Bacterial colonization of the phyllosphere of nineteen plant species and antimicrobial activity of their leaf secondary metabolites against leaf associated bacteria

Summary. The scope of this work was to examine whether leaf constitutive secondary metabolites play a role in determining bacterial colonization of the phyllosphere. To this aim, we surveyed nineteen native or cultivated plant species that share a common bacterial pool in a North Mediterranean area, and estimated the size of total and ice nucleation active (INA) bacterial populations on their leaves. Large differences in the colonization of their phyllosphere were found; the population size of epiphytic bacteria ranged from 7.5 × 10² to 1 × 10⁶ CFU/g fresh weight, in eucalypt and celery, respectively. Species native in Mediterranean-type climate areas, particularly those belonging to the group of aromatic plants, are characterized by scarce presence of INA bacteria. The antibacterial activity of essential oils, surface phenolics and leaf tissue extracts was also estimated against the INA strains P. syringae and E. herbicola, isolated from two of these plant species. E. herbicola proved more sensitive than P. syringae. Of the species examined, oregano [Origanum vulgare L. subsp. hirtum (Link.) Ietswaart], an aromatic plant, had the highest antimicrobial activity, whereas six species showed no activity at all. Further experiments were performed with oregano and bean (Phaseolus vulgaris L.) that represent two extremes in their secondary metabolite content. Both plants were inoculated with P. syringae. By the end of incubation, the bacterial population on bean plants was about 100 times higher than that on oregano leaves. Scanning electron micrographs showed that bacterial growth on oregano leaves was confined to sites away from glandular hairs. Results from the bacterial colonization survey together with those from the toxicity tests showed that all species rich in antibacterial secondary metabolites harbored low leaf bacterial populations. These results provide substantial evidence that leaf secondary metabolites function as constitutive defense chemicals against microbial invasions. However, the fact that species with non- or moderately active leaf secondary metabolites are not always highly colonized suggests mediation of other unknown factors, the contribution of which requires further investigation.     

Characteristics and recent trends of sulfur dioxide at urban, rural, and background sites in North China: Effectiveness of control measures

SO₂ measurements made in recent years at sites in Beijing and its surrounding areas are performed to study the variations and trends of surface SO₂ at different types of sites in Northern China. The overall average concentrations of SO₂ are (16.8 ± 13.1) ppb, (14.8 ± 9.4) ppb, and (7.5 ± 4.0) ppb at China Meteorological Administration (CMA, Beijing urban area), Gucheng (GCH, relatively polluted rural area, 110 km to the southwest of Beijing urban area), and Shangdianzi (SDZ, clean background area, 100 km to the northeast of Beijing urban area), respectively. The SO₂ levels in winter (heating season) are 4-6 folds higher than those in summer. There are highly significant correlations among the daily means of SO₂ at different sites, indicating regional characteristics of SO₂ pollution. Diurnal patterns of surface SO₂ at all sites have a common feature with a daytime peak, which is probably caused by the downward mixing and/or the advection transport of SO₂-richer air over the North China Plain. The concentrations of SO₂ at CMA and GCH show highly significant downward trends (-4.4 ppb/yr for CMA and -2.4 ppb/yr for GCH), while a less significant trend (-0.3 ppb/yr) is identified in the data from SDZ, reflecting the character of SDZ as a regional atmospheric background site in North China. The SO₂ concentrations of all three sites show a significant decrease from period before to after the control measures for the 2008 Olympic Games, suggesting that the SO₂ pollution control has long-term effectiveness and benefits. In the post-Olympics period, the mean concentrations of SO₂ at CMA, GCH, and SDZ are (14.3 ± 11.0) ppb, (12.1 ± 7.7) ppb, and (7.5 ± 4.0) ppb, respectively, with reductions of 26%, 36%, and 13%, respectively, compared to the levels before. Detailed analysis shows that the differences of temperature, relative humidity, wind speed, and wind direction were not the dominant factors for the significant differences of SO₂ between the pre-Olympics and post-Olympics periods. By extracting the data being more representative of local or regional characteristics, a reduction of up to 40% for SO₂ in polluted areas and a reduction of 20% for regional SO₂ are obtained for the effect of control measures implemented for the Olympic Games.     

北运河流域(北京段)沉积物中PAHs污染特征与风险评估

为探明北运河流域（北京段）多层沉积物中PAHs（多环芳烃）的污染状况,利用活塞式底泥取样器于2014年11月采集了9处沉积物样品,取样深度为30~80 cm,每处样品根据其垂向介质特征大致分成3~4层,分别测定各层样品的粒径、TOM（总有机质）及16种PAHs的质量分数,探讨PAHs在河道沿程与垂向上的分布特征、来源及生态风险评价.结果表明,北运河流域（北京段）沉积物以砂质壤土为主,w（TOM）（以干质量计,下同）为103.4~146.8 g/kg,w（∑₁₆PAHs）为598.1~28 730.6 ng/g,各层w（∑₁₆PAHs）为108.5~8 810.8 ng/g.沉积物中PAHs以高环为主,主要包括有Phe（Phenanthrene,菲）、Fla（Fluoranthene,荧蒽）、Pyr（Pyrene,芘）、BbF〔Benzo（b）fluoranthene,苯并[b]荧蒽〕.在河道沿程变化上,中下游沉积物的污染程度远高于上游.在垂向变化上,w（TOM）和沉积物粒径对PAHs的分布影响有限,PAHs的垂向分布主要受所处沉积环境与历史污染程度影响.根据主成分分析与同分异构体比值法推断,PAHs主要来源于化石燃料与生物燃料的燃烧,少部分为石油源.利用效应区间值得出的生态风险评价结果表明,北运河流域（北京段）沉积物中PAHs可能已对环境产生负面影响,其中BbF、BkF、InP与BgP已对环境产生毒副作用,需要给予关注与解决.      

瀑河水库蓄水后水质变化预测

瀑河水库拟作为南水北调中线的一个调蓄水库。在瀑河水库淹没区内布10个采样点，分别采集0－20、20－40、40－60cm深度的土壤，实验室中模拟水库蓄水淹没情景，连续监测“库水”水质，试验表明：蓄水初期土壤中营养物质溶出对库水水质有一定影响，且随着时间的推移，各营养物质溶出的速度及浓度变化不同，蓄水16天后浓度趋于平稳，库水水质达到地表水环境质量Ⅱ类标准，将模拟值作为初始值，利用WQRRS模型进行运行期水质预测，得到结论为：（1）当调水水质为Ⅰ和Ⅱ类标准值的中值、流域汛期径流水质为Ⅱ－Ⅴ类时，预测库水水质为Ⅱ－Ⅲ类；（2）当调水水质为Ⅱ类标准值的下限值、流域汛期径流水质为Ⅱ－Ⅴ类时，预测库水水质大多为Ⅲ类，部分情况下为Ⅳ类，且N、P超标；（3）当调水水质为Ⅰ和Ⅱ类标准值的中值、流域径流水质为Ⅱ类时，在2010、2020和2030水平年水库水质全部为Ⅱ类；当调水水质为Ⅱ类标准值的下限值时库水水质则为Ⅲ类。     

贵州省西部环境灾害与防治

本文分析了贵州西部环境灾害的形成原因，它既受自然因素的影响，也受人类活动的影响。并提出了防治贵州西部环境灾害的基本措施。     

Mercury accumulation in soils and plants in the Almadén mining district, Spain: one of the most contaminated sites on Earth

Although mercury (Hg) mining in the Almadén district ceased in May 2002, the consequences of 2000 years of mining in the district has resulted in the dissemination of Hg into the surrounding environment where it poses an evident risk to biota and human health. This risk needs to be properly evaluated. The uptake of Hg has been found to be plant-specific. To establish the different manners in which plants absorb Hg, we carried out a survey of Hg levels in the soils and plants in the most representative habitats of this Mediterranean area and found that the Hg concentrations varied greatly and were dependent on the sample being tested (0.13–2,695 μg g⁻¹ Hg). For example, the root samples had concentrations ranging from 0.06 (Oenanthe crocata, Rumex induratus) to 1095 (Polypogon monspeliensis) μg g⁻¹ Hg, while in the leaf samples, the range was from 0.16 (Cyperus longus) to 1278 (Polypogon monspeliensis) μg g⁻¹ Hg. There are four well-differentiated patterns of Hg uptake: (1) the rate of uptake is constant, independent of Hg concentration in the soil (e.g., Pistacia lentiscus, Quercus rotundifolia); (2) after an initial linear relationship between uptake and soil concentration, no further increase in Hg_plant is observed (e.g., Asparagus acutifolius, Cistus ladanifer); (3) no increase in uptake is recorded until a threshold is surpassed, and thereafter a linear relationship between Hg_plant and Hg_soil is established (e.g., Rumex bucephalophorus, Cistus crispus); (4) there is no relationship between Hg_plant and Hg_soil (e.g., Oenanthe crocata and Cistus monspeliensis). Overall, the Hg concentrations found in plants from the Almadén district clearly reflect the importance of contamination processes throughout the study region.     

The Botanist Effect Revisited: Plant Species Richness, County Area, and Human Population Size in the United States

Abstract:  The "botanist effect" is thought to be the reason for higher plant species richness in areas where botanists are disproportionately present as an artefactual consequence of a more thorough sampling. We examined whether this was the case for U.S. counties. We collated the number of species of vascular plants, human population size, and the area of U.S. counties. Controlling for spatial autocorrelation and county area, plant species richness increased with human population size and density in counties with and without universities and/or botanical gardens, with no significant differences in the relation between the two subsets. This is consistent with previous findings and further evidence of a broad-scale positive correlation between species richness and human population presence, which has important consequences for the experience of nature by inhabitants of densely populated regions. Combined with the many reports of a negative correlation between the two variables at a local scale, the positive relation between plant species richness in U.S. counties and human population presence stresses the need for the conservation of seminatural areas in urbanized ecosystems and for the containment of urban and suburban sprawl.     

Factors driving the seasonal dynamics of Pseudo-nitzschia species and domoic acid at mussel farming in the SW Mediterranean Sea

ABSTRACT

The seasonal variations in Pseudo-nitzschia species and domoic acid (DA) concentration were investigated, at three shellfish farms in SW coastal Mediterranean. In parallel, the toxicity of mussels was tested. Two distinct groups of species were enumerated according to morphology and size (Pseudo-nizschia delicatissima and P. seriata groups). DA was detected over a nine-week period from July to October 2012 in the Lagoon, with a maximum concentration recorded in July (12.71?ng?DA?L^?1). DA was positively correlated with the presence of P. seriata-group and P. delicatissima-group and was mostly occurred during P limitation period in seawater. No DA was found in mussels that were collected during the period of DA absence in seawater. Our results suggest that temperature, salinity, inorganic and organic nutrients were significant for the seasonal dynamics of P. seriata and P. delicatissima groups, but that the P limitation was the most driving factor for DA production in these areas. The relative influence of environmental factors should be further studied to better understand the recent surfacing of massive blooms of toxigenic Pseudo-nitzschia in SW Mediterranean coast.     

亚高山30a人工针叶林物种多样性的定量分析

探讨了川西地区不同海拔梯度上,30a亚高山人工针叶林乔,灌,草各层物种多样性的变化规律,并运用逐步多元回归分析方法,分析了不同立地条件下土壤因子与针叶林群落乔,灌,草各层物种多样性指数之间的关系,结果显示：30a人工针叶林灌木层和草本层多样性指数明显高于乔木层;随着海拔的升高,灌木层和草木层物种的多样性指数逐渐降低,在halt2700m处多样性最丰富,乔木物种多样性则呈现为“低→高→低”的变化趋势,符合“中间高度膨胀（mid-altitude bulge)模式,土壤因子对30a人工恢复针叶林多样性的影响主要是体现在灌木层和草本层的变化,而对乔木层物种多样性的影响不明显,土层厚度,土壤容重,石砾含量,枯枝落叶的贮量,CaO含量以及有机质的C／N比值等土壤因子与灌木层和草本层物种多样性之间存在线性相关关系,分层建立了物种数,Simpson指数,ShannonWiener指数,Menhinick指数以及Brillouin指数与相关土壤因子的回归模型。     

Potential allelopathic effect of Pinus halepensis in the secondary succession: an experimental approach

Summary. Recent economic and social changes in north Mediterranean regions have led to an important rural depopulation. Consequently, meadows developed on abandoned agricultural lands (characterized by high species richness) undergo reforestation. These former fields are mainly colonized by Pinus halepensis Miller, which is known to synthetize a wide range of secondary metabolites, among these, some could influence plant succession through allelopathy. The allelopathic potential of P. halepensis, was tested against two target species (Lactuca sativa L. and Linum strictum L.) with aqueous extracts obtained from different organs (root and needle) taking into account the individual age (±10, ±30 and > 60 years old). Root and needle extracts affected differently germination and growth of the two target species, the responses varying with concentration of extracts, age and organs tested. The strongest inhibitory effect was observed on the germination and growth of L. strictum, exposed to needle extracts of young P. halepensis (±10 years old), and root extracts of older P. halepensis (> 30 years old). These extracts contained several phenolic acids (e.g. 4-hydroxybenzoic acid and p-coumaric acid), which are known as allelochemicals and their concentrations vary with age and organ tested. Hence, P. halepensis could influence secondary succession through the release of potential allelochemicals in the environment by leaf leachates or root exudates.