Atmospheric nitrous oxide (N2O) is one of the principal greenhouse gases and the largest ozone-depleting substance in the stratosphere. The growth of the atmospheric N2O burden has been mainly attributed to emissions from agricultural fields. However, N2O emissions measured by using conventional static chambers (CSCs) usually suffer from serious artifacts that influence the estimations of the global N2O budget. In this study, N2O fluxes from an agricultural field in the North China Plain (NCP) were comparably measured by using CSCs, CSCs with dehumidification, and open-top dynamic chambers (OTDCs) to reveal the artifact of humidity accumulation inside CSCs on N2O emissions. The air relative humidity and topsoil moisture inside the CSCs were found to be significantly higher than those inside the OTDCs and over/in the field, leading to the CSCs' overestimation of N2O emissions by factors of 2.3-3.6. The overestimation of N2O emissions by CSCs was further verified by soil simulation experiments in a flow tube by flushing the soil with varying air humidity. The results of this study underscore that future efforts should prioritize validating the estimates of N2O emissions from key sources using minimally intrusive methods like dynamic chambers or micrometeorological methods.

Chenopodioideae plants are dominant components of desert ecosystems in arid regions of China and Central Asia and play key roles in maintaining ecosystem stability, while also providing valuable systems for understanding evolutionary and environmental adaptations of desert vegetation. However, at the family level, stoichiometric patterns across functional groups and plant organs in Chenopodioideae species remain poorly understood. We investigated 68 desert sites along a > 2000 km desert transect in northwestern China and collected leaf and stem samples from 39 Chenopodioideae species. After data preprocessing and standardization, 167 independent leaf units and 161 independent stem units were retained for subsequent analyses. We examined variation patterns and environmental drivers of nitrogen (N), phosphorus (P), and potassium (K) across functional groups (C3 vs. C4 plants; trees, shrubs, and herbs) and organs (stems and leaves) at the community level. Compared with global and national datasets, Chenopodioideae plants exhibited lower N concentrations (8.846 mg g− 1 in stems and 15.768 mg g− 1 in leaves) but higher P (1.235 mg g− 1 and 1.497 mg g− 1) and K concentrations (23.758 mg g− 1 and 27.656 mg g− 1), suggesting potential nitrogen limitation. Significant differences in nutrient concentrations were observed among most functional groups and organs. Based on community-weighted means, leaves exhibited consistently lower P-K scaling exponents than stems across functional groups, suggesting enhanced K-related stress resistance. Stem and leaf N, P, N: P, and P: K exhibited homeostatic or strictly homeostatic patterns, supporting the “Stability of Limiting Elements Hypothesis”. Nutrient traits showed divergent responses along latitude, longitude, and aridity gradients, reflecting diverse adaptive strategies. Environmental drivers varied among traits and organs. Soil, climatic, and geographical factors jointly regulated nutrient concentrations and ratios through interacting pathways, with soil factors generally exerting stronger relative influences. Overall, our findings reveal differentiated yet partially convergent stoichiometric strategies among functional groups and organs, highlighting adaptive nutrient regulation mechanisms in arid desert ecosystems.

With intensified dam construction in recent decades, river connectivity has been disrupted, reshaping elemental cycling and aggravating C: N: P imbalances. Here, we investigate how long-term cascade damming regulates particulate C: N: P stoichiometry along the upper Yangtze River in China. We show that the contribution of autochthonous particulate organic carbon (A-POC) gradually increases with reservoir age and hydraulic retention time, particularly near dams. Cascade impoundments stimulate reservoir-induced phytoplankton production that increasingly outweighs terrestrial anthropogenic inputs, leading to a 39% decline in particulate C: N ratios from the upper reach of the Jinsha River to the Three Gorges Reservoir, approaching Redfield ratios. With continued operation, particulate C: N in reservoirs converges toward Redfield thresholds within similar to 30 years of post-impoundment, yet may fall below 6.625 after prolonged impoundment, altering the regulation of particulate C: P and N: P from particulate phosphorus (PP)-dominated control to joint particulate organic matter-PP control. These results reveal the dual role of cascade reservoirs as both disruptors and gradual restorers of elemental balance, with long-term ecological succession fostering stoichiometric convergence. Targeted regulation of phytoplankton biomass and watershed PP inputs is therefore essential for mitigating stoichiometric imbalance and guiding adaptive management in large dammed river-reservoir systems.

Carbonyl compounds are significant in atmospheric chemistry and human health, yet their sources, especially in rural areas, remain incompletely characterized. Long-term measurements (June 2020-July 2021) at a rural site in the North China Plain (NCP) identified formaldehyde, acetaldehyde, and acetone as the dominant carbonyls, collectively accounting for 71 % of the total. Concentrations exhibited distinct seasonal patterns, with the highest levels observed for all three compounds during autumn. Analysis of C1/C2 ratios and correlation analysis indicated anthropogenic emissions as the primary source overall. Notably, during autumn, strong mutual correlations among formaldehyde, acetaldehyde, and acetone were observed, contrasting with weaker correlations to CO and O3. Supplementary experiments confirmed that mechanical corn stover crushing releases substantial amounts of carbonyls. These convergent findings demonstrate that large-scale seasonal agricultural activities, particularly corn stover crushing and agricultural machinery during harvest periods, constitute a major and previously underappreciated source of carbonyl emissions in the NCP region, necessitating greater attention in emission inventories and mitigation strategies. Furthermore, integrated lifetime cancer risk (ILTCR) and hazard quotient (HQ) assessments indicated that formaldehyde concentrations pose a potential lifetime carcinogenic risk to the local population.

The intensification of freshwater aquaculture has raised growing concerns regarding heavy metal contamination and related human health risks. This study compared three types of freshwater aquaculture systems: the traditional rice-fish co-culture (TRF), the modern intensive rice-fish co-culture (MRF), and the pond culture (PC), using Qingtian paddy field carp (Cyprinus carpio var. qingtianensis) as the indicator species. Concentrations of arsenic (As), cadmium, lead (Pb), chromium (Cr), and mercury (Hg) were measured in both fish muscle and sediment samples. The comprehensive pollution index (Pi) for fish muscle exceeded the safety threshold in all systems. The estimated daily intake (EDI) for Cr and Hg in the examined fish muscle samples exceeded detection limits across all systems. The target hazard quotient (THQ) for each metal was below 1, however, the total THQ (TTHQ) for MRF system reached 1.06, with Cr contributing approximately 60 %. Despite lower productivity, the TRF system demonstrated the lowest health risk and ecological impact, supporting its role as a model for sustainable aquaculture. These results emphasize the importance of strengthening feed management and quality control in intensive systems to minimize the risks of heavy metal exposure.

The application of nitrogen fertilizers in agricultural fields can lead to the release of nitrogen-containing gases (NCGs), such as NOx, NH3 and N2O, which can significantly impact regional atmospheric environment and contribute to global climate change. However, there remain considerable research gaps in the accurate measurement of NCGs emissions from agricultural fields, hindering the development of effective emission reduction strategies. We improved an open-top dynamic chambers (OTDCs) system and evaluated the performance by comparing the measured and given fluxes of the NCGs. The results showed that the measured fluxes of NO, N2O and NH3 were 1 %, 2 % and 7 % lower than the given fluxes, respectively. For the determination of NH3 concentration, we employed a stripping coil-ion chromatograph (SC-IC) analytical technique, which demonstrated an absorption efficiency for atmospheric NH3 exceeding 96.1 % across sampling durations of 6 to 60 min. In the summer maize season, we utilized the OTDCs system to measure the exchange fluxes of NO, NH3, and N2O from the soil in the North China Plain. Substantial emissions of NO, NH3 and N2O were recorded following fertilization, with peaks of 107, 309, 1239 ng N/(m2·s), respectively. Notably, significant NCGs emissions were observed following sustained heavy rainfall one month after fertilization, particularly with NH3 peak being 4.5 times higher than that observed immediately after fertilization. Our results demonstrate that the OTDCs system accurately reflects the emission characteristics of soil NCGs and meets the requirements for long-term and continuous flux observation.

Peroxyacetyl nitrate (PAN) is an important photochemical pollutant in the troposphere, whereas long-term measurements are scarce in rural areas in North China Plain (NCP), resulting in unclear seasonal variations and sources of PAN in rural NCP. In this study, we conducted a 1-year observation of PAN during 2021-2022 at the rural NCP site. The average concentrations of PAN were 1.10, 0.75, 0.65, and 0.88 ppbv in spring, summer, autumn, and winter, respectively, with a 1-year average of 0.81 ± 0.60 ppbv. Calculations indicate that the loss of PAN through thermal decomposition in summer accounts for 43.2% of the total formed PAN, which is an important reason for the low concentration of PAN in summer. We speculate that since the correlation between PAN and O3 in winter is significantly lower than that in other seasons, the observed regional transport of PAN cannot be ignored in winter. Through budget analysis, regional transport accounted for 12.8% and 55.9% of the observed PAN on the spring and winter pollution days, respectively, which showed that regional transport played key roles during the photochemical pollution of the rural NCP in winter. The potential source contribution function revealed that the transported PAN mainly comes from southern Hebei in spring. In winter, the transported PAN was mainly from Langfang, Hengshui, and southern Beijing. Our findings may aid in understanding PAN variations in different seasons in rural areas and highlight the impact of regional transport on the PAN budget.

Gaseous nitrous acid (HONO) is a critical contributor to daytime hydroxyl radical in the troposphere. Livestock farming has been recognized as an overlooked HONO source, but the lack of detailed flux measurements from livestock and poultry wastes would cause uncertainties in modeling its environmental impacts. Here, based on field flux measurements and laboratory experiments, we observed substantial HONO emissions from the composting of swine feces and chicken manure in the warm season, which might be mainly attributed to nitrification process in livestock and poultry wastes. The HONO emission from chicken manure was found to be much higher than that from swine feces, and the higher NH3 emission but lower N2O and NO emissions from chicken manure were also observed. Considering that the interaction among these nitrogen species during nitrification process, the obviously lower HONO emission from swine feces was likely to be explained by the lack of the total ammonia nitrogen and H+ donors in swine feces. Temperature is also a key factor that influences the HONO emission from livestock wastes. In addition, the total HONO emission from swine feces in China was estimated to be approximately 107.7 Gg-N/yr according to the national swine amounts, which is comparable to the national soil HONO emissions, underscoring its non-negligible contribution to regional air quality. Therefore, effective emission control of HONO from livestock and poultry wastes should be carried out to further improve air quality in China.

HONO acts as a major OH source, playing a vital role in secondary pollutant formation to deteriorate regional air quality. Strong unknown sources of daytime HONO have been widely reported, which significantly limit our understanding of radical cycling and atmospheric oxidation capacity. Here, we identify a potential daytime HONO and OH source originating from photoexcited phenyl organic nitrates formed during the photoreaction of aromatics and NOx. Significant HONO (1.56-4.52 ppb) and OH production is observed during the photoreaction of different kinds of aromatics with NOx (18.1-242.3 ppb). We propose an additional mechanism involving photoexcited phenyl organic nitrates (RONO2) reacting with water vapor to account for the higher levels of measured HONO and OH than the model prediction. The proposed HONO formation mechanism was evidenced directly by photolysis experiments using typical RONO2 under UV irradiation conditions, during which HONO formation was enhanced by relative humidity. The 0-D box model incorporated in this mechanism accurately reproduced the evolution of HONO and aromatic. The proposed mechanism contributes 5.9-36.6% of HONO formation as the NOx concentration increased in the photoreaction of aromatics and NOx. Our study implies that photoexcited phenyl organic nitrates are an important source of atmospheric HONO and OH that contributes significantly to atmospheric oxidation capacity.

L-tryptophan is an essential amino acid that is widely used in food, medicine and feed sectors. L-tryptophan can be produced through fermentation, and the main producing strains are engineered Escherichia coli and Corynebacterium glutamicum, which are constructed by rational design methods based on metabolic engineering and synthetic biology. However, due to the long metabolic pathway, complex and unclear regulatory mechanism for L-tryptophan production in microbial cells, the production efficiency and robustness of L-tryptophan producing strains are still low. In this connection, irrational design methods such as laboratory adaptive evolution, are often applied to improve the performance of L-tryptophan producing strains. This review summarizes the recent progress on biosynthesis metabolism of L-tryptophan and its regulation, the construction and optimization of L-tryptophan producing strains, and fermentative production of L-tryptophan, and prospects future development perspective. This review may facilitate research and development for fermentative production of L-tryptophan.

Fertilized agricultural soil is a significant source of gaseous nitrogen compounds (GNCs), including N2O, NO, HONO, and NH3. The North China Plain (NCP) is the "hot region" for the release of these GNCs due to intensive fertilization practices. However, existing research has primarily focused on N2O emissions from fertilized farmland in the NCP, lacking comprehensive observational studies on other GNCs. Therefore, a continuous cumulative sampling technique (open-top dynamic chamber system) was utilized in this study to simultaneously measure the exchange fluxes of N2O, NO, HONO, and NH3 over summer maize-winter wheat rotation fields in the NCP. Results showed that GNC emissions from the soil displayed distinct diurnal variations, with higher emissions during the day attributed to elevated soil temperature. However, N2O emissions remained consistent between day and night, potentially influenced not only by soil temperature but also by soil humidity. Annual cumulative emissions and emission factors (EFs) for four GNCs were determined, indicating that N2O, NO, and NH3 emissions during the maize season were 1.38-2.37 times higher than those during the wheat season, with 98 % of HONO emissions occurring in the maize season. Additionally, the study first presented the annual HONO EFs of 0.36 +/- 0.03 % in fertilized farmland. Furthermore, a comparison revealed that the fluxes of N2O, NO, NH3, and HONO using the conventional single-point sampling method were 26.4 %, 13.9 %, and 8.10 % lower, and 7.86 % higher compared to the continuous cumulative sampling method recommended in this study. In general, this study provided precise measurements of GNC emissions from farmland, offering essential foundational data for modeling parameters and contributing to the formulation of regional air pollution prevention and control policies.

Nitrous acid (HONO) is a crucial precursor of tropospheric hydroxyl radicals, but its sources are not fully understood. Soil is recognized as an important HONO source, but the lack of measurements of soil–atmosphere HONO exchange flux (FHONO) has led to uncertainties in modeling its atmospheric impacts and understanding the reactive nitrogen budget. Herein, we conduct FHONO measurements over agricultural fields under fertilized (FHONO-NP, normal fertilization and irrigation) and non-fertilized (FHONO-CK, normal irrigation but no fertilization) treatments. Our results show that nitrogen fertilizer use causes a remarkable increase in FHONO-NP. FHONO-NP exhibits distinct diurnal variations, with an average noontime peak of 152 ng N m−2 s−1. The average FHONO-NP within 3 weeks after fertilization is 97.7±8.6 ng N m−2 s−1, around 2 orders of magnitude higher than before fertilization, revealing the remarkable promotion effect of nitrogen fertilizer on HONO emissions. We also discuss other factors influencing soil HONO emissions, such as meteorological parameters and soil properties/nutrients. Additionally, we estimate the HONO emission factor of 0.68±0.07 % relative to the applied nitrogen during the whole growing season of summer maize. Accordingly, the fertilizer-induced soil HONO emission is estimated to be 22.3 and 60.8 Gg N yr−1 in the North China Plain (NCP) and mainland China, respectively, representing a significant reactive nitrogen source. Furthermore, our observations reveal that soil emissions sustain a high level of daytime HONO, enhancing the atmospheric oxidizing capacity and aggravating O3 pollution in the NCP. Our results indicate that to mitigate regional air pollution effectively, future policies should consider reactive nitrogen emissions from agricultural soils.

Nitrous acid (HONO) is a crucial precursor of tropospheric hydroxyl radicals but its 20 sources are not fully understood. Soil is recognized as an important HONO source, but the lack of measurements of soil-atmosphere HONO exchange flux (F HONO ) has led to uncertainties in modeling its atmospheric impacts and understanding the reactive nitrogen budget. To address this, we conduct long-period F HONO measurements over agricultural fields under fertilized (F HONO-NP ) and non-fertilized (F HONO-CK ) treatments. 25 Our results show that nitrogen fertilizer use causes a remarkable increase in F HONO-NP and it exhibits distinct diurnal variations, with an average noontime peak of 152 ng N m -2 s -1 . The average F HONO-NP within three weeks after fertilization is 97.7 ± 8.6 ng N m -2 s -1 , around two orders of magnitude higher than before fertilization, revealing the remarkable promotion effect of nitrogen fertilizer on HONO emissions. 30 We also discuss other factors that influence soil HONO emissions, such as meteorological parameters and soil properties/nutrients. Additionally, we estimate the HONO emission factor of 0.68 ± 0.07% relative to the applied nitrogen during the whole growing season of summer maize. Accordingly, the fertilizer-induced soil HONO emission is estimated to be 0.06 and 0.16 Tg N yr -1 in the North China Plain (NCP) and 35 China, respectively, representing a significant reactive nitrogen source. Furthermore, our observations reveal that soil emissions sustain a high level of daytime HONO, enhancing the atmospheric oxidizing capacity and aggravating O 3 pollution in the NCP. Our results indicate that in order to effectively mitigate regional air pollution, future policies should consider reactive nitrogen emissions from agricultural soils.

Prolonged drought due to global warming can have significant effects on tree growth and sustainability by changing physiological traits. Agroforestry is considered climate-smart and can help buffer the effects of extreme climates. However, it remains unclear as to how trees in agroforestry physiologically adapt to prolonged drought in semiarid regions. Here, we report results from a three-year rainfall exclusion experiment (an extreme natural drought occurred during the experiment) designed to understand the physiological mechanism of young apple trees responding to different degrees of prolonged drought (moderate drought by reducing rainfall by 15% and severe drought by reducing rainfall by 25%) in an alley agroforestry system constituting of apple trees and oil crops. We found that the measured physiological traits for young apple tree under agroforestry were not clearly different from those under monoculture, although soil water content in the top 80 cm was reduced by 9.3%. Under moderate drought conditions, the apple trees in agroforestry implemented a conservative water-use strategy. Stomatal conductance, photosynthesis, and leaf transpiration were reduced by 15.5%, 3.8%, and 12.6%, respectively, whereas pre-dawn (psi pd) and midday (psi md) leaf water potential stabilized, indicating a clear isohydric behavior. Under severe drought conditions, however, the apple trees still maintained normal stomatal opening to significantly (p<0.01) increase photosynthesis (9.8%) and leaf transpiration (12%) at the expense of reducing psi pd (58.1%) and psi md (25.4%), showing anisohydric behavior which can place apple trees at risk. Reduction of aboveground biomass and greater numbers of fine roots in deeper soils to explore deep-layer soil water could explain such risky behavior by apple trees suffering severe drought. The findings here provide new insights into the mechanism through which the coordination between canopy water consumption and above-ground/belowground biomass redistribution of trees underpin the physiological adaptation of trees to different degrees of prolonged drought in semiarid regions.

Recently, deteriorating ozone (O3) pollution in China brought the precise diagnosis of O3 sensitive chemistry to the forefront. As a dominant precursor of OH radicals, atmospheric nitrous acid (HONO) plays an important role in O3 production. However, its measurement unavailability in many regions especially for second- and third-tier cities may lead to the misjudgment of the O3 sensitivity regime derived from observation-based models. Here, we systematically assess the potential impact of HONO on diagnosing the sensitivity of O3 production using a 0-dimension box model based on a comprehensive summer urban field campaign. The results indicated that the default mode (only the NO + OH reaction is included) in the model could underestimate ∼87% of observed HONO levels, leading to an obvious decrease (∼19%) of net O3 production in the morning, which was in line with the previous studies. The unconstrained HONO in the model was found to significantly push O3 production toward the VOC-sensitive regime. Additionally, it is unrealistic to change NO x but constrain HONO in the model due to the dependence of HONO formation on NO x . Assuming that HONO varied proportionally with NO x , a stronger NO x -sensitive condition could be achieved. Therefore, effective reduction of NO x should be given more attention together with VOC emission control for O3 mitigation.

Atmospheric HONO acts as a major source for OH radicals in polluted areas, playing an important role in formation of secondary pollutants. However, the atmospheric HONO sources remain unclear. Here we propose that the heterogeneous reaction of NO2 on aerosols during aging processes acts as the dominant source for nocturnal HONO. Based on the nocturnal variations of HONO and related species in Tai'an city of China, we firstly developed new method to estimate the localized HONO dry deposition velocity (v(HONO)). The estimated v(HONO) of 0-0.077 m/s was in a good agreement with the reported ranges. Additionally, we set up a parametrization to reflect the HONO formation from the aged air parcels based on the variation of HONO/NO2 ratio. The detailed variation of nocturnal HONO could be well reproduced by a complete budget calculation coupled with above parameterizations, with the difference between the observed and calculated HONO levels being <5 %. The results also revealed the average contribution of HONO formation from aged air parcels to atmospheric HONO could achieve to be similar to 63 % in average.

居民使用煤炭等固体燃料采暖或炊事时常排放出大量污染物,不仅会造成严重的空气污染,还严重影响居民身体健康和生命安全,受到国际社会的长期关注.本文基于居民燃煤污染物组成和煤的燃烧机理,探讨了污染物的产生及排放规律;结合居民燃煤炉灶类型,综述了居民煤炭主要燃烧技术的原理及优缺点;针对居民散煤的清洁燃烧,从居民用煤标准、清洁燃烧技术选择、清洁燃烧炉灶的科学评价几方面提出建议.

In this study, Hg isotopes, backward trajectory, and emission inventory were utilized to explore the effects of possible emission sources and photochemical pathways on fine-particle bound mercury during two single haze events in February 2017 and January 2018 at Gucheng (38.31°N, 115.25°E). Results showed that (a) the large variations of odd-mass mass-independent fractionation values in fine-particle bound mercury showed the joint contributions of different source regions during haze evolution; (b) biomass burning significantly contributed to fine-particle bound mercury during winter haze in northern China; (c) fine-particle bound mercury during haze evolution at Gucheng (an inland site in China) was impacted by marine aerosols; (d) photoreduction had a significant impact on fine-particle bound mercury during haze evolution and a relatively more intense solar radiation may be conducive to photoreduction during haze. These findings provide a theoretical basis for developing methods and strategies to control fine-particle bound mercury pollution.

Bacterial drug resistance caused by overuse and misuse of antibiotics is common, especially in clinical multispecies infections. It is of great significance to discover novel agents to treat clinical bacterial infections. Studies have demonstrated that autoinducer-2 (AI-2), a signal molecule in quorum sensing (QS), plays an important role in communication among multiple bacterial species and bacterial drug-resistance. Previously, 14 AI-2 inhibited compounds were selected through virtual screening by using the AI-2 receptor protein LuxP as a target. Here, we used Vibrio harveyi BB170 as a reporter strain for the preliminary screening of 14 inhibitors and compound Str7410 had higher AI-2 QS inhibition activity (IC50 = 0.3724 ± 0.1091 μM). Then, co-culture of Pseudomonas aeruginosa PAO1 with Staphylococcus aureus ATCC 25923 was used to evaluate the inhibitory effects of Str7410 on multispecies infection in vitro and in vivo. In vitro, Str7410 significantly inhibited the formation of mixed bacterial biofilms. Meanwhile, the combination of Str7410 with meropenem trihydrate (MEPM) significantly improved the susceptibility of mixed-species-biofilm cells to the antibiotic. In vivo, Str7410 significantly increased the survival rate of wild-type Caenorhabditis elegans N2 co-infected by P. aeruginosa PAO1 and S. aureus ATCC 25923. Real-time quantitative PCR analysis showed that Str7410 reduced virulence factor (pyocyanin and elastase) production and swarming motility of P. aeruginosa PAO1 by downregulating the expression of QS-related genes in strain PAO1 in co-culture with S. aureus ATCC 25923. Compound Str7410 is a candidate agent for treating drug-resistant multispecies infections. The work described here provides a strategy for discovering novel antibacterial drugs.