fe(II) content, and the •OH contribution to CO2 efflux was 10%-33% in topsoil and 40%-77% in deep-soil slurries. Net CO2 efflux was higher in topsoil slurries, which contained more dissolved organic carbon (DOC). CO2 efflux correlated well with DOC contents, suggesting the critical role of DOC. Microbial mechanisms contributed 9%-45% to CO2 production, as estimated by γ-ray sterilization experiments in the short-term reoxidation process. Solid-aqueous separation experiments showed a significant reduction in net CO2 efflux across all soil slurries after the removal of the original aqueous phase, indicating that the water phase was the main source of CO2 emission (>50%). Besides, C emission was greatly affected by pH fluctuation in acidic soil but not in neutral/alkaline soils. Fourier transform ion cyclotron resonance mass spectrometry and excitation-emission matrix results indicated that recalcitrant and macromolecular dissolved organic matter (DOM) components were more easily removed or attacked by •OH. The decrease in DOM content during the short-term reoxidation was the combined result of •OH oxidation, co-precipitation, and soil organic matter release. This study emphasizes the significance of the generally overlooked nonmicrobial mechanisms in promoting CO2 emission in the global C cycle, and the critical influence of the aqueous phase on C loss in paddy environments.

Difference Analysis of the Composition of Iron (Hydr)Oxides and Dissolved Organic Matter in Pit Mud of Different Pit Ages in Luzhou Laojiao and Its Implications for the Ripening Process of Pit Mud

Long-term production practice proves that good liquor comes out of the old cellar, and the aged pit mud is very important to the quality of Luzhou-flavor liquor. X-ray diffraction, Fourier transform ion cyclotron resonance mass spectrometry, and infrared spectroscopy were used to investigate the composition characteristics of iron-bearing minerals and dissolved organic matter (DOM) in 2-year, 40-year, and 100-year pit mud and yellow soil (raw materials for making pit mud) of Luzhou Laojiao distillery. The results showed that the contents of total iron and crystalline iron minerals decreased significantly, while the ratio of Fe(II)/Fe(III) and the content of amorphous iron (hydr)oxides increased significantly with increasing cellar age. DOM richness, unsaturation, and aromaticity, as well as lignin/phenolics, polyphenols, and polycyclic aromatics ratios, were enhanced in pit mud. The results of the principal component analysis indicate that changes in the morphology and content of iron-bearing minerals in pit mud were significantly correlated with the changes in DOM molecular components, which is mainly attributed to the different affinities of amorphous iron (hydr)oxides and crystalline iron minerals for the DOM components. The study is important for understanding the evolution pattern of iron-bearing minerals and DOM and their interactions during the aging of pit mud and provides a new way to further understand the influence of aged pit mud on Luzhou-flavor liquor production.

Iron-Nitrogen Amendment Reduced Perfluoroalkyl Acids' Phyto-Uptake in the Wheat-Soil Ecosystem: Contributions of Dissolved Organic Matters in Soil Solution and Root Extracellular Polymeric Substances

Understanding the mechanisms underlying perfluoroalkyl acids (PFAAs) translocation, distribution, and accumulation in wheat-soil ecosystems is essential for agricultural soil pollution control and crop ecological risk assessment. This study systematically investigated the translocation of 13 PFAAs under different iron and nitrogen fertilization conditions in a wheat-soil ecosystem. Short-chain PFAAs including PFBA, PFPeA, PFHxA, and PFBS mostly accumulated in soil solution (10.43-55.33%) and soluble extracellular polymeric substances (S-EPS) (11.39-14.77%) by the adsorption to amino- (-NH2) and hydroxyl (-OH) groups in dissolved organic matter (DOM). Other PFAAs with longer carbon chain lengths were mostly distributed on the soil particle surface by hydrophobic actions (74.63-94.24%). Iron-nitrogen amendments triggered (p < 0.05) soil iron-nitrogen cycling, rhizospheric reactive oxygen species fluctuations, and the concentration increases of -NH2 and -OH in the DOM structure. Thus, the accumulation capacity of PFAAs in soil solution and root EPS was increased. In sum, PFAAs' translocation from soil particles to wheat root was synergistically reduced by iron and nitrogen fertilization through increased adsorption of soil particles (p < 0.05) and the retention of soil solution and root EPSs. This study highlights the potential of iron-nitrogen amendments in decreasing the crop ecological risks to PFAAs' pollution.

Greenhouse gas emission during swine manure aerobic composting: Insight from the dissolved organic matter associated microbial community succession

Greenhouse gas emissions during aerobic composting is unavoidable, but good practices can minimize emission. Therefore, to explore the key factors influencing the release of greenhouse gas emissions during composting, the inaction of organic matter conversion, greenhouse gas emissions and bacterial community structure during co-composting with different ratio (pig manure and corn straw) over a 6-week period was studied. The excitation-emission matrix fluorescence spectroscopy with the parallel factor was used to identify that dissolved organic matter associated microbial community succession mainly influenced greenhouse gas emissions. Protein-like fractions of dissolved organic matter were more likely to decompose and promote CH₄ and CO₂ emissions, while the humic-like fractions of dissolved organic matter positively affected N₂O emissions. The largest of greenhouse gas emissions was appeared in MR2 with 12.7 kg CO₂-eq, and the MR3 and MR4 reduced greenhouse gas emissions by 26.8 % and 11.4 %, respectively.

Climate Warming Does Not Override Eutrophication, but Facilitates Nutrient Release from Sediment and Motivates Eutrophic Process

The climate is changing. The average temperature in Wuhan, China, is forecast to increase by at least 4.5 °C over the next century. Shallow lakes are important components of the biosphere, but they are sensitive to climate change and nutrient pollution. We hypothesized that nutrient concentration is the key determinant of nutrient fluxes at the water-sediment interface, and that increased temperature increases nutrient movement to the water column because warming stimulates shifts in microbial composition and function. Here, twenty-four mesocosms, mimicking shallow lake ecosystems, were used to study the effects of warming by 4.5 °C above ambient temperature at two levels of nutrients relevant to current degrees of lake eutrophication levels. This study lasted for 7 months (April–October) under conditions of near-natural light. Intact sediments from two different trophic lakes (hypertrophic and mesotrophic) were used, separately. Environmental factors and bacterial community compositions of overlying water and sediment were measured at monthly intervals (including nutrient fluxes, chlorophyll a [chl a], water conductivity, pH, sediment characteristics, and sediment-water et al.). In low nutrient treatment, warming significantly increased chl a in the overlying waters and bottom water conductivity, it also drives a shift in microbial functional composition towards more conducive sediment carbon and nitrogen emissions. In addition, summer warming significantly accelerates the release of inorganic nutrients from the sediment, to which microorganisms make an important contribution. In high nutrient treatment, by contrast, the chl a was significantly decreased by warming, and the nutrient fluxes of sediment were significantly enhanced, warming had considerably smaller effects on benthic nutrient fluxes. Our results suggest that the process of eutrophication could be significantly accelerated in current projections of global warming, especially in shallow unstratified clear-water lakes dominated by macrophytes.

Application of earthworm and silicon can alleviate antibiotic resistance in soil-Chinese cabbage system with ARGs contamination

Organic fertilization is a major contributor to the spread of antibiotic resistance genes (ARGs) in the agroecosystem, which substantially increases the risk of ARGs acquisition and their transmission into human food chains. Earthworms are among the most vital soil faunas involved in the link between belowground and aboveground, and silicon is beneficial for soil health and plant stress resistance. This study aims to explore the effect of different amendment strategies (earthworm and/or silicon) and the related influencing factors on the alleviation of ARGs using high-throughput qPCR. The results showed that the application of earthworms and silicon fertilizers reduced the absolute abundance of ARGs in the rhizosphere soils, either singly or in combination. According to the structural equation model and random forest analysis, mobile genetic elements are the major factors enhancing ARGs transfers and the treatment affects ARGs in direct or indirect ways. Our results highlight the role of "rhizosphere effect" in alleviating antibiotic resistance and suggest that silicon fertilizers, together with the earthworms, can be considered as a sustainable and natural solution to mitigate high-risk ARGs spread in the soil-plant systems. Our findings provide guidance in formulating strategies for halting the spread of ARGs in the agroecosystem.

Impacts of iron amendments and per-fluoroalkyl substances' bio-availability to the soil microbiome in wheat ecosystem

Per-fluoroalkyl substances (PFASs) have become ubiquitous in farmland ecosystems and pose risks to agricultural safety, and iron is often applied to farmland soils to reduce the availability of pollutants. However, the effects of iron amendment on the availability of PFASs in the soil and on the soil microbiome are not well understood. Here, we investigated the responses of wheat soil containing PFASs to iron addition using a 21-day experiment. Our results showed that iron amendment enhanced PFAS availability (p < 0.05) and stimulated superoxide dismutase (SOD) activity in the wheat soil (p < 0.05), but iron amendment decreased the activities of soil catalase (CAT) and peroxidase (POD) (p < 0.05). Soil bacterial community was more structurally stable than fungal community in response to iron addition, while species' pools were more stable in fungi than in bacteria (p < 0.05). Finally, PFPeA's availability in the wheat soil was the most important abiotic factors driving community succession of iron-cycling bacteria (p < 0.05). These results highlighted the potential interactions among PFASs' availability and microbial iron cycling in wheat farmland soil ecosystems and provided guidance in farmland environmental conservation and management.