Responses of microbial populations in the rhizosphere to deposition of simulated acidic rain onto foliage and/or soil

Air pollutants or some chemicals applied to plant foliage can alter the ecology of the rhizosphere. Experiments were conducted to distinguish among possible foliage-mediated versus soil- or root-mediated effects of acid deposition on microorganism in the rhizosphere. Seedlings of a sorghum x sudangrass hybrid in pots of non-sterile soil-sand mix in a greenhouse were exposed to simulated rain solution adjusted with H2SO4 + HNO3 to pH 4.9, 4.2, 3.5 or 2.8. Solutions were applied as simulated rain to foliage and soil, foliage only (soil covered by plastic, and deionized water applied directly to the soil), or soil only (solution applied directly to the soil). Solutions were applied on 16 days during a 6-week period (1.5 cm deposition in 1 h per application). Plant shoot and root dry weights and population densities of selected types of bacteria, filamentous actinomycetes and fungi in the rhizosphere were quantified after exposures were completed. Deposition of simulated acidic rain onto foliage alone had no effect on plant biomass or microbial population densities in the rhizosphere (colony-forming units per gram of rhizosphere soil). However, plant growth was stimulated and all microbial populations in the rhizosphere increased 3- to 8-fold with increased solution acidity (relative to pH 4.9 solution) when solution penetrated the soil. Statistical analyses indicated that the acid dose-population response relationships for soil-only and foliage-and-soil applications were not different. Thus, no foliage-mediated effect of simulated acidic rain on rhizosphere ecology was detected.     

Relation between mortality of young walleye (Stizostedion vitreum) and recruitment with different forms of compensation

The relation between mortality of young fish and recruitment is important for assessment of the environmental effects of facilities that kill large numbers of young fish, such as electric power stations and hydropower plants. A simulation model with a bioenergetic growth component was applied to examine the relation between mortality of young and recruitment for walleye (Stizostedion vitreum) with different forms of population regulation, including: food limited growth, food limited growth with size-dependent mortality, and food limited growth with age at maturity dependent on size. With food limited growth small increases in mortality of young reduced recruitment considerably, but the population slowly approached a new equilibrium. If mortality of young increased when growth was food limited, the population approached a new equilibrium of natality and mortality because with fewer individuals there was more food per individual, and individuals were larger in size and produced more eggs; this feedback adjusted natality to equal mortality. With either mortality or age at maturity dependent on size, large increases in mortality of young resulted in only small decreases in recruitment.     

Training refugees as primary health care workers: Past imperfect, future conditional

Many problems have been encountered in the planning and implementation of health care in refugee camps, and more specifically in the training of refugees as primary health care workers. A review of the published literature and a "survey" of the opinions and experiences of refugee, national and international health personnel regarding training has therefore been undertaken to provide an overview of what has been done and to make recommendations for future work.
The review highlights the need to reallocate resources away from high visibility emergency aid to development activities, such as training, that will create an infrastructure for primary health care and promote self-reliance.     

Identifying the land use and land cover change drivers: methods and case studies of two forest reserves in Northern Benin

Environment, Development and Sustainability - Land use and land cover change (LULCC) is one of the problems that the world has been facing for the last few decades despite political attention....     

pH值对亚硝酸盐氧化菌动力学及功能基因的影响

为探究pH值对亚硝酸盐氧化菌（NOB）活性动力学影响,本试验采用序批式活性污泥（SBR）反应器,以富含NOB的活性污泥为对象,基于Monod模型考察不同pH值对NOB活性动力学的影响并进行统计学分析.结果表明,Monod方程可较好地反映不同pH值条件下基质底物浓度对NOB比亚硝态氮氧化速率（SNiOR）的影响,且pH=7.0时动力学参数Ks为（6.167mg/L）,r_max为[1.134g/（g·d）],此时NOB活性最好.利用钟形经验模型进行非线性回归拟合,最大比降解速率（r_max）随pH值的增大呈钟形变化,本试验NOB的最佳pH值为（6.9±0.1）,其中r_max维持在r_opt一半以上的pH值范围（ω）为（3.26±0.4）.以亚硝酸盐氧化还原酶类基因（nxrA、nxrB）为引物,基于荧光定量PCR技术分析结果显示,在不同pH值条件下nxrA基因和nxrB基因拷贝数的变化趋势均与动力学参数（Ks、r_max）的规律一致,且nxrA和nxrB基因在系统的降解过程中起协同作用.