The Salmonella effectors SseF and SseG inhibit Rab1A-mediated autophagy to facilitate intracellular bacterial survival and replication.

In mammalian cells, autophagy plays crucial roles in restricting further spread of invading bacterial pathogens. Previous studies have established that the Salmonella virulence factors SseF and SseG are required for intracellular bacterial survival and replication. However, the underlying mechanism by which these two effectors facilitate bacterial infection remains elusive. Here, we report that SseF and SseG secreted by Salmonella Typhimurium (S. Typhimurium) inhibit autophagy in host cells and thereby establish a replicative niche for the bacteria in the cytosol. Mechanistically, SseF and SseG impaired autophagy initiation by directly interacting with the small GTPase Rab1A in the host cell. This interaction abolished Rab1A activation by disrupting the interaction with its guanine nucleotide exchange factor (GEF), the TRAPPIII (transport protein particle III) complex. This disruption of Rab1A signaling blocked the recruitment and activation of Unc-51-like autophagy-activating kinase 1 (ULK1) and decreased phosphatidylinositol 3-phosphate biogenesis, which ultimately impeded autophagosome formation. Furthermore, SseF- or SseG-deficient bacterial strains exhibited reduced survival and growth in both mammalian cell lines and mouse infection models, and Rab1A depletion could rescue these defects. These results reveal that virulence factor-dependent inactivation of the small GTPase Rab1A represents a previously unrecognized strategy of S Typhimurium to evade autophagy and the host defense system.

Aestuariimicrobium soli sp. nov., isolated from farmland soil, and emended description of the genus Aestuariimicrobium.

A Gram-reaction-positive, catalase-positive, non-spore-forming and short rod- or oval-shaped bacterial strain, designated D6T, was isolated from farmland soil in Xuancheng, Anhui Province, China. Growth occurred at 4-37 °C (optimum, 30 °C), at pH 6.5-8.5 (optimum, 7.0) and with 0-7 % (w/v) NaCl (optimum, 0.5 % NaCl). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain D6T was most closely related to Aestuariimicrobium kwangyangense DSM 21549T (98.47 %), followed by Tessaracoccus rhinocerotis YIM 101269T (94.46 %). Strain D6T had a cell-wall peptidoglycan based on ll-diaminopimelic acid. MK-9(H4) was the predominant menaquinone. The major fatty acids of strain D6T were anteiso-C15 : 0, iso-C15 : 0 and summed feature 4 (iso-C17 : 1 I and/or anteiso-C17 : 1 B). The major polar lipids were a lipid, glycolipid and phospholipid. The DNA G+C content was 69.2 mol% and strain D6T showed low DNA-DNA relatedness to A. kwangyangense DSM 21549T (36.45±0.42 %). Based on these genotypic and phenotypic data, strain D6T represents a novel species in the genus Aestuariimicrobium, for which the name Aestuariimicrobium soli sp. nov. is proposed. The type strain is D6T (=KCTC 39995T=DSM 105824T). An emended description of the genus Aestuariimicrobium is presented.

Elevated ozone concentration decreases whole-plant hydraulic conductance and disturbs water use regulation in soybean plants.

Elevated tropospheric ozone (O3 ) concentration has been shown to affect many aspects of plant performance including detrimental effects on leaf photosynthesis and plant growth. However, it is not known whether such changes are accompanied by concomitant responses in plant hydraulic architecture and water relations, which would have great implications for plant growth and survival in face of unfavorable water conditions. A soybean (Glycine max (L.) Merr.) cultivar commonly used in Northeast China was exposed to non-filtered air (NF, averaged 24.0 nl l-1 ) and elevated O3 concentrations (eO3 , 40 nl l-1 supplied with NF air) in six open-top chambers for 50 days. The eO3 treatment resulted in a significant decrease in whole-plant hydraulic conductance that is mainly attributable to the reduced hydraulic conductance of the root system and the leaflets, while stem and leaf petiole hydraulic conductance showed no significant response to eO3 . Stomatal conductance of plants grown under eO3 was lower during mid-morning but significantly higher at midday, which resulted in substantially more negative daily minimum water potentials. Moreover, excised leaves from the eO3 treated plants showed significantly higher rates of water loss, suggesting a lower ability to withhold water when water supply is impeded. Our results indicate that, besides the direct detrimental effects of eO3 on photosynthetic carbon assimilation, its influences on hydraulic architecture and water relations may also negatively affect O3 -sensitive crops by deteriorating the detrimental effects of unfavorable water conditions.

Transcriptomic analysis of Pak Choi under acute ozone exposure revealed regulatory mechanism against ozone stress.

BACKGROUND: Ground-level ozone (O3) is one of the major air pollutants, which cause oxidative injury to plants. The physiological and biochemical mechanisms underlying the responses of plants to O3 stress have been well investigated. However, there are limited reports about the molecular basis of plant responses to O3. In this study, a comparative transcriptomic analysis of Pak Choi (Brassica campestris ssp. chinensis) exposed to different O3 concentrations was conducted for the first time. RESULTS: Seedlings of Pak Choi with five leaves were exposed to non-filtered air (NF, 31 ppb) or elevated O3 (E-O3, 252 ppb) for 2 days (8 h per day, from 9:00-17:00). Compared with plants in the NF, a total of 675 differentially expressed genes (DEGs) were identified in plants under E-O3, including 219 DEGs with decreased expressions and 456 DEGs with increased expressions. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that O3 stress invoked multiple cellular defense pathways to mitigate the impaired cellular integrity and metabolism, including 'glutathione metabolism', 'phenylpropanoid biosynthesis', 'sulfur metabolism', 'glucosinolate biosynthesis', 'cutin, suberine and wax biosynthesis' and others. Transcription factors potentially involved in this cellular regulation were also found, such as AP2-ERF, WRKY, JAZ, MYB etc. Based on the RNA-Seq data and previous studies, a working model was proposed integrating O3 caused reactive oxygen burst, oxidation-reduction regulation, jasmonic acid and downstream functional genes for the regulation of cellular homeostasis after acute O3 stress. CONCLUSION: The present results provide a valuable insight into the molecular responses of Pak Choi to acute O3 stress and the specific DEGs revealed in this study could be used for further functional identification of key allelic genes determining the O3 sensitivity of Pak Choi.

Evaluation of negative effect of Naphthenic acids (NAs) on physiological metabolism and polycyclic aromatic hydrocarbons adsorption of Phragmites australis.

Toxic substances in the environment disturb the adsorption of pollutants in plants but little is known about the underlying mechanisms of these processes. This study evaluated the PAH adsorption by Phragmites australis under NAs stress. Results showed that Naphthenic acids (NAs) significantly decreased the adsorption of PAHs and had higher selectivity for type and structure. P. australis root cell growth and mitosis were significantly affected by NAs, which was accompanied by serious disturbances in mitochondrial function. The physiological evaluation showed the NAs could increase Reactive Oxygen Species (ROS) accumulation by around 16-fold and cause damage to the root cell normal redox equilibrium. The levels of three key related antioxidants, PLA, CAT and POD, decreased significantly to 35-50% under NAs stress and were dependent upon NAs concentration. Furthermore, NAs could significantly change the concentration and species of root exudates of P. ausralis. Autotoxic substances, including alcohol and amines, increased by 28.63% and 23.96, respectively. Sixteen compounds were identified and assumed as potential biomarkers. Galactonic, glyceric, and octadecanoic acid had the general effect of activating PAH in soil. The global view of the metabolic pathway suggests that NAs influenced the citric acid cycle, fatty acid synthesis, amino acid metabolism and the phenylpropanoid pathway. Detection data results indicated that the energy products cause hypoxia and oxidative stress, which are the main processes under the NAs. Furthermore, verification of these processes was fulfilled through gene expression and biomarkers quantification. Our results provide novel metabolic insights into the mechanisms of PAHs adsorption by P. australis under NAs disturbance, suggesting that monitoring NAs in phytoremediation applications is necessary.

Kineococcus endophytica sp. nov., a novel endophytic actinomycete isolated from a coastal halophyte in Jiangsu, China.

A novel Gram-positive, motile, non-spore-forming coccus-shaped bacterial strain, designated KLBMP 1274(T), was isolated from a halophytic plant (Limonium sinense) collected from the coastal region of Nantong, Jiangsu Province, in east China. Phylogenetic analyses based on the 16S rRNA gene sequence showed that strain KLBMP 1274(T) belongs to the genus Kineococcus and is closely related to Kineococcus rhizosphaerae RP-B16(T) (98.72 %), Kineococcus aurantiacus IFO 15268(T) (98.71 %), Kineococcus radiotolerans SRS30216(T) (98.69 %) and Kineococcus gynurae KKD096(T) (97.33 %). The 16S rRNA gene sequence similarity to other species of the genus Kineococcus was <97 %. The cell wall contained meso-diaminopimelic acid as the diagnostic diamino acid, with arabinose and galactose as the characteristic sugars. The predominant menaquinone was MK-9(H(2)). The polar lipids were found to be diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannosides, an unknown phospholipid, an unknown glycolipid, and three unknown lipids. Major cellular fatty acids were found to be anteiso-C(15: 0) and iso-C(14: 0). The chemotaxonomic data for strain KLBMP 1274(T) were typical of the genus Kineococcus. The total DNA G+C content was 73.4 mol %. DNA-DNA relatedness and differential phenotypic data demonstrated that strain KLBMP 1274(T) was clearly distinguished from all closely related species of the genus Kineococcus. Thus, strain KLBMP 1274(T) represents a novel species of the genus Kineococcus, for which the name Kineococcus endophytica sp. nov. is proposed. The type strain is KLBMP 1274(T) (=KCTC 19886 (T) = NBRC 108674(T)).

[Changing Characteristics of Carbon-Based Greenhouse Gas Fluxes in Paddy Field in the Middle-Lower Yangtze Plain in China].

In recent years, carbon emission research has been receiving increasing attention. China has put forward the strategic goal of achieving a carbon emission peak by 2030. Hence this research is very important for the measurement of greenhouse gas emissions in China. CO2 and CH4 fluxes from a paddy field in the middle-lower Yangtze Plain in China were analyzed based on the eddy covariance technique. The CO2 flux showed an "U" curve during the observation period, with an average flux of -3.33 µmol·(m2·s)-1, which was a sink. Negative values appeared at the tillering stage, and the minimum was shown at the heading period. The CH4 flux trend was roughly opposite to the that of the CO2 flux, which first increased and then decreased. It raised rapidly during the tillering and jointing stages and then dropped rapidly from the peak to the trough during the booting stage, and only a slight increase was found in the blooming stage. The maximum flux[0.40 µmol·(m2·s)-1] appeared at the beginning of the booting stage and the end of the jointing stage, and the average flux was 0.11 µmol·(m2·s)-1. The CO2 flux was positive at night and negative during the day. It decreased from 07:00 and reached a minimum around 13:00 at -16.01 µmol·(m2·s)-1. The CH4 flux was low at night and high during the daytime. It increased at 06:00 and reached a peak around 14:00, at approximately 0.16 µmol·(m2·s)-1. An exponential correlation was found between air temperature and CH4 flux. The vapor pressure deficit showed a linear correlation with CH4 flux. The response of environmental factors on CO2 fluxes and CH4 fluxes on a diurnal scale was greater than that on a seasonal scale, and the daytime response was greater than that at night. CH4 flux decreased significantly with the increase in CO2 flux on the diurnal scale, but the correlation was not obvious on the seasonal scale. The increased CH4 flux slowed down after fertilizing.

[Relationship Between Relative Crop Yield/Woody Plant Biomass and Ground-level Ozone Pollution in China].

Currently, ground-level ozone (O3) pollution is increasingly serious in China, and highly threatens plant productivity. In this study, we summarized the relationship between relative crop yield or woody plant biomass and O3 metrics, including M7 (the mean of hourly concentrations from 09:00 to 16:00), SUM06 (sum of hourly concentrations above 60 nmol·mol-1), W126 (Sigmoidal weighted sum of the hourly concentrations during a specified period), PODY[phytotoxic O3 dose above a threshold flux of Y nmol·(m2·s)-1], and the most commonly used AOT40 (accumulated O3 concentrations over an hourly threshold of 40 nmol·mol-1), and proposed their critical level to protect plants against O3 damage. Based on the AOT40 metric, we found that the O3 risk threshold that caused a 5% decrease in yield was 5.93 µmol·mol-1·h for rice, 2.69 µmol·mol-1·h for winter wheat, 8.67 µmol·mol-1·h for maize, and 4.17 µmol·mol-1·h for soybean, indicating that maize may be more tolerant to O3 than the other three crops in China. The O3 risk threshold that led to a 5% reduction in total biomass was 12.20 µmol·mol-1·h across five poplar clones (based on experiment) and 10.87 µmol·mol-1·h across 17 woody plants (based on integrated analysis). On the other hand, some perspectives were presented concerning the establishment of O3 response relationships for important productivity-related parameters, and the improvement of accuracy in O3 regional risk assessment. It is also important to consider how to couple other important factors affecting plant O3 sensitivity (such as soil nitrogen and plant age) into the regional assessment model.

[Ozone Pollution, Nitrogen Addition, and Drought Stress Interact to Affect Non-structural Carbohydrates in the Leaves and Fine Roots of Poplar].

Ground-level ozone (O3) pollution frequently co-occurs with drought and nitrogen (N) deposition during the growing season. It is important to understand how the carbon dynamics of plants respond to O3 pollution in drier and N-enriched environments. Here we present the patterns of non-structural carbohydrates and its components (soluble sugar and starch) in the leaves and fine roots in poplar clone 546 (Populus deltoides cv. '55/56'×P. deltoides cv. 'Imperial') for one growing season at two O3 concentrations (control, charcoal-filtered air, and elevated O3, non-filtered air+40 nmol·mol-1 of O3), two watering regimes (well-watered and reduced watering at 40% of well-watered irrigation), and two soil nitrogen addition treatments[no addition and the addition of 50 kg·(hm2·a)-1]. The results showed that O3 stress significantly increased the content of soluble sugar in leaves and starch in fine roots but decreased the content of starch and total non-structural carbohydrate (NSC) in leaves. Drought stress significantly reduced the content of starch and total NSC in leaves but increased the contents of soluble sugar and total NSC in fine roots. Nitrogen addition had no significant effect on NSC and its components in leaves and fine roots. NSC and its components in leaves and fine roots were positively correlated with photosynthetic rate and biomass. With an increase in the number of environmental stress factors, NSC in leaves showed a significant downward trend while NSC in fine roots showed a significant upward trend. The study demonstrates that environmental stress can promote the transformation of starch into soluble sugars in plant leaves and the transfer of NSC from leaves to roots for storage, which may be a coping strategy for plants exposed to environmental stress.

[Progress in the Interactions of Ozone Pollution and Other Environmental Stress on Urban Forests in China].

Ground-level ozone pollution(O3) and climate change have become key global problems threatening the environment and sustainable development of urban forests. At present, various studies have assessed the O3 impacts on trees; however, it is difficult to accurately evaluate the complex ecological effects caused by multiple factors on the natural urban environment. In this paper, the interactions between O3 and carbon dioxide(CO2), drought, nitrogen deposition, and warming, as well as the effects of the physiology, biochemistry, and growth of urban trees in China were reviewed. Elevated CO2 could alleviate the negative effects of elevated O3 on the photosynthetic metabolism, antioxidant system, and growth of trees. There is a complex interaction between O3 and drought, which may synergistically aggravate, alleviate, or have no effect on trees. However, there was no correlation between O3 and N deposition, only a significant interaction between elevated temperatures and O3, which slowed down the adverse effects of O3 on tree growth and photosynthesis. Finally, suggestions are put forward to manage and sustainable develop urban forests in China under future climate change and air pollution.

[Preliminary Screening for the Urban Forest Against Combined Air Pollution].

Combined air pollution has become one of the most important city diseases in China. The construction of an urban forest not only needs landscape aesthetics, but also requires selecting a plant of high comprehensive tolerance threshold based on the needs of the ecological environment of each city, which has become a standard to maintain the sustainable development of the urban forest ecological function under environmental pollution. According to the comprehensive factor analysis of the sorption and absorption capacity of 537 plants to six air pollutants (i.e., sulfur dioxide, nitrogen dioxide, hydrogen fluoride, chlorine, ozone, and particulate matters), the results showed that the tree species with strong comprehensive tolerance ability to six air pollutants were Morus alba, Platycladus orientalis, and Ailanthus altissima; the tree species with medium comprehensive tolerance ability were Populus tomentosa, Acer truncatum, Sabina chinensis, Amygdalus davidiana, Salix babylonica, Paulownia fortunei, and Pinus tabulaeformis; the trees species with relatively weak comprehensive tolerance ability were Robinia pseudoacacia, Populus×canadensis, Ginkgo biloba, Juglans regia, Platanus acerifolia, Koelreuteria paniculata, Lagerstroemia indica, and Forsythia suspensa. According to the characteristics of climate, economic structure, and air pollutants of the cities in the north and south of China, the urban forest should be constructed using selected species with a strong comprehensive tolerance ability to achieve maximum purification effect of the urban forest ecological service function.

[Emission Characteristics of Biogenic Volatile Compounds (BVOCs) from Common Greening Tree Species in Northern China and Their Correlations with Photosynthetic Parameters].

In order to understand the emission characteristics of common greening trees in Beijing and analyze their correlations with photosynthetic parameters, including the net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (ci), and transpiration rate (Tr), we collected samples of biogenic volatile organic compounds (BVOCs) using a dynamic sampling technique from 14 species of deciduous trees. The results showed that there were significant differences in isoprene and total BVOC emissions between family or genus levels (P<0.01). With the exception of Lonicera maackii Maxim and Ulmus pumila L., all species were found to emit isoprene, monoterpenes, and sesquiterpenes, of which, species from the Salicaceae (e.g., Populus deltoides cv. '55/56'× P.deltoides cv. 'Imperial', P. euramericana cv. '74/76', Populus simonii Carr, and Salix babylonica) and Legume (Sophora japonica, Robinia pseudoacacia, and S. japonica Linn. var. japonica f. pendula Hort) families were the higher isoprene emitters, with emission rates that ranged from (30.1±4.3) µg·(g·h)-1 to (91.8±10.0) µg·(g·h)-1. Plants from the Oleaceae (e.g., Fraxinus chinensis Roxb and Syringa oblata Lindl), Begonia (Malus prunifolia), Sapindaceae (Koelrenteria paniculate), and Aceraceae (Acer truncatum Bunge) families mainly emitted monoterpenes and sesquiterpenes. Among them, Fraxinus chinensis Roxb and Acer truncatum Bunge were the highest emitters with emission rates of (10.6±4.8) µg·(g·h)-1 and (11.8±6.4) µg·(g·h)-1, respectively. Ocimene and ß-pinene were the two main monoterpenes emitted from greening tree species. No significant correlations were found between the emission of BVOCs and Pn or gs, while the emission rate of isoprene (r=0.681; P<0.01) and the total BVOC (r=0.698; P<0.01) from the Salicaceae family increased with increasing Tr. Moreover, leguminous plants showed a significant positive correlation between the total BVOC emission rate and ci (P=0.04). This study provides a scientific reference for the selection and configuration of urban greenery, and a theoretical basis for exploring the mechanism of BVOC emissions.

[Inventory and Characteristics of Biogenic Volatile Organic Compounds (BVOCs) for 12 Deciduous Fruit Trees].

To better understand the emission of biogenic volatile organic compounds (BVOCs) in suburbs, we selected 12 typical deciduous fruit trees and conducted field sampling and laboratory analysis of BVOCs using a dynamic sampling technique. To our knowledge, details of BVOC emissions for nine of the selected fruit tree species are reported here for the first time. Emissions of BVOCs from fruit trees contained nine kinds of compounds, including hydrocarbons, alcohols, and aldehydes, of which hydrocarbons accounted for up to 39.0%. All fruit trees were found to emit isoprene and monoterpenes (six species also emitted sesquiterpenes), of which three species were high emitters and nine species, such as Catalpa, were medium emitters. The emission rates of total BVOCs (including isoprene, monoterpenes, and sesquiterpenes) from different fruit trees ranged from (2.6±0.1) µg·(g·h)-1 to (14±0.8) µg·(g·h)-1. Analyses of BVOCs from different families and plant forms indicated that isoprene emission rates were significantly higher from woody fruit trees[(4.2±1.4) µg·(g·h)-1] than from vine fruit trees[(0.6±0.2) µg·(g·h)-1, P=0.03], whereas there was no significant difference between family or genus. This suggests that the emission level of BVOCs from fruit trees cannot be classified by family and genera. In contrast to coniferous plants, ß-myrcene, D-limonene, and γ-terpinene-associated with floral or resinous aromas-were the main monoterpenes of fruit trees. The emission rate of ß-myrcene was highest, accounting for 59.3% of the total monoterpene emissions. In addition, fruit trees may emit eight other fragrant VOCs listed as hazardous air pollutants (HAPs), e.g., fluorene, phenanthrene, and naphthalene. This study expands the field of BVOCs research and provides basic data for enriching the BVOCs database, as well as for evaluating the environmental effects of BVOCs.

[Spatial and Temporal Variations in Fertilizer Use Across Prefecture-level Cities in China from 2000 to 2015].

Chemical fertilizer plays an important role in increasing grain production in agricultural systems but overuse also brings a series of environmental problems, such as eutrophication of surface water, deterioration of soil structure, and the decline of agricultural carrying capacity. At present, research on chemical fertilizer use mainly focuses on utilization efficiency while studies on the spatial characteristics of its use are limited. It is also of great significance for the sustainable development of agriculture in China to fully understand the spatial changes in the use of chemical fertilizers. Based on data of pure chemical fertilizer use, sown area, and grain yield in prefecture-level cities from 2000 to 2015, spatial autocorrelation analysis, cold and hot spot analysis, nuclear density analysis, and standard deviation ellipse analysis were applied. The temporal and spatial variations in total fertilizer use and fertilizer load per unit area in 2000, 2005, 2010, and 2015 were compared. The results showed that:① The use of chemical fertilizer in China increased linearly from 2000 to 2015 but it has been in a relatively high agglomeration state in the region. The pure use of chemical fertilizer experienced a process of increasing regional aggregation from 2000 to 2005, weakening from 2005 to 2010, and increasing from 2010 to 2015. ② From a spatial perspective, the total amount of chemical fertilizer applied between 2000 and 2015 showed an increasing trend, shown by an increase in the number of prefecture-level cities and regions in which the use of chemical fertilizer exceeded the standard. The eastern regions of China, which have experienced rapid economic development, such as Guangdong Province and Fujian Province, are over the critical load of chemical fertilizer more and denser than other prefecture-level cities because the proportional reduction in sown area is greater than the increase in chemical fertilizer use. ③ The movement track of the grain production center in China from 2000 to 2015 was not consistent with the movement track of chemical fertilizer usage. Specifically, the center of grain production moves to the northeast, while the center of chemical fertilizer use moves to the west. This demonstrates that the status of commercial grain production in Northeast China is becoming more and more important, and that the use of chemical fertilizer in the western regions of China is gradually increasing. Here, there is a trend for exceeding the standard, which required further attention.

[Effects of Elevated Ozone on Biogenic Volatile Organic Compounds (BVOCs) Emission: A Review].

With the global increase of tropospheric ozone (O3) and complex interactions between biogenic volatile organic compounds (BVOCs) emissions and tropospheric O3 concentrations, this review summarizes current research progress and future research prospects in terms of the effects of elevated O3 on BVOCs emissions. The main progress included impacts of BVOCs categories, plant functional types, O3 sensitivity of plants, the O3 stress level on the response of BVOCs emissions to single O3 stress, and the combined effects of elevated O3 and temperature, carbon dioxide (CO2), drought, and nitrogen (N) deposition. Results indicated that most published results reported no change in BVOCs emissions in response to increasing O3 concentration. Specifically, decreasing effects of O3 on BVOCs emissions were more obvious in studies on isoprene and deciduous species, whereas studies on monoterpenes and evergreen plant species showed more results with an increasing trend as well as acute O3 exposure experiments. There was an increased tendency of monoterpene emissions to the combined effects of O3 and temperature or N deposition. However, the combined effects of O3 and CO2 decreased isoprene emissions. Given that studies on the effects of O3 on BVOCs emissions remain scarce, more complete experiments are needed that consider differences between short-term and long-term or individual-level and ecosystem-level. Furthermore, future research should strengthen the multi-factor interactive studies, particularly on O3 and other global change components and biotic and abiotic stresses, to assess BVOCs emissions from terrestrial ecosystems in response to O3 pollution both currently and in the future, which will provide valuable theoretical support to air pollution control.

[Interactive Effects of Ozone and Drought on Antioxidant Enzyme Activities of Poplar Leaves].

Ground-level ozone (O3) pollution and drought have become major environmental factors that threaten the normal growth of plants. In this study, we determined the effects of three O3 concentrations (charcoal-filtered air, CF, non-filtered air, NF and non-filtered air+40 nmol·mol-1, NF40), two water treatments (well-watered, WW, and mild drought, MD, 60% of WW in volumetric soil water content), and their interactions on the light-saturated photosynthesis rate (Asat) and on the activity of antioxidant enzymes and soluble proteins of the poplar '546' (Populus deltoids cv. 55/56×P. deltoides cv. Imperial). Results showed that Asat significantly decreased with elevated O3, and with interactions between O3 and drought. Drought significantly reduced the activities of catalase (CAT) and superoxide dismutase (SOD) but did not affect the activities of peroxidase (POD) or ascorbate peroxidase (APX). Reduction ranges in CAT and SOD increased with drought duration. APX activity significantly decreased with increasing O3 and drought, but soluble protein content did not. Activities of antioxidant enzymes were not significantly affected by elevated O3 and their interactions. Results provide a scientific basis for protection of poplar plantations in response to increasing O3 concentrations and drought under environmental changes.

Antifungal and eliciting properties of chitosan against Ceratocystis fimbriata in sweet potato.

The inhibitive effects of chitosan on black rot disease caused by Ceratocystis fimbriata in sweet potato tuber root (TR) were evaluated. The results demonstrated that chitosan effectively inhibited the mycelial growth and spore germination of C. fimbriata and directly led to the cell necrosis. Chitosan altered the chitin deposition and influenced the fatty acid composition of C. fimbriata. The application of chitosan effectively controlled the C. fimbriata development in sweet potato TRs 17 days of storage 25 °C. Phenylalanine ammonia lyase (PAL) and superoxide dismutase (SOD) activity were clearly enhanced by the chitosan treatment, while the malondialdehyde (MDA) production was not increased. These findings suggest that chitosan effectively controlled the infection of C. fimbriata in sweet potato TRs owing to its antifungal and eliciting properties, which induced some defense responses during storage.

[Dry and Bulk Nitrogen Deposition in Suburbs of Xining City].

This study conducted a full two-year (2014 and 2015) measurements of dry and bulk deposition of atmospheric inorganic nitrogen (N) at the suburb of Xining city, Qinghai province. Dry N deposition fluxes were calculated by multiplying the atmospheric concentrations of NH3 and NO2 measured using passive samplers with the modeled dry deposition velocities provided by the GEOS-Chem global chemical transport model, while bulk N deposition fluxes were measured using precipitation gauge. Annual mean concentrations of gaseous NH3 and NO2 averaged 8.8 and 19.6 µg·m-3, respectively, with significantly higher values in 2015 than in 2014. Seasonal mean NH3 concentrations were higher in spring and summer than in autumn and winter, but the concentrations of NO2 changed little from season to season, with a small peak in autumn. Annual mean concentrations of NH4+-N and NO3--N in precipitation averaged 2.2 and 1.8 mg·L-1, respectively. Concentrations of NH4+-N in autumn were~55% lower than those in other seasons, whereas those of NO3--N in autumn or winter were~26% higher than those in spring and summer. Dry deposition of NH3 and NO2 was 9.0 and 2.8 kg·(hm2·a)-1, respectively. Bulk deposition of NH4+-N and NO3--N in precipitation was 7.6 and 6.2 kg·(hm2·a)-1, respectively. Reduced N (gaseous NH3 and NH4+-N in precipitation) was the dominant form of N deposition. The total dry and wet N deposition was 25.6 kg·(hm2·a)-1, which represented significant nutrient input from the environment to the suburban farmland, but this amount of deposited N exceeded the critical loads[10-20 kg·(hm2·a)-1] of terrestrial ecosystems, suggesting a risk of "N saturation" in the local natural environment.

[Photosynthetic Characteristics and Ozone Dose-response Relationships for Different Genotypes of Poplar].

The open top chambers were used to explore the photosynthetic characteristics of three genotypes of poplar ('546', '90' and '84K') in response to different ozone exposures. The results showed that net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE), apparent electron transport rate (ETR), excitation energy capture efficiency of PSⅡ reaction center (F'v/F'm), coefficient of photochemical quenching (qP), actual photochemical efficiency of PSⅡ in the light (PhiPS2), chlorophyll a (Chla), chlorophyll b (Chlb), total chlorophyll (Chla+b) and carotenoid (Car)contents were significantly decreased with the increasing ozone concentrations. However, intercellular CO2 concentration (ci) was significantly increased and stomatal conductance (Gs) remained unchanged. There was significant difference in photosynthetic characteristics among three genotypes of poplar. The genotype'546' showed a significant linear correlation (P<0.01) between photosynthetic parameters (except Gs) and the ozone dose index AOT40(accumulated hourly O3 concentration over a threshold of 40 nmol·mol-1 during daylight hours). Among the three genotypes of poplar, photosynthesis pigments contents in '546' significantly declined with the increase of ozone concentration but not in '90' and '84K'. According to the linear relationship of most photosynthetic parameters and AOT40, especially the total chlorophyll, '546' showed the maximum slope, follows by '90' and then '84K'. So the order of the ozone sensitivity of three poplar genotypes was '546'> '90'> '84K'. The results of this study can provide an important basis for breeding ozone resistant genotype of poplar as well as protecting poplar from ozone damage.

[Effects of Elevated Ozone and Nitrogen Deposition on Photosynthetic Characteristics and biomass of Populus cathayana].

The open top chambers were used to explore the influences of nitrogen deposition on the response of photosynthetic characteristics of Populus cathayana to ozone. The results showed that the net photosynthetic rate (Pn), apparent electron transport rate (ETR), excitation energy capture efficiency of PSⅡ reaction center (F'v/F'm), coefficient of photochemical quenching (qP), the maximum of carboxylation efficiency (Vcmax) and the maximum rate of electron transport (Jmax) were significantly decreased with the increasing O3 concentration. However, intercellular CO2 concentration (ci) was significantly increased and stomatal conductance (Gs) remained unchanged. There was significant difference in biomass at the end of growing season. However, in a certain extent, nitrogen deposition improved photosynthetic capacity and biomass of P. cathayana. The interaction of O3 and nitrogen deposition was not significant in terms of plant photosynthetic characteristics. The current results provided scientific basis for the protection of P. cathayana in response to the global O3 concentration and nitrogen deposition increase.